Updated February 2020
Clear Sealer or Poly over a Deck Stain?
We here at DeckStainHelp.com thank you for your continued support as we continue to be the internet’s number one reference for all things wood deck restoration related. If you have ever considered using a polyurethane coat to give your outdoor wood deck a smooth appearance, read this article and really think about the potential repercussions. As always, we appreciate your input, so feel free to leave a comment below.
Deck stains are meant as a protective finish for exterior wood. They contain special UV shielding pigments and mildewcides to ward off mold and mildew and to keep the wood from fading. Other sealers or clear finishes will not adhere well to a deck stain and may result in the topcoat failing prematurely. Most likely the clear sealer or polyurethane will end up peeling and flaking off the deck stain.
Unlike paint, stains and sealers are not necessarily designed to adhere to each other. Most are designed to penetrate into the wood or at least adhere to the bare wood in the case of film-forming stains. Applying a clear sealer over a deck stain is never a good idea. It really won’t help the deck stain or give any added protection more than the deck stain already is. Clear sealers have no pigment and therefore provide zero UV protection. The same goes for polyurethane.