People often ask what is it that makes the great outdoors so tough on wood. The answer is not really so simple, but the main problem is water. Wood is basically a sponge. It will soak up water, swell up and get soft, just like a sponge. Cappillaries in the wood will transfer the water from the entry point throughout the piece. The water then attracts all the degrading bugs and fungi that will feed on the wood and destroy it. Water also acts as a catalyst in the energetic degradation caused by the sun (described as uv attack). Finally it is water, in combo with the sun that erodes the lignin part of wood and causes the surface to become rough and splintered. What to do if you have a wooden deck that needs protection?
Deck waterproofing is the critical function of any deck refinishing project. Deck coatings need to provide protection against the invasive and destructive nature of water. If you look at your deck after a rain event and it looks darker, then water is doing it's dirty work on your wood. You need to change this.