Concrete Skatepark Construction
This section provides a step-by-step guide to the specialized technology you need to know for successful skatepark construction. The goal is to impart to a contractor or serious do-it-yourselfer the general principles of forming, jigging and construction of a modern skatepark. This basic knowledge of the technology can then be adapted and applied to any skatepark design.
The methodology shown is by no means the fastest, most efficient or "tech" form of skatepark construction. It is however a simple, easy to understand method that has the benefit of being highly stable. This allows for longer construction times without site degradation. Enjoy!
The information offered is taken directly from "The Complete Step by Step Guide to Concrete Skatepark Construction". The complete guide is available for 24.95 shipped anywhere in the world and can be ordered by following the link on any page.
Construction Methods Contents
Before construction, the site must be cleared of all organic matter including trees and brush. If trees must be cut down be sure that the entire root-ball is removed as any organic material will eventually decompose, leaving a void which can cause cracking or breakage. After the area is clear of organic debris, crushed gravel should be spread covering the entire site.
It is not wise to pour concrete directly over earth even if it is compacted because of the tendency of the earth under the concrete to settle. Settling earth will result in cracking concrete. A poorly compacted base most often causes cracking and settling of concrete. A proper sub-base of compacted gravel is essential for proper skatepark construction in all but the mildest climates. It is recommended that skatepark construction begin with a minimum of 4 inches of “¾ inch minus” (3/4 inch or smaller) crushed gravel, which is then wet and compacted. A compactor or “whacker” can be rented by the day or week from most equipment rental companies. This insures a suitable base and will reduce the likelihood of cracking in the future. The site can now be staked out, and the space for bowls and/or obstacles identified with paint or stakes and string line.
Concrete provides an attractive, smooth and easily maintained surface for skatepark construction. This makes concrete parks safer than other construction options.
Building a skatepark is a sizable job, so it should be split into a series of smaller jobs. This will control the amount of concrete to be placed at one time. The formula for estimating concrete volume is provided in Basic Concepts section. For skatepark construction use 4000 psi (pounds per square inch) concrete to a minimum depth of 4 inches. This is poured over a minimum depth of 4 inches of “¾ minus” (3/4 inch in diameter or less) compacted gravel (as described above). Never use “fire water” or other concrete curing accelerators unless you are highly experienced in skatepark construction. Using a curing accelerator makes it likely that the concrete will set-up before proper hard trowel finishing can be completed.
Structural support of the concrete comes from using number three (3/8 inch) rebar, placed and tied on a minimum of 12-inch centers. For a skatepark this is strong stuff and will result in a slab stronger than most people’s driveways. Obviously, through normal use there will never be anywhere near that type of stress on the slab of the skatepark. However, this superior material will keep future cracking to a minimum.
For large construction projects like a skatepark the concrete is best placed with a pump truck. A concrete pump truck is a specialized piece of machinery that can pump concrete through a tube attached to an overhead boom over a distance of 150 feet or more. The last 10 feet of the tube is flexible and has handles, so that it can be moved several feet in any direction while the concrete is being pumped. The individual placing the concrete manually controls the flexible end of the tube. The person placing concrete must remain alert and aware of the presence of fellow workers. The pressure necessary to pump concrete through the tube is substantial. If there is any air in the line, the flexible end of the tube can get tossed around like a fire hose, with risk of physical injury to anyone near-by. The pump truck operator controls the boom and the flow of concrete being placed. The pump truck operator and the person placing the concrete communicate through a series of hand signals. Talk with the driver well in advance so that you know what these signals are.
If and when you go to a structural engineer for advice or review of the design specifications for your skatepark, he or she will probably recommend that expansion joints be placed in the concrete at least every 8 feet (like a driveway) and offer you other recommendations that are perfectly appropriate for general concrete construction. However, these recommendations are not appropriate for skateparks. You will have to become an advocate for the uncommon methods used in modern skatepark construction as outlined in this book. Take this information with you to such meetings. The most important thing to help structural engineers and others understand about these techniques is to help them realize you are not building a parking lot or a sidewalk. You are building a large concrete form specifically designed and engineered for the sport of skateboarding. Form follows function. The continuous concrete construction of a skatepark as described here results in random hairline cracking which is not felt through the wheels of a skateboard and will, therefore, not disrupt the ride (see following sections). This construction approach is better for the building of concrete skateparks than the methods most engineers are familiar with. Typical engineering methods result in controlled cracking through a series of expansion joints which results in the all too familiar ka-chunk, ka-chunk, ka-chunk of a standard sidewalk. Memorize and keep repeating the following statement; “we understand that we are making a trade-off, but random hair-line cracking is better than expansion joints and will be kept to a minimum because we are using 4000 psi concrete (as strong as it gets) over compacted fill (3/4 minus) with number three (3/8 inch rebar) as reinforcement.”
1 inch maximum aggregate.
Minimum 520 pounds cement per cubic yard.
Maximum 2-inch slump.
6 % plus/minus 1½% air.
NO fire water or other curing accelerators.
Have you ever watched someone ride a skateboard down a sidewalk and heard that ka-chunk, ka-chunk, ka-chunk sound as the wheels make contact with the expansion joints in the concrete? We are going to take great pains to avoid that in skatepark construction. Expansion joints are placed in concrete to establish a series of controlled cracks just like you see in sidewalks and driveways. For skatepark construction we strive for as few expansion joints as possible and settle for random hairline cracking to insure the best possible ride.
It is important to stress that modern skatepark construction is a new technology. The best that we can do is to observe and follow existing patterns in this newly evolving industry. Currently, this pattern is to complete construction with a minimum number of expansion joints, which results in random hairline cracking. That is why we build to such high material tolerances. Remember the statement; “we understand that we are making a trade-off, but random hair-line cracking is better than expansion joints and will be kept to a minimum because we are using 4000 psi concrete (as strong as it gets) over compacted fill (3/4 minus) with number three (3/8 inch rebar) as reinforcement.”
Expansion joints are not a pretty sight! Still have those 65mm Krypto's? You're gonna need 'em.
Expansion steel is a galvanized steel forming material designed to serve as a form and screed guide for the pouring of concrete. The expansion steel remains within the cured concrete creating a thin expansion joint. The steel comes in standard lengths and must be cut to the desired length using a composite blade in a worm-drive saw or with tin snips. The expansion steel comes with steel stakes that can be hammered into the ground. The stakes are then screwed or tied with wire to the expansion steel to create a rigid framework. The use of expansion steel in skatepark construction is primarily for flat slabs and other angular constructions such as pyramids, wedges, flat banks, etc. Expansion steel can be purchased at any masonry supply store.
The specific drainage requirements for any given skatepark will be a function of the design and the topography of the site. Drainage will fall into one of two categories, above or below grade. In only the most extreme circumstance (solid rock) will the substrate composition prohibit the use of below grade drainage.
Above grade drainage relies upon gravity and the slope of the park to drain water across the surface of the park and away without drainpipes, etc. This drainage technique is the least expensive approach. However, this technique will tend to control the skatepark design, because the outside edges of the park must remain clear to allow the water to exit the slab and all obstacles must sit above ground. This means that you cannot have bowls, snake runs or other popular obstacles.
If you choose this drainage option, the minimum slope amount in order to effectively drain water away is your best choice. The standard for good drainage is ¼- inch per foot, which is a bit much for a skatepark. The slab can be pitched (sloped) in any direction, or crowned (made higher) in the center allowing the water to run off both sides.
Drain boxes are used when you choose below grade drainage. In most instances it is preferable to cast your own drain box instead of trying to fit a commercially manufactured box to your application. The grates for most commercially manufactured boxes are dangerous to skate on and can be difficult to fit perfectly flush with the concrete, and a smooth fit is what we are aiming for.
Assuming that the drain lines are already in place, cut out a 1 foot long section of pipe at the location where you want to place the drain box. Then dig back another 6 to 8 inches past the ends of the pipe. Fashion a box out of ¾ inch plywood that will fit within the hole and touch the ends of the drain pipe or pipes. The box should extend 8 to 10 inches below the lower edge of the drain pipes to act as a debris trap. This is a place that leaves and other debris can accumulate before entering the drainpipe and clogging the line. With a debris trap, the drain box will only have to be cleaned out about once a year.
Around the top edge of the drain box form build a frame out of 1 x 2 lumber that extends out at least one inch past the form for the drain box. This frame creates a space where the grate can sit securely without falling into the box. Check with a laser transit to insure the drain box follows the slope of the bottom of the bowl or slab. Do not level the box with the surrounding ground. If you do, one side of the box (downhill side) will remain higher than the finished concrete surface. Take your time as this is very important.
When the concrete is poured in around the drain box form, it encases the drainpipes in concrete so that when the form for the box is removed, only the edge of the pipe is visible. After the concrete has cured, carefully remove the form, making any needed repairs. If the bottom of the box was not completely covered with concrete, pour a few more inches into the bottom of the box to finish it.
