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Bubbles in Epoxy

On January 9, 2015, in Fiberglassing, Shop Talk: Tips and Techniques, by Gayle Brantuk

So, you decided to build a boat and do the right thing and coat it with epoxy. But, for some reason, when the epoxy dries there are tiny bubbles all over the surface. There are two common causes of bubbles in epoxy. One, air escaping from newly coated wood. This usually only happens on the first coat, but may occur on subsequent coats if the wood is not sealed with the previous coat. Sometimes the bubbling is minimal, sometimes there are lots of bubbles. Why? It could be because of differences in temperature between wood and ambient air temperature, between wood and resin temperature, when the wood is warm… so it could have something to do with temperature. So, what do you do about it? Lightly sand and recoat. If you are going to fiberglass, lightly sand and fiberglass.

Two. The other cause produces bubbles that look more like foam, that make the resin look milky, and can occur any time you apply resin. What causes it? You do. When you use a roller to apply resin (as we do) you may sometimes roll the roller quickly back and forth in order to wet out a particularly stubborn patch of bare wood or cloth. What you are doing is “whipping” the resin. To correct the problem, drag the surface lightly with a brush. The bubbles may migrate out of the resin on their own, if the resin doesn’t set up too fast, but if the surface is ultimately going to be clear, it’s best to brush them out.

Glen-L stocks three lines of Epoxy. Our proprietary brand, Poxy-Shield ®, System Three SilverTip and MAS Low Tox. We hope you find value not only in the products we sell, but also the thousands of pages of resources for those of you who are or wish to build your own boat.


Your Thoughts?

4 Responses to Bubbles in Epoxy

  1. Douglas Wade says:

    I you epoxy in the morning when the wood is rapidly warming bubbles will form and air expands and leaves the wood but if you epoxy when the wood is at a stable temperature or cooling the problems with bubbles is much less. I have built a Tubby Tug and am currently building an 18 foot electric boat.

    • Chris says:

      The main reason for the bubbles is the resin is being applied in too thick of a layer, and if you are waiting hours for it to go off, you are using too slow of a hardener for the temperature.
      Once you get the layer thinner and use a hardener matched more closely the the temperature conditions, you will not have the problem of bubbles.

  2. Chris says:

    One technique I learned years ago working in a boat yard from a fellow who was an expert at doing fiberglass lay ups, was very simple. Most people attempt to put too much resin on at one time.
    If you want a perfect coat each time, do not use a brush or roller, rather use a squeegee.
    As you squeegee the resin over the cloth or mat, you keep a firm pressure on everything just wetting the material. Yes, the fiber will readily show through, but as you do follow up applications, it builds up the resin and covers the fabric.
    Not only does this make a bubble free surface, it makes for a much stronger finished product.
    Does it take a bit longer, yes.
    Does it give you a much better end result, YES!!
    Does a roller have its place, sometimes, but unless you are doing a huge area, the squeegee is the best way to go. Even if you use a roller, it is best to follow up with a squeegee to level the surface and make the bubbles go away.

    As was pointed out to me, too thick a resin layer is not desirable or as strong as a thinner bubble free layer. When you apply resin, making multiple bubble free layers will give you a superior surface every time.

  3. Marvin Cudd says:

    When fiberglassing with cloth don’t use the tape unless absolutely necessary but cut the cloth on a 45 degree (bias cut). Yes you still have to sand the edges and where you overlap it but it will lay flat and not pucker or pull away from the wood. It works well on fairly sharp keels.

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