The Thrower's Page
Repairing and Improving Existing Outdoor Throwing Facilities
Tony Dziepak, 9 Aug 2005
If your shot or discus circle is too rough (as many high school cirlces are), consider rubbing down the surface to make it smoother. First, refer to the outdoor circle construction page to determine if the circle is too rough.
First, try hand-rubbing with a brick-sized block made of cinder block material. A brick made of brick material is too soft and will not smooth concrete. A concrete block will also not work--it has to be cinder. An actual cinder block is too large to work with.
Rub the circle in a circular motion, putting some weight in the rubbing. Rub back and forth all along the circle rim. This is hard work--try to switch hands, or have the throwers take turns rubbing. Wear leather gloves to potect your hands.
Hand rubbing of the circle is very effective in taking down the raw ridges of a brushed-finish circle. Every new circle should be lightly rubbed. Hand rubbing also can take out some unevenness in the circle although if you have depressions, you need to lightly rub these so you don't have spots that are more rough than the high points.
Hand rubbing will not work on a circle in which you have aggregate (stones) exposed at the surface. The stones are too hard to be rubbed down. That's why it is especially important to make sure there is no aggregate near the surface when pouring a new slab.
If you have stones near the surface, you might consider renting a grinder. You will need diamond-impregnated rubbing stones. If there are different grades, get the coarsest grade. The grinder will give the circle a finish similar to terazzo. Do not polish this surface to a marble finish. The grinder is also a good solution to even out an extremely uneven circle.
In the rare case that your circle is actually too smooth (polished marble finish), you might try a muriatic acid solution to roughen the surface. This may be necessary after grinding. I have not tried this. After applying acid for the recommended time, rinse completely and thoroughly with a power washer. I believe you can find muriatic acid at a pool or spa chemical supply store.
Patching means repairing an old circle by filling holes or chunks that have fallen out. To improve the bond, brush the hole with a bonding agent first. Use a premixed patch material. If much of the main part of the circle is patched and the patched surface is more or less rough than the adjacent old surface, you might want to resurface the whole circle.
If rubbing is not possible, you have two options: resurfacing or overpouring. Resurfacing means applying a very thin (skim) coat to create a new throwing surface. If you have a recessed circle, you can resurface the inside of the circle because you are only adding at most 1/8".
Prepare the circle by scrubbing with liquid soap and a metal brush, then rinse completely with a high-pressure hose or power washer until the water runs clear. Dry to damp-dry, then patch holes and uneven spots. Apply a bonding agent to the entire surface. Then apply a premixed resurfacing mix, such as "Top 'n' Bond" or Sakrete concrete resurfacer. The volume is small enough to mix in a 5-gallon bucket. Do not brush this finish--there is not enough depth to do a brushed surface. This surface does not have to be worked. It is an excellent surface.
A #40 bag is enough to do an entire discus circle inside the rim. If you are doing a shot or hammer-only circle, yo umay have enough left over to also do a light coat on the pad outside the rim. Do this after you have smoothed the inside circle, with the remaining mix.
Overpouring means adding 1/2" or more (up to 2") concrete to an old existing circle. Advantages of overpouring is that it is cheaper than pouring a whole new slab, and you can do it yourself with several throwers there to help you mix, pour, and finish. It is feasible to mix enough concrete for an overpour in one wheelbarrow batch; however, you can also rent a portable mixer.
Overpouring is good when you have an old slab that is in the right place, but it may be too low relative to the surrounding ground (allows grass to encroach), or you want to raise the throwing surface in relation to the landing surface.
First, dig a trench around the existing slab, exposing the edge down as far as you need to place a 2x4 even with the height of the new surface.
Scrape off peeling paint and gum from the old surface. Scrub the old surface with detergent and a metal brush. Rinse with a pressure washer or high-power hose.
Place a frame of 2x4s around the old slab. Before putting the frame next to the slab, apply Crisco or other grease to the inside of the 2x4 to keep the concrete from sticking. The 2x4's will be held in place by stakes, the tops of which cannot extend past the top of the 2x4 frame (otherwise they-re in the way during surface finishing).
Level the frame--if the old slab is not level, you can make one side or corner thicker than the other to make it more level, but it shouldn't be less than 1/2" thin at the thinnest point.
Apply a bonding agent. Patch holes. Mix the concrete, and pour into the frame. Distribute it evenly so that it is easier to spread. Spread with hand trowels, then rough level with a straight 2x4 (held upright to avoid bowing) or straight iron pipe screed that is longer than the short side of the frame (this is why the stakes cannot be sticking up past the top level of the 2x4 frame). Make sure there are no air pockets at the edges of the slab.
Then finish with hand floats--do not overwork the surface such that liquid is drawn up. Lightly brush side to side, then go around the edge of the slab with an outside corner trowel.
For any concrete work (resurfacing, patching, and overpouring), the ideal conditions are humid air, 59-68 degrees farenheit. The slab should be kept from drying out as long as possible after pouring--48 hours, if possible. In the summer, the best time to pour is Saturday evening, maybe an hour before sunset, or any day if it is cloudy, cool, and humid, or if you can keep returning to the circle to keep it moist with a mist hose spray. Remember: concrete does not dry--it cures.
After 12 hours, you can just gently pour water on the circle from a gallon jug. Pour it close to the circle--don't hold the jug at waist height.
There are two paths you can take with respect to getting your circle improved. The preferred method is to develop good relations with the high school athletic and activities director, head track coach, and/or throwing coach. Then you may be in the position to suggest or offer to assist in circle improvements. Perhaps your local track club can donate labor and materials in exchange for circle use.
The other option is stealth improvement--where you rub or patch the circle without any official consent. Rubbing is not so bad, and unless the coach is unenlightened, it may be possible to do this on a summer Sunday evening before you throw. It is a little more serious to attempt patching and overpouring without approval. I would do these on a Saturday or Sunday summer evening, but not after dark or else you might raise suspicion. You need to be able to return the next morning to wet down the circle if it is not raining the next day (bring a gallon milk jug of water). You may need to return several times to keep the circle wet. If you are unable to get to the circle to wet it, it could dry and crack in the hot sun. Then you are in a pickle because it is very difficult to remove or re-resurface. The whole thing has to be chipped out. A botched stealth repair is a big problem. I do not recommend a stealth overpour--too risky.
Good luck with your repairs.