Once the area is prepared, forms (wood and, perhaps, steel) will be fabricated and placed. Forms contain and guide the poured concrete while it sets (becomes hard). For skateparks, the concrete will be reinforced with steel rods (rebar). Diesel fuel is sprayed onto wooden forms before the concrete is placed to act as a release agent to facilitate clean removal of the forms from the concrete. It is best to keep the ground moist when concrete is placed. Dry ground will draw moisture from the concrete too quickly and will inhibit proper curing. Concrete should not be placed on a hot, dry day. The rapid evaporation of the surface moisture makes finishing the concrete a nightmare, will not allow proper curing and will ultimately decrease the strength of the concrete.
When concrete is added to the forms, the forms are slightly overfilled and the material worked down and into the corners. Spreading the concrete is done with a square head shovel and a muck rake. This step is critical and must be done quickly. Avoid overworking the concrete and trapping air bubbles. Work the concrete only until the forms are filled completely with enough material to being screeding (see below). Don’t worry if the concrete does not look completely smooth, because screeding, floating and finishing is yet to come. Overworking will cause an excess of concrete to rise to the surface. This can cause scaling (see concrete repairs in this chapter).
Once placed and spread the concrete is now ready for screeding. Screeds are guides that make contact with and move across the edges of the forms to shape the surface of the concrete. Typically screeds are flat, but for skatepark construction screeds come in a variety of shapes. The screed is used to remove excess concrete and low spots will be immediately evident. Low spots should be filled immediately and the section then rescreed. Screed about 3 to 4 feet at a time. There is no difference in procedure between screeding flat or curved areas.
Floating the concrete is next. Floating will begin to smooth the surface of the concrete and work a slight amount of water to the top. Use a magnesium bull float. A bull float has a large rectangular blade that pivots at the end of a long aluminum pole. A bull float helps to level the high spots, fill in any voids and forces the aggregate slightly below the surface of the concrete. The bull float is pushed away from you with the front edge raised, so as not to dig into the concrete. The blade is then brought back toward you almost flat. Again, do not overwork the concrete.
Next, you will begin to finish the concrete. Finishing results in a smooth, even surface. The first step in finishing the concrete is to re-float the surface using a magnesium hand float. This process is very precise, because you basically go over every section by hand. Magnesium (mag) floats are very lightweight and will pass easily over the concrete. Floats with an equal radial transition can be used for curved surfaces (see the section on 8-Feet Radius Floats). Finishing the curing concrete will require the use of knee boards. Knee boards are rectangular plastic boards that that are placed on the curing concrete for the finisher to kneel on. The knee boards minimize the disturbance of the concrete underneath by displacing the weight of the finisher over a greater surface area.
Continued finishing includes rounding the outside edge of the concrete. Rounding the edges will prevent chipping when the forms are removed or from heavy impact after curing. Rounding is done with an edging tool. Like the bull float, the edging tool should be slightly tilted upward on the forward motion to prevent gouging the concrete, while the rear of the edging tool should be slightly elevated upon return.
Troweling is the last step of the finishing process. Quality skateparks have a hard troweled finish. Hand trowels are made in various sizes. Generally they have a rectangular blade. Pool trowels are rounded at the corners and, as the name implies, are designed for working the radial transitions of swimming pools. Use pool trowels on radial transitions and whatever type of trowel you prefer on the flat surfaces. During the first troweling the blade should be nearly flat on the surface of the concrete. It is best to use a broad, sweeping arc motion, overlapping each previous stroke by ½-inch or more. Additional troweling, called “burning” is needed for the smooth durable surface of a skatepark. Tilting the trowel slightly during additional troweling will result in an increasingly smooth surface. Always allow some time in between trowelings for the concrete to set up a bit more. Gasoline powered trowels can be rented from equipment rental stores and used for the finishing of large flat slabs. Power trowels cannot be used on curved elements. The same basic principles are used with a power trowel as with a hand trowel. After a few days of curing the forms can be carefully removed. A pointing trowel is used to separate the concrete from the forms. Slide the trowel along the inside surface of the form board.
The concrete should be kept damp and free of traffic for at least 28 days. With the anticipation that surrounds the construction of a skatepark this may be difficult, but the slow undisturbed cure process is critical to keep cracking to a minimum. Although hardened concrete appears to be cured within a few days the appearance is deceptive as the concrete is still quite fragile. At a minimum the concrete should be allowed to cure for 7 days before being used, but we strongly recommend a full 28 day cure daily saturating the area with water in order to keep random cracking to a minimum. We also find that having lawn sprinklers saturating the park during daylight hours actively discourages unauthorized use. Your patience will pay off in the long run.
Bowls and similar transitional elements such as snake runs are quite impressive and are usually the showpiece of any skatepark. They are also the most complex and physically demanding elements to build. You cannot just “wing it” with any aspect of bowl construction. Every step in the construction process must be fully understood and done properly in order to arrive at a suitable result. Other than labor-intensive minor details (grinding high spots, patching, etc), the result cannot be substantially changed by alterations during the later phases of the construction process. The quality of what you end up with will be determined by your attention to detail every step of the way. This guide is written to help you succeed in building world class bowls or other transitional elements. However, the instructions must be followed carefully and accurately. Now is not the time to reinvent the wheel or to take short cuts. Do not take advice from others that this does not sound right or it could be done quicker or better some other way. Save experimentation for your next park. Read this portion of the construction guide and examine the digital photos as many times as it takes for you to understand the entire process from start to finish. Then go out and build a real jaw-dropper.
Almost all bowls and similar elements should be banded with coping. Coping is the edge formed at the junction of the transitional radius (e.g., the uppermost edge of the wall of the bowl) and the surrounding deck. Coping is most generally used to grind the skateboard axle against. The trucks (axle) of the skateboard essentially lock on to the coping and the board and the rider slides along, similar to the way that a train runs along railroad tracks. Adding coping to the park will be a significant expense in the short term. However, in the long run it will add many years to the life of the park and substantially postpone the need for restorative maintenance. Your design will undoubtedly have areas where the placement of metal coping is appropriate. Put it where it is needed. It more than pays for itself later.
Coping to be used for the outside of bowls or other transitional radii should be fabricated (cold rolled) from 1.90 inch outside diameter (O.D.) Schedule 40 tubular steel pipe. Coping on bowls and similar transitional elements should sit proud of the surface of the concrete by 3/8 of an inch. Rebar welded to the back of the coping will lock the coping into the concrete. Coping for spines can be made from single lengths of tube steel or two tubes welded together at the center. Right angles can be coped with angle steel anchored into the concrete with rebar.
Schedule 40 steel pipe is a tough material and must be custom bent to the desired shape by a firm that specializes in pipe bending. Check the yellow pages to find the company nearest you. Begin your search by looking under pipe bending or plumbing. To help save on shipping costs try to purchase all of your coping and other steel elements at the same time. Don’t worry about how long it has been since high school geometry, the fabricators at pipe bending companies are skilled professionals. In most instances they require only a rough sketch with simple measurements in order to calculate the radius and number of pieces of pipe required for your project. Schedule 40 pipe generally comes in standard 20- or 22-feet lengths. Modern bending facilities use computer controlled rolling machines to bend the pipe. As a result of most bending processes a portion of the ends of each piece of pipe remain unbent. This length, usually 1-foot, will have to be cut off each end of all pieces of pipe before the coping is assembled. Ask the bender if this is the case and, if so, ask them to clearly mark these areas for you.
Coping can also be made out of concrete. Concrete coping can be purchased pre-made in the form of pool coping. The trouble with pool coping is that it cannot be set to the tolerances required for skatepark construction (proud of the concrete surface by 3/8 of an inch) and will stick out proud of the junction of the radius and the deck by an inch or more. This is great if you want an element of the park to resemble the conditions found when skating swimming pools, but might prove disadvantageous for inexperienced new school riders. The downside to any type of concrete coping is that it will chip and be abraded away in time and will eventually require replacement or repair.
The pre-bent Schedule 40 tubular steel pipe will arrive from the pipe benders by truck. Check to confirm the radius is correct before unloading. As touched on before, the machinery that bends the pipe cannot bend the entire length, the last foot of material at each end of pipe will remain straight and these sections will have to be cut off. Remember to ask the benders to clearly mark these areas. Any excess material that needs to be removed in order to get the proper radius (marked by the pipe bender) also needs to be removed at this time. As an example, pipe comes to the bender in standard 20- or 22-feet lengths. For coping a 19 feet radius (38 feet in diameter), four lengths of pipe will need to be bent to provide sufficient material to complete that radius. However, only a portion of the fourth piece of pipe will need to be used. The remainder of that piece of pipe, in addition to the straight end pieces on each piece of pipe, is (usually) unneeded excess that must be cut off.
To cut pipe most effectively use a tool called a pipe cutter as the edges of the pipe will match nicely for welding. Pipe cutters can be rented by the day or week at most equipment rental stores. If a pipe cutter is not available, an oxygen and acetylene cutting torch in capable hands will work fine. Follow standard procedure for preparing the material for welding. Make sure that it is clean and free from rust, grease or dirt. Place the pieces as level as possible, match the ends closely and weld all the pieces of pipe together. Do not grind down the welding bead at this time; the coping will be stronger if you leave it. The bead can be ground away after the coping has been hung and the rebar attached. Get enough additional help to move the welded coping in one piece to the location where it will be within the skatepark.
