When a deck is sealed, a protective coating is placed over the wood boards to protect the wood from moisture and debris.  Moisture on untreated wood can lead to several deck problems, including: growth of mold/mildew/algae, dry-rot wood, warped beams, and impaired deck integrity.   

There is a simple and easy test to see if your deck is properly sealed.  Take a hose or a cup of water and pour it onto your wood deck.  If the water beads up into little droplets and sits on top of the wood, your deck is properly sealed.  If you deck drinks the water like it’s a camel in the Sahara, then you have a problem.  You will need to have your deck properly sealed.  Imagine every time it rains or gets wet, moisture is seeping into the wood grains causing expansion and damage to the wood.  Over time if left untreated and unprotected, the wood can grow weak and brittle, becoming become decomposed and eventually break.