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Apply Polyurethane to A Deck?

Should I Apply Polyurethane to a Deck?

Selecting a deck stain or sealer is a vital step when finishing your deck or when your deck is in need of being recoated. Wood decks are exposed to severe weather conditions and need to be protected with the correct type of wood sealant.

Peeling Deck Varnish

Peeling Deck Varnish

The best choice for finishing a wood deck is to use an exterior wood stain. A semi-transparent penetrating stain will provide adequate water and sun protection. This type of deck stain will enhance the natural beauty of the wood increasing its appearance.

When refinishing a deck, do not use a varnish or polyurethane coating that films on top of the wood, creating a “shiny” finish. These types of finishes are mainly used for indoor applications and break down easily when exposed to the elements. Rain and harsh UV rays will cause polyurethane to fail quickly, which will subject the wood to weathering. The polyurethane will blister and peel on exterior wood. This will create a nightmare to fix where heavy sanding will be involved in the removal. If you want a clear or natural look to your deck consider a deep penetrating (non-filming) clear deck sealer or better yet a semi-transparent deck stain in a natural tone.

When looking for the right deck stain you will find a large variety of colors. Finding a color like Natural, Cedar, or Redwood in a semi-transparent stain will not hide the wood grain like a solid stain or paint would. This can give your deck the natural look you desire while still giving the wood moisture and UV protection.

Do some research on your deck’s type of wood. Search for colors that will give you the final results you want. Do not apply polyurethane to a deck or it may jeopardize the deck’s beauty and longevity. The outdoor elements are too harsh for polyurethane making it a bad choice for exterior deck use. Keep your deck maintained with the proper choice of deck stain and it will be there for you to enjoy for many years ahead.

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28 responses to “Apply Polyurethane to A Deck?”

  1. Caroline says:

    Does an older deck need some sort of preparation before staining?

  2. debra says:

    i live in a rainy climate and the stain wears off on the horizontal parts of the deck. i'm sanding and restaining today, but wondering if i need to sand it first, is that necessary do you know? i'm using a tinted stain

  3. Codie says:

    I want a wet look or shiny finish to our cedar deck. How can I archive this that will hold up. Obviously poly sounds like a no go..any other sealer to put ontop of the stain or something I can use. We are staining it a dark brown and its a brand new cedar deck. Thanks.

  4. Frank Reynolds says:

    Is there a difference between urethane and polyurethane? This can (solid color composite deck stain) only refers to urethane, but the clerk called it polyurethane. She also claimed it could be used for conventional wood decks and could be painted over with latex paint. This product was applied to a wood deck previously painted with latex. INGREDIENTS: Nepheline Syenite, Long Oil Alkyd Resin, Exempt Mineral Spirits, Long Oil Alkyd, Mineral spirits, Urethane Alkyd resin, Xylene, Proprietary Solvent and Ethylbenzene. This product was discontinued due to "harmful formulation" and deep discounted. I was told it can be thinned with standard paint thinner, and if a coarse surface was desired sand can be added. I expect it to exhibit better longevity than latex coating, which would peel in areas after a year or two.

  5. Bronwen says:

    Hi there. I have applied a dark varnish to my wooden deck, but it hasn't come out as dark as I wanted it. Is there any stain / tint I can apply over the varnish to make it darker?

  6. Jason says:

    I recently installed new T&G pine on a covered porch and used a chocolate covered weatherproof transparent deck stain

    My wife is wanting to put a coat of polyurethane over the stain; not so much for the gloss finish, but rather to protect the wood itself from additional stains (melted popsicles, spilled wine, etc.) Im not convinced this is the best approach, as it may cause the porch to be slippery when wet. I also thought that the stain itself would provide a decent barrier so long as I continue to take care of it each season.

    Thoughts on applying this finish over the stain?

  7. Tom says:

    You mention several times Do Not use poly but you never mention what you should use. Would you recommend an oil base product such as; Sherwin Williams semi transparent cedar deck stain.

  8. Dawn Tarbox says:

    I put a clear coat of stain to my cedar deck and it left a yellow look where the stain overlapped. How do I get rid of the yellow look.

  9. anne hagen says:

    We recently had our wood deck stained and sealed. The company we hired said their seal is mixed in with the stain and is applied in one process. I'm just curious if that sounds right? Also, now that they are finished with our deck, should water continue to soak right into the wood when it rains or should there be more of a beading of the water on top of the deck?

  10. Judy payne says:

    Is there any outside deck stain that looks shiny or wet

  11. Lynn Mucci says:

    Hi , We installed a post and beam covered porch about 10 years ago using western red cedar beams and rails. We were told to just use a varathane clear oil based Exterior finish to seal and protect the wood. It looked fantastic at the time, but the last couple of years, it started to look like your picture in the article above. We tried for nearly a week to sand the wood back to pre-seal, and it just wouldn't come off. So I went to the paint store and they sold me a Benjamin Moore Exterior Stain Remove, which I tried on a portion of the post and beam/railings. It turned the wood dark in the places where there was no stain left, and bubbled up some of the remaining stain. It was a mess. We let it dry and tried to sand it again, but it just will not come back to the same colour. So we thought that perhaps if we used the same product to just go over the wood, it would blend in and look ok….it is still wet, but it looks like it isn't going to work. I am afraid that our only option is going to be to paint the post and beam, which I really don't want to do as it is beautiful Red Cedar. Can you help with some advise?

    • You have to remove and the only effective way of doing this is to continue to sand. Try a belt sander. You might want to hire someone as well. After the sanding, you may need to apply a wood brightener. This will lighten the wood and also remove the dark spots that the stripper left. After all this is done, use a lightly pigmented penetrating stain like TWP or Armstrong Clark.

  12. Christy says:

    Is there any kind of a deck coat/sealant that prolongs the life of the coating, or wood? We are considering redoing our deck with the Poly resin material/poly wood that lasts for life. But I thought I had heard somewhere that there is now some type of a deck coat/sealant that is somewhat similar to the long life of the poly material, so there is not a need to recoat as frequently. Please let me know; maybe I am way off base! Thank you.

  13. Maura says:

    I have used an Exterior Solid Stain on a Pine Floor INSIDE. I'd like to put a top coat of some kind on it. Since this is not exposed to the elements, would a polyurethae coat work?

  14. James says:

    This was great information. I did what you said not to do and the results were exactly what you said would happen. Peeling and blister and now it's to the point the paint I used completely peeled and blistered away from the wood. Now I can just see the bare wood. This was a costly mistake since polyurethane is expensive.

  15. Scott says:

    I rented deck sander at the hardware store. Used 80 grit followed by 120. I use an oil base stain that has to be reapplied about every three years because of a south exposure…nothing will last forever on a deck, if you want to "poly" it, I would use a high quality spar varnish used on boats, but again, you will have to sand it back down and re apply at some point.

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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.