For accurate excavation it will be necessary to build a jig to guide the person operating the excavation equipment. Fabricate the jig from ¾-inch plywood. For large radial transitions, plywood can be purchased in 12-feet long sheets at most lumber yards. Draw a radius equal to the transition desired onto the plywood. Cut out the radius and cut handles into the plywood to aid in moving it around. Place a 2 x 4 across the center of the jig so that a masonry level, when placed on the 2 x 4, guarantees the jig is in the proper position. As material is removed during excavation, place the upper edge of the jig in line with the ground, make sure it is level, and use the curved edge of the jig to determine high or low spots, and remove or add more material as needed.
This first excavation will be somewhat free-hand. A much more exact excavation will be performed after the coping has been set in place. Overall, careful attention must be shown during all phases of excavation as the removal of material beyond what is called for will result in the need for additional concrete. Over cutting by even an inch in a modest-sized park would result in additional concrete costing several thousands of dollars.
Once the coping has been placed, fabricate a metal hanger from a piece of angle steel notched to fit around the outside diameter of the coping. Attach that hanger to the excavation jig with nuts, bolts and washers. After the coping has been set in place and leveled, the jig will hang from the coping to show precisely the amount of material to be removed or added. Excavate carefully and accurately. It will never get any better than what you settle for at this point without costing you more money in the form of additional concrete.
With the coping lying on the ground, mark around the inside edge of the coping with marking paint or dig a line into the earth with a spade. The coping should then be removed to a safe place out of the way of construction. Power excavation equipment such as a back-hoe or track-hoe should be brought into the center or outside edge of the area to be excavated and the excess material (dirt, rocks, etc) taken out. If the material is needed to build up another area for obstacles or other uses it can be taken there at this time. Use an excavation jig to get as close as possible to the final dimensions called for in the design. Be sure to allow for the depth of concrete and any gravel substrate.
Support posts hold the cross members and support steel that will, in turn, support the coping that guides the screeds that forms the bowl walls. So, support posts are very important. It is imperative that these be placed accurately and solidly. It will be easiest if you have a base of at least 16 inches of clean fill in which to place the support posts. Support posts can be made from 4 x 4’s or by cutting 2 x 4’s and nailing them together at a right angle to each other.
Support posts are placed on 3-feet centers from side to side, with 2-feet centers between the posts front to back. The term “centers” means that there is a stated amount of space between the center of one support member and the next. As example, posts set on “3-feet centers” means that there is 3-feet of space between the center of one post and the center of the next post.
Dig the holes for the support posts 16 inches deep and 10 to 12 inches in diameter. The front hole should be one foot from the outside edge of the coping it is to support. The holes can be dug using a manual post hole digger or various mechanical diggers. The posts should be square to one another and plumb. Check to insure this with a carpenter square and level. Place the support posts in the holes and set them in place using concrete. If using pre-mixed bag concrete it will take approximately two bags for every three holes. Allow the concrete to cure completely before setting the cross members.
Be sure to leave a sufficient amount of the support post remaining above the line of the cross members. This will facilitate the removal of the support posts at a later time. It is easiest to remove the support posts with an articulated bucket on the front of a back-hoe or by pulling them out with a logging chain (if the former is not available). It is important when removing the posts to pull them straight up. If you do not remove them in this way you can cause cracking of the freshly poured concrete walls. If you have any concerns about cracking the walls while removing the support posts, take the time to dig them out by hand. Under no circumstances can the posts be cut off and the concrete and embedded wood allowed to remain in the ground. The wood will eventually rot, leaving a void that will lead to cracking or caving.
Cross members should be 4-feet long and cut from 2 x 4’s. The cross member should be placed 4 inches above the finish height of the coping and 4 inches from the outside edge of the coping. Make sure that the cross member is level before attaching it to the support post with 3-inch screws. The use of screws will facilitate the removal and replacement of the cross member, if necessary. There should be at least 3 screws attaching the cross member to each support post. The excess material that sticks beyond the rear support post allows for the attachment of strong-backs (if needed). Do not allow the cross member to stick out further than the outside edge of the coping it is to support or it will get in the way of the screed that controls the spread of concrete later on.
The support steel should be fabricated from 2-inch angle steel. It should have holes drilled so that it can be attached with bolts, nuts and washers along the bottom of the cross members. Do not use lag bolts as they will not hold strongly enough. The support steel should extend forward (beyond the cross member) and end directly above the coping it is to support. Drill a 5/8-inch hole at the end of the support steel directly above the coping. Re-check the tightness of the bolts holding the support steel to the cross members after a few days to insure the stability of the structure.
Take the coping and hang it beneath the support steel using wire. Next, weld a 6-inch long, ¼-inch pan head bolt to the top of the coping directly under the hole in each piece of support steel. The pan head bolt will sit upside-down directly on top of the coping and will protrude through the hole in the support steel. There should be a washer and nut on each side of the support steel. Be sure to place the lower washer and nut on the bolt before welding as it will be impossible after the bolt is welded in place. Loosely tighten the upper nut and proceed to weld pan head bolts at each support steel location until all bolts are in place. Then remove the wire hangers from the coping and allow it to hang freely from the pan head bolts.
With the coping now suspended by pan head bolts from the support steel use a laser transit to make the coping level to the finish grade. This is most easily done with at least two people. Set the laser transit and receiver to the appropriate height (add for concrete thickness) and take a reading off the top of the coping at each support steel attachment point. If the coping is not at the right height use the nut either above or below the support steel to move the coping up or down until it is level. Check to confirm that the coping is level at all support points before tightening both the upper and lower nuts completely. It is advisable to confirm level after the first vertical rebar has been welded to the coping.
With the coping now firmly in place, the excavation jig can now be suspended from the coping in order to confirm that enough material has been removed to allow for the placement of gravel, rebar and concrete. Hang the excavation jig from the coping and proceed to check around the inside of the bowl or similar transitional element, removing all material that remains in the way. Use a square head shovel or mechanical methods such as bobcat or back-hoe, depending upon how much more material needs to be removed. If you are using mechanical methods be extremely careful of the coping and the support system as a great deal of work can be ruined with even a slight nudge from heavy machinery.
Start by marking the coping with chalk or soapstone at 1-foot intervals. For skatepark construction, use number three (3/8-inch) rebar set on one foot centers. There will be a maximum of 12 inches from the center of one piece of rebar to the center of the next piece in all directions. Number three rebar is very malleable. Start by lightly bending some pieces of rebar and welding them vertically to the back of the coping at the marked locations. Do not allow the rebar to stick up above the coping or it will poke out of the concrete when the deck is poured. Be aware that rebar is made from recycled steel that does not provide for the strongest weld and also has a tendency to rust quickly. Prepare the coping and the rebar as per any welding operation by cleaning the material down to bare metal. Continue to attach vertical rebar until the entire bowl is finished. It is unlikely that one piece of rebar will complete a span from one side of any obstacle to the other. In that case tie on additional sections of rebar until each vertical piece of rebar goes across to connect with another piece on the opposite side. Any two pieces of rebar being tied together must overlap by 30 times the diameter of the rebar or approximately 16 inches.
Tie the rebar with standard tie wire or use any other commercially available tying system designed for that purpose such as quick ties. The quick tie system consists of pre-cut wires with loops at each end. The wire is wrapped around the pieces of rebar to be tied together and a tool consisting of a small hook that swivels at the end of a wooden handle is placed within the loops and twisted, tightening the wire. This is the quickest and most efficient method of tying rebar and is the easiest for unskilled volunteers to learn to use correctly.
Starting at the coping, tie pieces of rebar horizontally to the vertical rebar that is already in place. Remember to place it on one-foot centers. Anywhere that the rebar overlaps must be tied as well. Anytime you need to continue a horizontal or vertical run the two sticks of rebar must overlap by at least 16 inches.
It is easiest to make some measuring guides one foot in length out of scrap rebar so that everyone can have one to use. Rebar can be cut with a hacksaw, but this is slow going. For a large job like a skatepark, use a rebar cutter. They can be rented by the day or week at most equipment rental locations. Always leave a 2 inch space between the rebar and the inside edges of all forms. Before pouring concrete raise the rebar 2 inches above the ground with rocks or pieces of broken concrete block so that the rebar will be in the center of the finished slab. Make sure measurements are accurate and that everything is tied up well. It is more than likely that an inspector from the city will be by to examine your work before pouring and he or she will check ties.
Few obstacles will present as big a challenge as concrete bowls. The immense amount of sheer physical exertion needed on a pour day should not be underestimated. When it came time to pour the bowls, we contracted with a union concrete contractor to provide us with six concrete finishers for three days. These individuals were paid by the hour, with insurance and taxes covered by the contractor. Expect to pay around $50 an hour. These individuals were in addition to a team of five others that had been involved in the construction (forming) up to that point, and a few other volunteers cleaned the concrete off tools and jigs. Just cleaning equipment is a full-time job, but these volunteers can also assist in other ways throughout the day. Overall, you will need a large team to pour the concrete bowls.
