Rust or brown spots on the surface of an asphalt Tennis or Basketball court are becoming unfortunately very common. These cosmetically undesirable spots and streaks on the playing surface usually do not affect play in the beginning; but do detract from the appearance of the court.
These brown spots are also found on asphalt driveways, parking lots and roadways but they are not as visible as they are on a court. The colorcoating makes the spots stand out. These spots are actually metallic metals called Pyrites (iron). Which contaminate the stone used to make asphalt.
Asphalt allows moisture vapors to go through it. The moisture from rain or leaves accumulating on a court goes through the asphalt making the Pyrite wet. The Pyrite then begins to rust. This rust stain eventually comes to the surface of the court causing the ugly brown spots.
In the early stages these spots are just cosmetically undesirable and do not affect the play on the court. Eventually the rusting aggregate begins to swell and causes small bumps in the court. These bumps will start to effect the bounce of the ball. These bumps typically will pop open creating small holes all over the court.
If the brown spots develop on your court these are a few options to try and make them go away. None of these can be guaranteed to solve the problem.
A few manufacturers of the color coatings have developed a coating with a stain blocker in it to blocks out the stains. New England Sealcoating has been trying them for a few years and has had some success. There is one or two courts it has not worked on. We do not feel we have put it on enough courts to say it works. Most of the courts we have used it on, the appearance has been vastly improved.
In the end it is not the contractor that is at fault but the asphalt plant. The contractor purchasing the asphalt has little or no say about the stone in the mix that is being produced.There are som eways to try and avoid getting these ugly stains from developing on your court. If building a court make sure not to use recycled asphalt. Also find out which asphalt plant the pavement is coming from and find some courts that have been paved in the last few years with this mix. Even then it still not possible to predict if the asphalt will contain the Pyrites. The asphalt plants source of the aggregate may vary from time to time. It is impossible for the producer of the asphalt on the contractor to guarantee that the asphalt will not contain Pyrites.
In trying to slow down the appearance of these ugly brown spots you should be proactive. Do not allow leaves, pine needles, or branches to accumulate on the court. Stop mold or mildew from growing on the court. Wash it off when you see it starting to develop. Remove anything that will keep moisture on your court and keep your court clean.
These are what some rust spots look like: