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Old 07-15-2005, 11:33 PM
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Fiberglass guru's...

Couple questions. ive made a few fiberglass parts but none that were big external parts of the car.. im making a widebody kit for a 1995 bmw m3.. now, im using epoxy resin.. does this need a gelcoat so it doesnt shrink up and add texture to the part after its painted? i always epoxy both sides of the parts.. so far the gelcotes ive seen are only for polyester resins.. is the epoxy on both sides good enough? of course there will be a filler primer over those and then an epoxy sealer over that.... i just dont want this car coming back with the weave showing through the paint.

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Old 07-16-2005, 12:05 AM
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I am not an expert on fiberglass, but I think gelcoat is mainly used in a mold the first layer for a smooth finish, like on boats, it takes place of paint. Now when doing bodywork on a fiberglass part, if I sand through the gelcoat to bare fiberglass I just put some epoxy primer on it. I don't think gelcoat would be needed. Just sand the fiberglass smooth and straight as you can, put on some epoxy primer to seal and urethane primer for fill and sanding. And if its like most fiberglass parts that I've seen get ready to fill some pinholes. Maybe a fiberglass guru that works with it all the time will give better advice. I personally hate fiberglass parts. I just painted a car that a guy wanted a body kit put on with fiberglass fenders, hood and rear bumper. The hood fit terribly with the rear bumper not much better. Not fun redoing all that to get the stuff to fit.
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Old 07-16-2005, 07:54 AM
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Personally I wouldn't use any gelcoat, epoxy both sides to seal the part well then shoot some polyester primer and sand, apply three more coats of epoxy and then final sand that. Not many people sand epoxy but for a final step/primer surfacer you really can't beat the durable surface and it also offers a good solvent barrier which is needed on glass parts.

A friend of mine did a split window vette with gelcoat and the stuff bubbled all over the place sfter it was painted- what a fricken mess! The gelcoat had exceeded it's shelf life and the store didn't know. The evercoat rep was called in to take a look at the car, the car owner's lawyer got involved, the store and Evercoat both paid for the restriping and repaint on that car.

I don't think I'll ever use gelcoat, no real need for it unless you're looking for a prefected surface straight out of a mold.

Sounds like you've got a fun project there, will you be offering these parts for sale as a kit? Could be some good money for you if no body else has these available. Bob
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Old 07-16-2005, 08:02 AM
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Laminating

There are epoxy finish coatings available that serve the same purpose as gel coat..weave showing and pinholes are evidence of poor laminating technique..when laminatng small metal rollers are used to "roll down" the cloth and resin to get a good "fill" in the cloth and a good resin cloth ratio..pinholes are little air bubbles that got trapped between the mold and the part..

On epoxy parts...these are vacuum bagged which presses the part together and helps with the air entrainment area as well as getting a good fill in the mat and cloth..

The goal of a good laminator is to have a part come out that only needs a bit of scuffing to be paint ready..

All of the information needed is available from a good quality supplier of fiberglass cloth and resins..If your current supplier is unable or un willing to provide the necesary tech support then go find another supplier..

just about all I can say about this..

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Old 07-16-2005, 05:10 PM
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omt is absolutely right, just wanted to add one thing. there are many different types of mat. your first layer or two (on the painted side) should be a chopped strand mat. this has the random strands laying in all directions. the other common type is the weaved. has that tight carbon fiber pattern to it. this type of mat builds strength but should never be used against a surface to be painted because when it gets hot in the sun it will always show the pattern in the paint. if your not using gel then epoxy is fine or poly primer works nice too.
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Old 07-16-2005, 09:34 PM
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Something to add

I keep forgetting this but there are some rollers that are made out of metal and look like little paint rollers..these are used to roll out the mat and cloth and resin when laminating..that helps to get rid of any dry spots and the air bubbles in the laminate..

One can get by with a brush on something small but on larger jobs you are gonna need them..they come in various sizes...

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Old 07-17-2005, 12:18 AM
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Yea i got a few of those laying around.. i havent used them much but i definatly need to now since im making full quarter panels.. ill post pics in a new thread when i start... thanks guys
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