We must mention a word or two about union workers who do concrete finishing. First, they will arrive with their own hand tools. Second, they will arrive on time and be ready for work at 8 a.m. They will not care if you are ready for them or not, and their time clocks will be running. You can generally send the union labor home within one hour without penalty (called on account of rain, etc) except for a transportation fee. After one hour, they will be paid for the first four hours regardless of the time worked over that first hour. Likewise, after five hours of work, they will be paid for eight hours. They are paid by the hour for overtime by rounding up to the next hour. Overtime is usually double (in our case $100 per hour). They will quit promptly eight hours after start or expect overtime pay. Do not expect them to stay around extra time without compensation. They will not. So you want to time things correctly so that they can complete all of the placement and finishing within the eight hour period. Due to the nature of concrete work, they will not take lunch, rather they eat as they can throughout the day.
The upshot to this is that union finishers are, in our experience, extremely professional, especially if they come from a reputable contractor and want to remain working for the company. It is our experience that they will remain on the job for the full day, no matter how difficult things get. Avoid the tendency to just get a bunch of concrete workers together, even if they are finishers, because pouring the bowls for a skatepark is probably the most physically demanding work that any member of the team has done in quite a while. It is not unforeseeable that if you get some loosely knit crew that you will have some walk-offs or no-shows the next day. For the pouring of bowls, you want the best workers that you can find and the best may cost more than usual. Do not scrimp on the labor needed to pour the bowls.
For the St. Helens skatepark, we planned to pour two bowls in three days. The bowls were elongated ovals that were each 55 feet long and 38 feet wide. One bowl was 6 feet deep, the other was 8 feet deep. There was a saddle in the center and a saddle at the end where the small bowl connected to the street course. Between the bowls and the surrounding deck, we needed 132 yards of concrete with a cost of over $5000 dollars a day including labor and materials, but the results were well worth it.
At six o’ clock a.m. on the days of the pours, the team responsible for forming and jigging should be at the site, making sure that the screeds are in place, the rebar is blocked into the center of the forms, and water hoses have been run and are ready. All finishing tools should be gathered. In addition, it is a good idea to have electric power available. Be as prepared as possible for anything and everything. The pump truck should be scheduled to arrive in time for set-up before the union finishers arrive at 8 a.m. Contract with the pump truck company well in advance as they are in high demand during peak times. Try to get a little of the bill for the pump truck donated. Work this angle well in advance of the pour. Expect to pay around $1000 to $1500 a day for the rental of the pump truck depending on the size of the truck.
So the pump truck is there, and the finishers and the rest of the crew are assembled. The first load of concrete should arrive at that time and the driver should immediately begin preparations with the pump truck driver. Specifically instruct the driver of the concrete truck not to add any additional water to the concrete mix without approval.
Now is the time to get everyone, including all of the workers, together to discuss how the bowl will be poured. With the St. Helens project, none of the union finishers had ever done anything like this before, with the exception of two that had some experience with swimming pools. Remember, the finishers are there to do whatever you tell them to do for the next eight hours. You should be prepared to tell them when and where the pour will begin and end, explain how the system works and answer their questions. Overall, this meeting should take no more than fifteen minutes.
The pour is then started by pumping concrete a minimum of two-thirds of the way up the bowl wall. Start up high, concrete doesn’t have any trouble moving downward, but once placed it can only be moved higher with a shovel. If the concrete is of the consistency specified, it will start to stack upon itself up the sides of the walls. Yet, there will be a lot of hand shoveling of concrete to the top of the wall until it finally begins to stay in place. When a section has been filled from top to bottom, the screed is dragged across (see previous sections). When constructing a bowl this requires one worker at the top, one at the bottom and one working in the center of the screed. At this point, some workers will remain to float that section while others working with the screed move ahead. Eventually workers will begin to finish and trowel the area where the pour started and the crew will be dispersed among the various stations of placing, floating, finishing and troweling.
One person will walk around the inside and outside of the bowl determining where high and low spots exist that must be refinished. There must be someone that is responsible for saying “O.K. This is good enough, time to move on.” For you to have the highest quality skatepark possible, this individual must understand the entire process from start to finish and be attentive to detail. He or she must not be afraid to insist on perfection and demand that others insist upon it as well. This person should be familiar with what makes and breaks it when building a skatepark. Chances are this person will all ready have identified themselves by their dedication to the project up to this point. Choose this person carefully.
The rate at which additional concrete trucks are ordered must be determined during the pour. Do not get ahead of yourself with the concrete. It is much better to get the concrete that is all ready placed finished properly than to place more concrete than you can finish just because it is there. If you have to, send the truck with the concrete back. If it is your fault you will still have to pay for it, but you will be able to maintain the quality of the park.
The screed for a transitional wall (or any transitional radius) is fabricated in the same manner as an excavation jig. The standard ratio for most transitional walls is an 8-feet radius. This does not mean 8-feet from the top to the bottom of the curve. It means 8 feet from the center of the circle to the outside edge of the circle. See the section on Drawing a Radius on the Basic Concepts page for further clarification.
If the area to be poured has coping, the screed must be fabricated to move and screed 3/8 of an inch to the inside of the coping. The 3/8 of an inch allows the coping to sit just proud of the surface of the finished concrete. Pay close attention, because coping sticking out more than 3/8 of an inch is more suited to in-line skaters and BMX bikes. Less than 3/8 of an inch leaves a smaller grindable surface for skateboarding. The screed should be made so that it can hang and slide freely upon the coping. To hang the screed use a metal hanger fabricated from angle steel in the same manner as the excavation jig. In many instances you can use the same hanger. When the screed is hanging from the coping, the bottom of the screed should set solidly upon the lower floor form. Handles should be cut along the entire length of the screed near the inside to facilitate pulling the screed along the concrete. The screed must be very rigid to resist flexing when pulled. It is important the screed not flex when being pulled along the concrete. Strengthen the screed by backing it up with welded angle steel across one side and bolting the steel to the screed. When fashioned in this manner the screed will only be about 1-foot wide and fairly lightweight. Using this method, screeds can be fabricated for any radius and height. Always perform a test run with the screed before using it to place concrete.
If the plans for your park call for vertical sections above the curved transitional radius this is added to the top of the screed before cutting it out. The metal hanger is then attached to the top of the vertical section. In these instances the excavation jig must also include the vertical section. Excavate as previously described.
The screed for any curved surface is fabricated in a similar manner to a screed for the transitional walls of a bowl. First build a base of fill dirt and compacted gravel to come as close as possible to the desired shape. Next, decide where to divide the shape so that you will have an upper and lower form for the screed to ride on. Form the area using the procedures outlined in forming straight or curved areas (see Basic Forms for Obstacles section). In most instances, the upper form is at the highest point in the area to be formed. Then, using ¾-inch plywood, mark the plywood with the desired curve. One trick is to cut the plywood fairly close to the shape of the ground. Then with the plywood setting at a right angle to the ground, make a fist around a pencil. With the pencil facing the plywood, drag your knuckles along the ground to trace the shape of the ground onto the plywood. Cut away the excess material at the bottom of the plywood. If you repeat this process, by the third time the plywood will conform to the shape of the ground almost exactly.
Trim the upper portion of the board so that the screed is of an even depth. Attach pieces of wood to the top and bottom of the plywood shape to ride along the upper form (or coping) and lower form, and also serve as handles. Additional handles can be cut or attached to facilitate pulling the screed along the concrete. It is important the screed not flex when being pulled along the concrete. You may have to strengthen the screed by backing it up with welded angle steel across one side and bolting the steel to the board or by laminating additional layers of plywood onto the first layer. Always perform a test run with the screed before using it to place concrete. This method is also used to fabricate curved forms in order to divide obstacles such as acceleration humps or saddles. The method for fabricating a form is identical to fabricating a screed. The only difference is that the form will be attached to the ground with stakes to control and contain the concrete and to guide a screed.
For the pouring of exceptionally tall transitional walls or when the concrete is not stacking up properly because of excess concrete thickness or a soupy concrete mix, support walls can be built with plywood and 2 x 4 support posts. Take a sheet of plywood and attach pieces of 2 x 4 across the center. Place the upper edge of the plywood against the coping and wedge support posts below the 2 x 4’s, angling toward the ground. The support panel should now be self-supporting and will remain in place as concrete is pumped from above between the plywood support wall and the back of the coping. If the plywood support panel is made from ¼-inch material, it will bend around most curves. Remove the support wall after the concrete has set slightly.
Support walls are a last resort, take steps to avoid this issue.
