If you’re restraining your deck, you’ll need to use a deck stain remover in any case. Pressure washing will not suffice.
Most deck stains will not adhere correctly or penetrate the wood if the previous stain is not removed. In addition, applying a deck stain over an existing stain will peel within a year because the old stain will inhibit the new stain from soaking into the wood as it should.
A deck stripper can break up the damaged stain so that when your contractor pressure washes the deck, the new stain will bind to a good and clean surface.
Your contractor will also recommend using a deck brightener. A brightener’s role is to restore the pH of the wood and open up the grain. A brightener can help open up the wood grains in an older deck or wood fence that have dried up and changed over time. A brightener will aid in the new stain’s absorption and bonding with the grain.