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Old 11-29-2005, 05:28 PM
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JohnW
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Default RE: *Fiberglass (Gel-coated) fuse*

I've done a fair bit of home composite work, making plugs, molds, parts, etc. I've also done a fair bit of research on gel coats, enough to decide It's not worth the smell, mess and headache at home. I've never personally used a gel coat... but I can pass on what I think I know, if ya know what I mean. I can tell you from personal experience that you can produce high quality composite epoxy parts without the gel coat.

From my understanding, with a gel coat, you spray and then lay your first layer of cloth when the gel coal is mid cure, i.e. slightly tacky. Typically when making composites, you never want any layer to fully harden before you apply the next layer. Doing so (i.e. letting a layer fully harden) can create problems with the chemical bond between resin layers. However, this procedure may vary depending upon your layup resin, i.e. epoxy vs. polyester vs. vinylester. I believe there are some compatibility issues between the gels, which are typically polyester. This may limit layup resins and techniques. As for thickness, I believe final thickness can be any depth, but per coat thickness may have issues related to painting if too thick/thin, such as sag, wrinkles, etc. In general, I believe something in the area of 15 mil per coat sounds about right, but I've had a few professional made parts that have a thickness of 1/4" in sharp corners. I assume the gel coat was allowed to pool in these areas to reduce the bend radius such that cloth layup was easier.

Other methods... I've had good luck with straight epoxy. I warm my first layer epoxy to 110F before I mix. This shortens the pot life to about 30 minutes on the epoxy I use, but the epoxy is super thin at this temp. The only defects I get are very small pin holes, and even these are few in number. Of course, you have to finish/paint the part. But you generally need to paint gels too, esp at the seams, and all white is too boring for me so other areas get paint too. Recently, I tried brushing a mold with a thin layer of epoxy as the "gel coat." I had no luck getting this to flow, but I believe it was related to the mold release I was using. I plan on trying that again with PVA release agent or possibly wax only. I'd also like to try a paint in the mold technique if I can find the time. I'd think the paint would act as the perfect model "gel coat." Light weight, finished part, basically flawless, etc.

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