As you may have guessed by now, with a standard 8-feet radius it is impossible to reach some areas of the radial transition for hand finishing without something to support the finisher above the curing concrete. Build a ladder to suspend workers above the curing concrete by ordering a piece of pipe bent at an 8-feet radius. Using additional pieces of pipe, weld horizontal rungs a foot or so apart on the inside of the ladder along the entire length. Next, weld a U-shaped frame for the bottom that allows the ladder to sit one foot above the ground, straddling the rebar and sitting above the placed concrete. The top of the ladder must rest on the coping, so weld another U-shaped frame to come out on both sides of the ladder and rest on the coping. To aide in moving the ladder, attach a handle at the top. In this way, two persons can move the ladder, one at the bottom and one at the top of the ladder. Remember to remove any sharp edges as you can easily cut yourself as you work.
For floating the concrete on radial transitions, fabricate floats with the same radius as the transition. Wooden handles can be purchased at masonry supply stores. The handles are flat, but can be cut at an angle on both sides. Attach a blade of hardboard or phenolic laminate with glue and screws to the wooden handle. This tool will allow the finishers to float the surface of the placed concrete without the gouging that would occur with flat blade floats. Make enough for each member of the crew to have at least one. The 8-feet radius float is in the lower right corner.
When pouring a bowl or other large obstacle, the walls are poured first and the floor poured later. One big danger is that after the concrete has been placed and finished, someone will step on the tied rebar of the floor section before the concrete for the walls has time to set up properly. At best this will call for refinishing of the concrete surface. At worst it can cause a series of cracks that looks similar to a waffle. Neither of these events is desirable.
To avoid this damage you may want to consider covering the rebar with a false floor that protects it when walked upon. To make the floor, break 8-inch concrete blocks (half blocks) into two pieces along the sides with a mason’s chisel and a hand hammer. The split blocks will cover the rebar without touching. Upon these blocks place plywood or other planking.
When constructing free-standing obstacles in skateparks, you must first pour the concrete to form the obstacles and remove the forms. Next, you will pour concrete for the surrounding areas. Constructing the skatepark in this order allows for some feathering of the surrounding concrete up to the obstacle, if necessary. All obstacles found in skateparks are complex combinations of basic geometric forms including circles (radii, curves), triangles (ramps, banks, pyramid sides), and squares and rectangles (fun boxes, stairs, pillars, flat slabs). These shapes may appear basic, but they can be combined into an endless variety of objects and obstacles for skateparks.
We will describe the forming and placement methods required to build these basic free-standing obstacles. First, we will describe single shapes, and then describe increasingly complex combinations of shapes. The construction of all the basic geometric forms will be covered at least once. In this way we hope to avoid the tedious and repetitive re-hashing of what are essentially the same objects in different combinations.
Any obstacle can be broken down into two or more constituent elements that fall into the group of basic geometric forms. Once you know how to form and pour these basic shapes, any desired obstacle can be analyzed, broken down into parts and the construction methods can be determined. However, if you ever have an obstacle in mind that you are having trouble breaking into basic geometric shapes, give us a call. We will be happy to help.
Pouring flat surfaces with straight sides is basic flatwork similar to forming a sidewalk or driveway. Simply concentrate on marking the forms straight, level, and parallel to one another. Getting forms level, parallel, and at the correct height will be easier with some assistance. When attaching forms to stakes use a power screw driver, because nailing is likely to loosen or move the stakes. The use of screws will also make it easier to make adjustments and disassemble the forms. Build a 2 x 4 form along one side to start. For a true 4-inch slab, the 3½-inch boards will have to be set ½-inch above the ground (2 x 4’s are actually 3½ x 1¾). Set guide stakes to outline the perimeter of the park. Stretch a guide string between stakes placed at the edges of the skatepark to demarcate the outside edge of the park. Lay a 2 x 4 on edge with its inner face touching the string line. Drive a stake against the outside edge of the board near one end. Hold the 2 x 4 at the desired height and screw or nail through the stake and into the 2 x 4. If you are using nails place a sledge hammer against the inside of the board to absorb some of the impact of nailing and to keep the board in place. Leave the nail heads exposed to facilitate their removal when it is time to disassemble the forms. Drive all stakes deep enough before attaching them to the form board so that the top of the stake is just below the form board. If this is not possible, cut off the tops of the stakes before placing and pouring concrete.
Next, drive another stake near the other end of the form board making sure that the inner face of the board is still in line with the string guide. Set the form to height and then fasten the stake to it. Match the end of the next form board to the first form board, and stake and fasten it in the same manner. Continue with more form boards until you reach the end of the straight area to be formed. Check the height of the form along its entire length to confirm accuracy. Finally, drive stakes every 4 feet and fasten them to the form boards. For the opposite side stretch another guide string between the layout stakes that describe that side and continue as before. For more information, see the digital photos below.
To form a curved area, drive stakes 1 to 2 feet apart along the line of the curve. In place of rigid form boards attach a strip of ¼-inch plywood or bender board to the insides of the stakes. The strip should be the same thickness as the straight form. Attach cleats to the ends of straight forms so that the curved piece can be fastened flush with the straight form faces. Since the curved form board and the straight form board differ in thickness, a cleat keeps the face of the curved form in line with the face of the straight form board.
Forming a floor combines the principles of straight and curved forming. In forming a floor, the bottom form should be an equal distance from the coping or the edge of the upper form all around or on all sides. In this way the screed hangs from the coping or rides the upper form from above and slides along the lower form below. It is important that the screed consistently and completely contacts both the upper form (or coping) and the lower form. In this way, the thickness and shape of the transition can be controlled accurately. Always perform a test run before placing concrete.
The building of forms to contain concrete is not confined to flat surface areas. Any area that requires the accurate control and placement of concrete will require forming. In many areas within a skatepark, these forms will need to follow surfaces that are not flat, but are curved. Forms can be built to guide a screed across any curved surface. First, build up a good base of fill dirt and compacted gravel to come as close as possible to the shape wanted. Decide where to divide the shape so that you will have an upper and lower form for the screed to ride on. Then, fabricate forms for those dividing lines using ¾-inch plywood. Cut the plywood fairly close to the shape of the ground. Then, with the plywood setting at a right angle to the ground, make a fist around a pencil. With the pencil facing the plywood, drag your knuckles along the ground and trace the shape of the ground onto the plywood. Cut away the excess material at the bottom of the plywood. If you repeat this process, by the third time the plywood will conform to the shape of the ground almost exactly. Make sure that the form is a uniform 4 inches thick (the depth of concrete) by trimming away any excess material from the top. Stake the form to the ground using the method outlined in forming and flat areas with straight sides. Use the same method for the other form, if necessary. Finally fabricate a screed to ride across the upper and lower forms, giving the concrete the desired shape.
A flat bank is a slope along a given angle. Pyramids and wedges are just a few of the obstacles that incorporate flat banks. The angle can vary depending on your needs. In skatepark construction the angle does not have to be very extreme to give an exhilarating ride. Be aware that a sharp drop off from a deck onto a flat bank can cause the underside of the skateboard deck to scrape. Lack of a transitional radius at the bottom of a flat bank (where the bank meets the surrounding surface) can result in a “kink” that can disrupt the ride and decrease speed. This effect may be fine for pyramids and wedges, but can be disadvantageous for flat banks designed to build up speed. However, either way is fine if that is what you want. Our point is to make you aware that you can construct the flat bank for either result in roughly the same amount of time, as long as you know what you want.
The difference in the construction of a flat bank that terminates in an angle (kink) at the bottom and one with a transitional radius is a function of changes to the screed. Either way there will be a wooden upper form (or coping) at the top of the flat bank and a wooden lower form at the bottom. Use the same method outlined for forming flat areas. The flat bank screed rides along these two form guides to smooth out the concrete. For small surface areas (e.g., pyramids, wedges) a 2 x 4 with a wooden hanger at the top and bottom will suffice. For large surface areas you will want a metal hanger at the top of the screed with a handle at the top and bottom to assist in pulling the screed along. If a transitional radius is desired at the bottom, fabricate this from laminated sheets of plywood cut to the desired radius (consider 8 feet) and attach it to the bottom of the screed with screws. You will have to remove some of the flat section of the screed to attach the radius portion of the form. The end result will look something like a candy cane.
The pyramid obstacle and its variations typically consist of four flat bank sides at a given angle rising up to meet a flat deck. Again, the height of the pyramid and the angle of the flat banks are a personal preference and should have been determined during the design process. Start by bringing in fill dirt. Compact the dirt and then cover it with 4 inches of gravel. Next, wet and compact the gravel. The desired result is to get as close as possible to 4 inches (the depth of concrete) from the shape of the finished obstacle. Any additional space will simply eat up more concrete. Since it is very difficult to accurately form a pyramid from dirt and gravel, just get as close as possible. In most instances you will want to place rebar prior to forming up the pyramid.
Form the top of the pyramid using the same procedure that you would use to form up a flat surface. Use a laser transit to insure that the form is even with the finish grade. Place support stakes on the inside of the upper form. Place lower forms along the bottom at an equal distance out from the upper form. For the lower form the stakes will be on the outside. The upper and lower forms are then connected at the corners with additional form boards or (preferably) expansion metal running from top to bottom with the face of the form even with each corner. A flat screed is then used to spread the concrete within each section. If wooden corner forms are used you will have to pour two sides then wait for the concrete to set. After this you can remove the corner forms, pour the other two sides and wait for these sides to set. Finally, remove the upper form boards and pour the top. If expansion metal is used, all four sides can be poured at once and the top can be poured as soon as the sides have set.
