How deck finish works All wood has a cell structure just like your body. This is the reason that wood is called "cellular." Its structure is made up of microscopically small cells. No matter As a tree is cut down to make lumber and then cur into the sizes needed, where a board is cut it's surface is made up of cut microscopic cells, which are exposed to mother nature’s elements, the surface will act like a sponge. On a deck, the woods cells are treated with a deck stain, and subject to accumulated air-borne dirt and debris, such as dust and the ever-present tree and plant pollens. Preserving and restoring the natural color of the wood, requires (a.) getting the surface clean, and (b.) applying a good deck wood finish. Subsequent applications, over time, will continue to fill the cells toward the 100% mark. Over-application is to be avoided. For decks, fences, and shakes, etc. a penetrating finish is superior to film forming finishes such as varnish or polyurethane and most water-born finishes, because they do not crack, peel. The application of a good deck finish, actually strengthens the wood fibers. By controlling moistures access, the wood decks dimensional stability is enhanced. Thin applications are recommended, application should be made as often as is necessary. On new work, using standard wood, apply the deck finish immediately, when using pressure treated wood leave wood exposed to the elements for at least six months, depending on exposure and cosmetic appearance. At all times, apply only the amount that the wood will absorb, two thin coats are much better than a thick one.