Multiple layers of fiberglass cloth

If you are going to use multiple layers of fiberglass cloth, is better to let the first layer cure before adding the second layer of cloth, or can you apply resin to the first layer, then put the second layer of cloth over the first layer and let them both cure together? My goal is to minimize the chance of bubbles between the layers.

Thank you,



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RE: Multiple layers of fiberglass cloth

Stack everything up and epoxy it all at once.

RE: Multiple layers of fiberglass cloth

That can work very well and is the quickest way to do it, too, but there is risk of bubbles forming. I've had it happen when the wood underneath outgassed and the gas was trapped as bubbles between the layers of glass. Fortunately I noticed this happening before the epoxy had finished curing and was able to work the bubbles out.

There's also the risk of the top layer sliding around on the bottom layer (since fresh epoxy is such a good lubricant), resulting in pockets of epoxy and floating glass, but taking good care to use the minimum necessary epoxy while wetting out will prevent this from happening.

Good luck, 



RE: Multiple layers of fiberglass cloth

Thank you, Fishbuster and Laszlo, for your help.



RE: Multiple layers of fiberglass cloth

A lot of variables weren't discussed:  number of layers, viscosity of resin, weight of cloth/tape, temperature, time available, etc.  If you have fairly thick resin and several layers, it's a real bear to squeegee the resin through the bottom layer without moving the glass around.  I prefer to get the first layer just into the gelled state (not rock hard), trim overhangs and nubs (eg, at darts/overlaps), then carefully go over the entire surface looking for anything that will snag the next layer of glass, smoothing, scraping, sanding as needed.  Repeating for each layer.  (Hopefully I've started on a Friday night and can get back to it over the weekend as time and temps allow.)  If you keep the surface clear of sweat and dust/dirt, you should get a mechanical and chemical bond as good as that from a single layup, possibly with less waste of epoxy.  (Don't ask about the sweat and dirt.)

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