Stairs in a skatepark mimic obstacles found in street skating. Stairs will make an interesting addition to any skatepark facility. However, it is worth considering flat banks instead of stairs for a couple of reasons. First, it increases skateable space. Second, it will reduce the likelihood of physical injury. If someone is grinding a rail or jumping a span of concrete it doesn’t make any difference if it is a set of stairs or a flat bank under the skateboard and rider, if they make the trick. However, if the rider does not make the trick there is a big difference between landing on stairs and landing on a flat bank. On a set of stairs there is little if any chance for recovery if the trick does not come off. The question is not whether the rider will wipe out or not, rather how severely. It is your park, so use your own judgment. If you decide you want stairs, here is the basic procedure.
Getting the measurements right for step construction is important for safety and comfort if they are to be used for their intended purpose. For skatepark construction we can bend things a bit. Any step is composed of a horizontal tread and a vertical riser. In general, make the tread at least 11 inches deep (12 is even better) and the riser no more than 7 inches high. The landing at the top of the stairs should extend back a good 6 to 10 feet to allow for proper set-up for tricks.
Begin by taking a measurement from the top of the deck of the stairs. Use a string to stretch a level line from that point forward to where the bottom step will be and measure that vertical distance. This is the total rise of the steps. Now, calculate the individual riser height, tread depth and the total run.
To roughly calculate the number of steps in the obstacle, divide the total rise in inches by 7 (maximum rise) and disregard any fractions. For example; if you have a total rise of 40 inches. Forty inches divided by 7 equals 5.71. This yields 5 steps. Next, divide the total rise by the number of steps to get the actual riser height. Forty inches divided by 5 (steps) equals 8. This means there should be 8 inches of rise per stair. An 8 inch rise on steps is too much. If the actual riser height is more than 7 inches add another step. So, 40 inches divided by 6 (steps) equals 6.66. This means there should be six steps with slightly more than 6½ inches of rise per step. A general rule for tread depth is the tread plus the riser should equal 17-18 inches. Or, the tread equals 17-18 inches minus the height of the riser. In our example; 17 or 18 minus 6.66 equals 10.34 inches or 11.34 inches, respectively. A 12 inch tread is best, so with our example, we are right in the ball park. The number of steps multiplied by the tread depth calculates the run of the steps from front to back. For this example we will split the difference and call the tread depth 11 inches. Multiplied by the 6 stairs, we get 66 inches of run front to back.
Make some forms for the sides of the steps out of ¾-inch plywood. Since you will be pouring the stairs before the slab around them add 4 inches for the depth of the concrete. Mark off the steps according to the tread and riser calculations. At first, mark the steps level and square and then give the tread a ¼-inch pitch (maximum) to the front of each step to allow for proper water drainage. Also angle the riser back from the top edge by up to 1 inch.
Position the forms with the good face of the plywood facing inward. Get the forms tight against the area the stairs will connect to. Make sure each form is at right angles to the area of attachment and plumb to your finish grade. Also, make sure the tread of each form is level side-to-side. Drive stakes on the outside of each form at least every 12 inches. Recheck the form position for accuracy and then attach the stakes to the form using screws or nails. Add sufficient bracing to the forms to support the weight of the concrete. Do not underestimate the pressure exerted by the concrete before it sets, it is substantial. It is always better to have too much bracing than to have some part of the form “blow out” during the middle of a pour.
Cut forms for the face of the risers. Make them long enough to overlap the side forms and the correct height. Nail them to the side forms and add additional bracing near the ends and center. Coat the inside surfaces with diesel fuel so that the forms will release cleanly. Hang sections of rebar tied on 1-foot centers 2 inches below the height of each tread. Suspend these sheets of rebar from the corners of the forms with wire.
When pouring the stairs, pour concrete into the forms slowly up to the height of the tread. Work the concrete slightly with a shovel or muck rake, and tap the sides of the form to eliminate air bubbles. Wait until the first step sets a bit before pouring the next one to make sure that it can sustain the weight of concrete placed above. If there are to be any embedded handrail anchors add them now. Follow the manufactures instructions. Finish the concrete as usual. Trim up the edges of the treads with an edging tool. When the concrete has set enough to hold its shape, remove the riser forms, smooth the faces of the risers and round the junction where the riser joins the tread. After curing, remove the side forms and patch any imperfections.
Most poured walls in a skatepark will be cantilever walls, where both sides of the wall are vertical. Walls up to 5 feet high should be a minimum of 8 inches thick. Walls higher than 5 feet should be a minimum of 12 inches thick. Any poured walls should be centered on a poured concrete footing that is twice the width of the wall and 4 to 6 inches thicker than the wall with a minimum of 12 inches. The purpose of a footing is to distribute the weight of the wall over a greater surface area. This footing is what stabilizes the wall. You can pour the footing without a form into cut trenches free of debris. Always reinforce the wall and footing with rebar. Consult local code for exact building specifications.
Forms for the wall must be strong in order to withstand the substantial pressure of the poured concrete. Build the forms from ¾-inch plywood with 2 x 4 stiffeners at least every 2 feet. Place horizontal stiffeners first, and then nail vertical stiffeners across them. Brace the vertical stiffeners with 2 x 4 strong-backs secured to the ground with stakes. Assemble the forms with screws so that they can be removed easily after the concrete has set. Pour concrete slowly up to the top of the wall. Work the concrete slightly with a shovel or muck rake and tap the sides of the form to eliminate air bubbles. If there are to be any embedded handrail anchors add them now. Follow the manufactures instructions. Finish the concrete as usual. Keep the concrete moist as it cures. After curing, remove the side forms and patch any imperfections. Wait several days before backfilling with earth or gravel if needed.
Fun boxes and similar obstacles are some of the easiest to form and pour. These obstacles are basically combinations of squares and rectangles stacked one on top of another with the occasional flat bank thrown in for variety. Rails can be configured and attached in any way desired. The strength of the forming is most critical. The walls must be strong in order to withstand the substantial pressure of the poured concrete. It is better to go overboard on the bracing than to have a “blow out” during the pour. If desired, the obstacles can be poured solid, but this will use a lot of concrete. It is more economical to build up the substrate with compacted earth and gravel. Some individuals may try to tell you to use hay bales in the center of the obstacle and to pour the concrete around them. Although we have never tried it, we do not recommend this procedure.
Build the forms for the fun box or similar obstacle from ¾-inch plywood. Since you will be pouring the obstacle before the slab, add 4 inches for the depth of the concrete. Position the forms with the good face of the plywood inward. Assemble the forms with screws so that they can be removed easily after the concrete has set. Reinforce the plywood with 2 x 4 stiffeners at least every 2 feet. Place the horizontal stiffeners first and then fasten vertical stiffeners across them. Brace the vertical stiffeners with 2 x 4 strong-backs secured to the ground with stakes. Drive stakes on the outside of each form at least every 12 inches. Be sure the forms are at right angles and plumb, with the tops level. Any number of subsequent levels can be formed upon the first level in a manner similar to building stairs. Simply run sections of 2 x 6 across the top of each lower level to support the forming above it. Hang sections of rebar tied on 1-foot centers 2 inches below the top of each level of the obstacle. Suspend these sheets of rebar from the corners of the forms with wire. Coat the inside surfaces with diesel fuel so that the forms will release cleanly.
When pouring the obstacle, pour concrete into the forms up to the height of the first level. Work the concrete slightly with a shovel or muck rake and tap the sides of the form to eliminate air bubbles. Wait until the first level sets a bit before pouring the next one to make sure that it can sustain the weight of the concrete above it. If there are to be any embedded handrail anchors add them now. Follow the manufacturers instructions. When the concrete has set enough to hold its shape, finish the concrete as usual. Remove the forms, smooth the faces, trim up the edges with an edging tool and round the junction where the different levels join.
Acceleration humps, pump-humps or bumps are essentially smooth mounds of concrete placed within the skatepark to be used as free standing obstacles. A saddle is a smooth mound of concrete that typically is a transition between two bowls or between a bowl and another series of elements within a skatepark. The quickest and easiest way to build this type of obstacle is to simply place earth and gravel in the area where the obstacle is desired. Then compact the earth and build a lower form around the substrate as outlined in forming straight and curved areas. The concrete can then be placed within the form to the desired thickness and the surface floated and finished free-hand. However, smoothing large surface areas accurately without a screed is difficult. If you have a large area, the best you can hope for is fair results.
The most accurate method for forming acceleration humps and similar obstacles is to place earth and gravel where the obstacle is desired, and then wet and compact this substrate. After that, divide the obstacle into at least two pieces across the top of the mound, at the highest point. With the division of the mound determined, an upper and lower form can be built using the methods outlined for forming straight and curved surfaces, and forming across radii and curved surfaces. With the form in place, fabricate a screed to ride on the upper and lower forms using ¾-inch plywood.
