Question

how to power wash a deck before staining

Answer 1

Before you apply any type of finish to a wood deck, you must remove any existing finish or there's a good chance your new finish will fail prematurely. It will sit on top of the old finish instead of penetrating, and probably eventually peel off. If you're staining an older deck, you also need to remove the gray surface layer of oxidation if you want the deck to appear anything like it did when it was new. A thorough cleaning of the deck also removes grime, dirt, tannin and rust stains and other blemishes that will show through the finish.