Why does my polyurethane get bubbles as I apply it?

I am using foam brushes and applying polyurethane as evenly and slowly as I can. It keeps getting tiny air bubbles in it that I can’t get out. At first I wasn’t worried about it but now i’m on my third coat and you can see where the bubbles were in the previous coat. It shows up as slightly rougher spots. Is this normal?

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9 Responses to “Why does my polyurethane get bubbles as I apply it?”

  • Doug E. Fresh:

    It’s not uncommon for polyurethane to get some bubbles in it while applying. It usually brushes out for me though. I’d suggest getting a normal bristel brush as the foam brush may be your problem. They actually make brushes for polyurethane.

    If that doesn’t work maybe it’s just a poor quality polyurethane. Try a better brand.

  • ?:

    The foam brush holds air, thus releasing when you apply pressure while applying product. Don’t stir the poly with a foam brush and try using less pressure during application.

  • justme:

    Did you get all of the dust particles off of the wood before you did the first coat? I always sand lightly between coats and wipe all the dust off again. I know they say to use it in a well ventilated area but dust particles will blow around. Also make sure you allow for proper drying time between coats. You should be able to get a smooth finish without bubbles.

  • Henry B:

    I’ve had the same problem. Don’t know why the bubbles, here are 2 solutions.1 get close and gently blow on the urethane, the CO2 in your exhale should bring the bubbles to the surface or 2. Use a product by klockit that called eat-a-bubble.I’ve included link below.

  • myxlplyx:

    using a foam brush is most likely the problem.try a good quality poly brush (these days as good as any brush and generally guarantee no fibre loss) and make sure you fully mix but very gently mix paint DO NOT shake tin this will give you bubbles in the paint before you even start.good luck.

  • alan_has_bean:

    1. Your poly is also too thick. Thin it with mineral spirits until it’s thin enough that any bubbles that form come up and pop on their own.

    2. Are you "tipping it off"? After you get a coat brushed on, go back over it VERY LIGHTLY with the tips of the bristles just touching the surface (of the poly, not the wood). This will help level the coat out and pop any remaining bubbles.

    Edit: if the poly is glossy, there is no need to mix it at all. It only needs mixing if it’s satin or flat. And then, stir it, don’t shake it.

  • Ingrid:

    You may want to do a little sanding before you add another coat.


  • Chris O:

    On Alans note – only thin with mineral spirits if it is an oil based poly, if waterborn, use water.

  • cowboydoc:

    Your first mistake is the foam brushes. It may be to late.
    I read all these answers, almost all are down the wrong road, go to the nearest Sherwin Paint store and ask an expert, then you won’t think I’m a smarty pants.

    Your job I’m afraid is on the edge of being shot. The bubbles on the first coat will stay there. You should have stopped there. All salespeople should give this advice "do not use a spong brush" although it is on the can, it’s so small it’s unreadable.

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