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Can You Apply a Clear Sealer or Polyurethane over a Deck Stain?

Peeling Deck Varnish

Peeling Deck Varnish

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 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.
If you are looking for a more shiny finish on your exterior wood surface, it is best to choose a deck stain that will give you the appearance you are looking for. Applying a clear sealer or polyurethane over a deck stain will cause more problems than it is worth. If you want a clear finish then you can strip off any old stain and start fresh with bare wood. Then you can apply a clear sealer if that is the look you are going for. Just remember that you won’t get any UV protection from a clear sealer only water protection.

In addition, applying polyurethane over a deck stain will make it near impossible to maintain the deck down the road. As the deck stain begins to fail underneath the polyurethane it won’t be possible to clean and recoat it without stripping off all the polyurethane first. So can you apply a clear sealer or polyurethane over a deck stain? It is not recommended and should really be avoided if possible.

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8 responses to “Can You Apply a Clear Sealer or Polyurethane over a Deck Stain?”

  1. wayne asibley says:

    how to apply a wood sealer over another sealer Long story but I am stuck with 12 yr old log cabin and after cleaning
    the 4000 sq fft cabin.I was trying different things I an at a loss Pease advise

  2. Timothy Paints says:

    my client had their front doors stained with twp 100. They would like to add a clear coat over the top to protect it. Is there any option for this application that anyone has had success with? Doors are in a covered patio with morning sun only.

    TWP 100 clear?
    Spar varnish?
    Acrylic Claer?
    Aluminum oxide?

  3. Jim says:

    Power wash my deck in put Thompson water sealer over it had color in it now my girl don't like it she wants to know if she can go over it with stain with sealer on it will it peel

  4. Aimee says:

    I put a clear waterproof sealant on my picnic tables. 3 coats. They are all covered with mold? Can says it fights mold? I pressure washed them and most mold is off. Can I polyurethane them or just do more coats of sealant? Thanks for your help

    • You should never use a polyurethane. Strip off what you put on. Cleaning alone is not enough. Brighten after the stripping. Try the Defy Extreme Clear. It does an excellent job with protection from mold.

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*This is first and foremost a help site from our experience as wood restoration contractors. All stain and prepping manufacturer directions were followed with our reviews and ratings. We offer no guarantee of similar results. Take inconsideration that wood and deck stain results may differ due to prepping procedures, different wood types, exposure to UV radiation, natural weathering, etc.