Deck Defense | This Old HouseDeck Defense. A guide to the cleaners, finishes, and techniques for making your deck look new again. By Fran J. Donegan of Today's Homeowner. Deck Defense. Even if your deck is made of pressure-treated lumber, redwood, cedar, or some other durable species, it's at risk the moment the last nail is driven home. There are several culprits. Moisture swells the wood while the burning rays from the sun dry and shrink it, causing cracks and checks while also encouraging warping.