The term crack filling is a misnomer. Crack “covering” or “bridging” is actually what takes place. It is impossible to completely “fill” the cracks with standard materials applied at the surface.
All that takes place is closing up the top ½-3/4 inch that you can get materials into and thus just “covering or bridging” the crack. This method actually can highlight the crack and make it more noticeable. We have found this type of crack repair is usually a futile effort and suggest NOT treating cracks as they appear but waiting until a resurfacing takes place. If cracking gets bad enough to be an obstacle to the players or the ball bounce, then deal with these problem spots only. Chasing minor cracking is futile, costly and mostly a waste of time unless you are resurfacing the courts. If you have cracking ¼ inch or less and feel you must treat these use a clear silicone caulk keeping the material within the walls of the crack. Don’t bother trying to paint the caulk, the clear material will be as invisible as possible. If cracking is ½ inch or over then you need a material that sets up a little firmer. There are some good materials available that are applied with a putty knife. Contact me and I’ll hook you up.