Fabricating the screed to the correct shape is easy. Cut the plywood close to the shape of the substrate. Then, with the plywood setting at a right angle to the ground, make a fist around a pencil. With the pencil facing the plywood, drag your knuckles along the ground and trace the shape of the ground onto the plywood. Cut away the excess material at the bottom of the plywood. If you repeat this process, by the third time the plywood will conform to the shape of the ground almost exactly. Attach pieces of wood to the top and bottom of the plywood shape to ride along the upper form (or coping) and lower form, and also serve as handles. Make sure that there is a radius at the bottom of the screed where the obstacle meets the surrounding area or the obstacle will have a “kink.” Check to confirm that the screed will also create a fluid curve at the top of the obstacle. Perform a test run with the screed before using it to place concrete. Place and finish the concrete on one side of the obstacle first. Then remove the upper form and place and finish the second side, using the previously placed concrete as the upper form.
Spines attached to one or more sides of a bowl offer a much more interesting element than a standard deck. They are also great as free-standing obstacles. A spine is formed when two identical transitional radii rise from opposite sides to meet at a center piece of coping. The coping can be either a single piece of pipe or two pieces of pipe welded down the center. The use of two pieces of pipe allows for a flat area at the spine where it is easier for a rider to “stall” before riding back down the same radius or dropping in on the other side. Use 1.90 outside diameter (O.D.) Schedule 40 tubular steel pipe for spines. Additional pipe must be attached to the spine in order to suspend the coping for the spine above the ground during substrate preparation.
For a spine that is part of a bowl or similar element, the interior of the bowl is first finished. Next, the support system is removed and the excavation continues on the other side. In that instance, the existing coping will guide the excavation jig and the transitional radius screed from above, and ride on a wooden form board below.
To build a spine as a free-standing obstacle, weld metal legs to the spine that will allow it to set level and at the correct height above the ground. After setting the coping for the spine, use the coping to guide an excavation jig, and build up the area with earth and gravel to the proper level. Prepare the earth and gravel substrate as you would for any transitional radius. Do not be surprised if the substrate cannot be placed all the way to the level of the spine. After compacting the substrate, form the lower part of the obstacle using the methods outlined for forming straight and curved areas. Weld rebar vertically to the spine and tie on additional horizontal sections of rebar placed on 12-inch centers just like a bowl wall. A transitional radius screed similar to the excavation jig must also be fabricated to provide accurate placement of the concrete. The screed will slide along the spine from above and will slide along the lower form from below. Test the screed before attempting to place any concrete. If everything is satisfactory, place and finish the concrete in the same manner as a transitional wall.
We describe the construction of a concrete taco to provide an example of how all elements are combinations of simple geometric forms. When the taco is broken down into simple elements, each element has a procedure for accurate construction. These procedures can then be combined to correctly build any obstacle. However, if you have an element that you find is difficult to break into simple geometric forms, give us a call.
A taco or similar obstacle has a radial transition on the front and a flat bank on the back. The two elements rise to meet at a curved piece of coping in the same manner as a spine. So, if we break this type of obstacle down into its constituent parts we can see that the coping will require fabrication and assembly like the coping for a bowl. The coping must have legs in order to be self supporting in the same manner as a spine. Additionally the radial transition in front will need to be built like a bowl wall, and the back like a flat bank. So, in this example at least four separate elements of construction are being combined to begin work on the obstacle. To begin, the pre-bent coping is welded and legs are attached so that the coping is at the proper height, angle to the ground, and is free-standing. Then, earth and gravel are brought in and compacted. The goal is to get as close as possible to the finished form (minus the depth of the concrete). This requires a transitional radius excavation jig for the front. After excavation is complete, lower forms are built around the obstacle on all sides. This combines the principles of straight and curved shaped flat-work forming as outlined in previous sections.
Two screeds then need to be fabricated including an 8-feet transitional radius screed for the front of the obstacle, and a flat bank screed for the rear. To maintain speed and avoid a “kink”, a radius can be added to the bottom of the flat bank screed. In both instances, the screeds will slide along the coping (spine) from above and the wooden form boards below. Always perform a test run before using a screed to place concrete. The concrete for the obstacle is then placed and finished in the manner that each part of the shape dictates. After the concrete has set, the forms are removed and the concrete residue cleaned from the coping.
Unless rails will sit on flat surfaces, always wait to fabricate rails and other metal obstacles until after the concrete has been placed and finished. Whether you are doing it yourself or having the rails custom made it is much easier to take the measurements from the finished concrete and then fabricate the rail than to try to form the concrete surface to fit a rail that has already been built. Steel is the most common material used in the fabrication of rails and similar objects. Steel can easily be primed and painted to prevent rust without much additional expense. Galvanizing the steel to prevent rust essentially doubles the price of the material plus the galvanized layer will eventually grind off. Although beautiful and weather resistant the material for stainless steel rails will cost about ten times the price of steel. However, stainless steel might be considered for a few carefully selected locations.
Rails should be fabricated from a minimum 1.90 outside diameter (O.D.) Schedule 40 tubular steel pipe. For obstacles made out of square stock or similar material the walls of the material should be a minimum of ¼-inch thick. Make sure to grind down all welding beads and remove burrs to make for the smoothest grind and to protect skaters during falls. If the rail is to be subjected to exceptionally heavy use consider adding gussets to any support posts.
The easiest way to attach rails and other metal elements is to drill holes in the finished concrete after it has cured. Bring the fabricated rail or other element to the park and set it in place. Get some help, as this will be easier with at least two people. Next, you mark where the holes will be drilled and then set the obstacle aside. Drill holes into the concrete at the locations marked using a ¾-inch carbide drill bit in a rotary hammer. Both of these items can be rented by the day or week at an equipment rental store. In a pinch you can use a masonry bit in a regular drill, but this will be slow going. The bit will not drill through large aggregate and will wear quickly.
After the holes have been drilled, blow any concrete residue out of the holes with compressed air. Bolts can then be securely anchored into the holes using one of several anchoring compounds available at masonry supply stores. Ask for a recommendation at the store if you do not have a preference. These anchoring compounds are quite tenacious, in many instances the concrete or the fastener will fail before the compound. A minimum of a ½-inch bolt with the head machined off (to fit into the ¾-inch hole) should be pushed into each hole after it is filled with anchoring compound. If possible, set the rail in place now and allow the anchoring compound to cure as outlined in the instructions that come with the product. After the anchoring compound has set, lock washers and nuts can be placed on the bolts and tightened.
Concrete block construction may be necessary for projects that plan to build the skatepark above ground or into a hillside. Also, concrete block assembly may be necessary to build the back walls of free-standing obstacles such as half pipes. A cinder block wall is the quickest and easiest in most instances. For placing concrete block, you will need a masonry hammer, brick trowel, point trowel, joining tool, 4-feet level, tape measure, brick chisel, and mason line.
For block construction a footing is required. The footing prevents shifting caused by normal ground movement and distributes the weight of the wall over a greater surface area. Footings should be made of concrete on firm ground below the frost line. The footing should be a minimum of 12 inches in depth and at least twice as wide as the width of the wall. The footing should be poured on a minimum of 6 inches of compacted gravel. Consult local code before laying the footing. The size of a standard concrete block is 7 5/8 x 7 5/8 x 15 5/8. When working with concrete block work out your dimensions in multiples of 8 or 16 inches. This allows for a mortar joint thickness of 3/8-inch in addition to the thickness or height of the block. In this way, cutting of the concrete block is kept to a minimum. Half blocks are also available for corners.
To begin a block wall, lay a thick bedding of mortar at the corner of the footing using the masonry trowel. This prevents the block from skidding. Lay the corners by placing the first corner block firmly in the mortar bed at the corner. Then butter (spread a layer of mortar) the exposed edges of the block and place the second block in the course (a layer of block is called a course). On the opposite side of the corner, lay another thick layer of mortar on the footing and butter the edges of the block to be placed. As you lay the block, place it firmly against the first block already positioned in order to form a right angle. The outsides of these two blocks should be flush. To confirm this, check with the level or a square. Butter the exposed edges of the block and lay the second block in the course. The mortar joint between the blocks should be 3/8 of an inch. If the thickness of the joint exceeds 3/8 of an inch use the handle of the masonry trowel to tap the block into position.
For the next course, butter the exposed upper edges of the positioned blocks. Lay another corner block to overlap the joint formed by the corner blocks of the first course and continue laying (pyramiding) corner blocks in the same manner to the third or fourth course. Use the level to check for plumb and level. If any blocks are out of position use the handle of the masonry trowel to tap them into place. Move to the next corner and follow the same method. Always work from the corners to the center of the wall, keeping the corners built up higher than the rest of the wall. Avoid spreading mortar too far ahead as it may dry out and lose its holding power before the blocks are placed within the wall. Working two or three blocks ahead is plenty. If the temperature is high you may have to go one block at a time.
String stretched to form a line between the corners of the wall will provide a line guide for straight courses. By pushing gently with the level and tapping the blocks with the masonry hammer, the blocks can be moved into place. For additional courses apply mortar to the edges of the previous course a few blocks at a time, and also apply mortar to the ends of the blocks that will be placed next. Then place the blocks into position. The joint tool is used to strike (smooth) the mortar joint after the mortar has set for a time. When you have layered concrete block within two courses of the top of the wall, use a piece of a sheet of wire mesh to plug the cores (the hollow center of the concrete block). As you finish laying the final two courses fill the plugged cores with mortar. For the greatest strength, rebar can be placed vertically through the holes in the block and the cores filled with concrete. Consult local code for exact requirements.
The stripping of forming and support systems is the direct opposite of how it was placed together. Keep in mind that fresh concrete is still quite fragile and care should be exercised in disassembly. In many instances, the materials can be cleaned and used again for another project. Under no circumstances allow organic material to remain as the inevitable decomposition will leave voids that can cause cracking or caving. Any coping or other metal edging will undoubtedly have concrete residue, which along with the remains of the pan head bolts from the coping supports, will have to be removed. Remove the excess weld and pan head bolts with an angle grinder fixed with a steel grinding wheel. Do not attempt to hammer the bolts off as the impact to the coping will travel through the rebar and may irreparably damage the concrete. Concrete residue can be removed with a die grinder fitted with a wire wheel or the residue can be removed more slowly with a wire brush.
The expansion and contraction caused by variations in temperature as well as erosive factors such as frost and ice will sooner or later cause concrete to crack or break. Repair and maintenance is inevitable, but easy.
If all goes well there should be no need for repairs. However, if repairs are necessary there are several adhesive compounds that work well for cement. One compound is latex cement. Latex cement has two ingredients including powdered cement and latex liquid. These two components are mixed for a quick hardening concrete repair. Another compound, vinyl patching cement, only needs to be mixed with water. Its strength is greater than ordinary portland cement and it is resistant to variations in temperature.
For small repairs, another compound, epoxy cement, works extremely well although it is very expensive. First you mix the resin and hardener and then add the cement. Epoxy cement has the greatest bonding qualities and will bond to almost anything, including steel. Always wear appropriate safety gear when working with any of these compounds. No matter what the repair, approach preparation the same way. The surface to be patched must be very clean. Scrape away any loose or broken concrete. Brush away any dust or debris. Hammer a few masonry nails into the opening to act as anchors. If you are using one of the newer compounds, follow the directions supplied by the manufacturer. If using a portland cement patching compound, be sure the surface you wish to adhere to is thoroughly wet before placing the mixture. After a patch has set up it can be smoothed off with a finishing trowel.
For big jobs, chemical patching compounds are too expensive and difficult to deal with in large quantity. Unless you are repairing a simple crack or chipped corner, use ready mixed concrete. If additional strength is required one of the previously mentioned compounds can be added. Again, preparation is the key to success. Make sure that the area is clean before starting the repair and dampen the area to be repaired before beginning.
If the instructions in this manual are followed carefully the only gaps that should remain in the park are the few expansion joints resulting from the various pours. Whether they are significant enough to worry about is a judgment call that you will have to make. If you decide to fill the expansion joints there is a variety of non-sagging, self leveling fillers that will work fine and can be purchased at masonry supply stores. Most of these materials are applied similar to caulk. If a filler is used, the area to be filled must be completely dry and free of any dirt or debris. Follow the manufacturers directions for application and safety guidelines.
Great pains should be taken to avoid high spots during the placing and finishing of the concrete. Once the concrete has set it will be hard as a rock and only expensive technology can fix it. If you find that you have been left with a few high spots there are two choices. Live with it and allow it to become one of the eccentricities of the park or grind it down. To grind concrete you can use a concrete grinding wheel on an angle grinder or a diamond grinding wheel. Both of these tools can be purchased at masonry supply stores. Be sure to wear a proper respirator when grinding. To avoid doing any of this, find the high spots during the placement and finishing of the concrete and fix the problem at that time.
Low spots (sometimes called bird baths) create problems, because the water does not run off the slab, but pools in spots. This excess water will take longer to dry or must be removed with a squeegee. To level off a low spot, mortar must be added and feathered into the surrounding area. First roughen up the area to be repaired with a cold chisel and hand hammer. Be sure to wear safety goggles. Then completely wet the area with water. Mix epoxy patching compound and a bonding agent to putty consistency. For a small shallow spot use a square trowel to spread the compound level with the rest of the concrete surface. If the spot is wide and deep, apply the compound in layers. Allow the previous layer to cure completely before applying and leveling the next layer. Finish the patching compound to match the existing surface. Follow the manufactures instructions for curing.
Scaling is the flaking or peeling away of the surface of hardened concrete. This may expose the aggregate and lead to loss. Spalls are circular fragments of concrete that have been detached from the area by changes in the weather or a heavy blow. To repair areas like this requires a feathered patch of mortar or patching compound. Prepare the area by brushing away any loose material or dirt and then keeping the area saturated with water. Trowel on a thin layer of epoxy patching compound. Finish in the same manner as a low spot.
Because of the inherent rough treatment that skateparks receive, ends and edges without coping are especially susceptible to breakage. Because of the likelihood of an area being damaged again after repair you must decide if it is really worth patching. If repair is required, begin by chipping away the edge until you have a groove. Be sure to remove all of the damaged concrete. Hammer in a few masonry nails to act as anchors. Sweep away any loose concrete and saturate the area to be patched with water. For a form, use a board the same height as the area to be repaired. Hold the board in place with wooden stakes or bricks depending on where the damaged area is located. Apply a brush coat of runny patching compound into the groove. Before that compound dries fill in the groove with a firmer mix of patching compound. Remove the form board as soon as the patching compound has set and smooth the patch with a square trowel or an edging tool. Follow manufacturer instructions for curing. Be aware that the patched area will not have the structural integrity of the original structure and will certainly chip again.
The budget for a skatepark is often very tight, so use volunteer labor whenever possible. By following leads and doing a lot of networking we were able to get the logging, excavation and surveying for the St. Helens skatepark donated and, in return, provided companies with tax receipts. During the excavation phase a local alternative high school donated the labor from its work crew for about a week. During the final phase of construction we had volunteer crews comprised of skateboarders and middle school math classes tying most of the rebar for the entire park. This saved us several days of paid labor. We, in turn, lectured on the ways in which math was required to design and build skateparks, how it was used specifically in different areas of the park and how focusing on math skills could increase ones job marketability in the future. When you are well-organized and have ten or fifteen motivated individuals you can tie all of the rebar for a moderate sized skatepark in just a few days.
This and other avenues for free labor should be explored by anyone building a skatepark on a tight budget. It is necessary to discuss and decide the extent that volunteer labor can be used during meetings with the contractor before construction begins. You will also have to arrange with the city council (or other group) for insurance coverage of volunteers while they are working on the park. Volunteer labor requires more immediate and active supervision, but will be rewarding for everyone as contractors and skilled laborers learn to value their mentorship role and the youth gain a feeling of ownership of the park. Again, know what you need from someone, be prepared, and then go and ask for it.
Once you get started building the park, you will be amazed at how many people come by to check things out. During the St. Helens project, we found this to be a bit of a problem. In the first place, if someone is not working there is a tendency for kidding around, which is not safe in a construction area. More importantly there is the likelihood that the highly paid workers will start talking to onlookers and slow down, which does not help build a skatepark and can add up to serious money quickly. Faced with the decision of what to do, we considered cordoning off the area and not letting anyone in that did not have a key. We hesitated to do that because it would run contrary to our community-based process. Rather, we adopted a “ten minute rule.” Simply put, if you were here to work as a volunteer you could stay and help as long as you wanted, if you were just looking around you could stay for a maximum of ten minutes then you would be asked to leave. This rule worked very well as the youth and their parents did not feel alienated from what was going on and in many instances they helped with tasks in order to stay longer.
We do need to present some math so that you can estimate concrete volume. Use the following formula to calculate concrete volume:
(L x W x H) divided by 27 equals the number of cubic yards of concrete.
Where: L = length (feet) of area.
W = width (feet) of area.
H = Thickness of the slab (0.33 for a four inch slab). .33 is 1/3 of a foot (4” divided by 12”)
A radius in a skatepark is the length of a straight line that could be drawn from the center of an arced object (an object with a single curve) to the outside edge. A radius is defined as the length of a straight line from the center of a circle to the outside edge of a circle. Laying out a radius is simple. Take a nail or pushpin and place it into a board. Tie string to the nail and measure out a length of string equal to the desired radius. Make a loop in the string at the end opposite the nail and insert a pencil or other writing instrument into the loop. Pull the string taut and draw the circle (radius) upon the desired material.
In most instances, the radius of transitions in skateparks is 8 feet from the center to the outside edge of a circle. Do not confuse this with the running length of the curve from top to bottom. However, nothing is written in stone and other radius lengths can be used as desired. However, your selection of radius length should be based upon an understanding of how this will influence the ride. For example, the Upland Combi-Pool, if we remember correctly, had a 7-feet radius on some transitions. This resulted in an 11-feet wall that felt more like 14-feet. Likewise, the broader the arc (the larger the radius), the mellower the ride.