Keep your kids safe while playing..You should have your wooden play set professionally power washed, stained, and tightened to help prevent injuries resulting from deteriorating wood and unsafe structures. The sun UV rays break down the surface fibers, causing wood to weaken and turn gray during the process. Rain and snow soak the surface causing the wood to swell excessively, and eventually leading to the breakdown of the internal fibers. Once this happens, the wood becomes spongy and weak. Regular usage and foot traffic will complicate the problem even more.