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Old 02-11-2006, 06:29 AM
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New to Fiberglass

I am getting back into building a street rod. All the cars I worked on to many years back were all steel cars. I have purchased a Glass 32 3 Window and want to do as much of the build as I can myself. The body I bought is by Bebop Glassworks and is a very nice one but it still has seems on it from the mold. I don't have any Esperance working with Glass. I take it that I can use fairly heavy sand paper (#80) on a block to knock down the seams as long as I am careful to stay on the seam. I guess then I need to rough up the gel-coat so the primer with grip. I guess that what scares me is how much I can sand on a glass body. I know that some filler will be needed in some places. What type of filler works best on glass? Would epoxy primer be the best to seal body after I get seams sanded off? Any tips would be appreciated.

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Old 02-11-2006, 07:52 AM
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Good scrubbing

Give it a good scrubbing with Dawn dishwashing soap and hot water to get the mold release wax off. then ssand it with the 80/100 grit to give the body some tooth for the primer..yup sand down the mold seams till they are smooth..any fill that you may need can be done with bondo..

Once you are satisfied then shoot your epoxy primer..If you feel the need use one of the High build primers to fill any scratches and sand that before you put the base coat on..

Just be sure and get that wax off tho..

I have tried most all of it and now do what is known to work..
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A good rule of thumb is treat the gel coat just as you would a coat of primer paint. It has virtually the same consistency and working properties as primer. Thus the seams and inevitable waves, dips, and flaws in 'glas bodies should be block sanded out as you would on a fresh primer job on a steel car. Of course, use the sand paper grit that does the job the best - 80 - 100 grit for the rough out and seam removal, progressing to finer grits as the surface is perfected. BIG rule is do not sand through the gel coat! Sometimes it is unavoidable to do this on seams but avoid it if possible on relatively large flat areas. If the gel coat appears to be getting too thin in a spot and you still need to take off more material, stop and lay on your epoxy/hi-build primer and continue perfecting the finish on the primer base just like a steel car.
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Old 02-11-2006, 09:11 AM
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I and friends do a lot of fiberglass boat work. We usually use 120 or 180 grit -- 80 is usually more aggressive than you need. Experiment a little bit, it may save you some sanding.
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Old 02-11-2006, 09:35 AM
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Depending on how large the raised seams are, you may want to begin with an orbital or 'DA' sander with 80-150 grit, again grit depending on severity of the imperfections. Finish with hand blocking.

If you sand through the gelcoat, be prepared to fill pinholes and air voids in the 'glass with filler. Some filler will likely be necessary anyway, I rarely see a perfect 'glass part

I have not found epoxy primer to be needed on fiberglass, since corrosion is not an issue and normal polyester and urethane products both adhere very well to sanded and cured gelcoat and fiberglass resin. BUT, epoxy won't hurt, and some guys just love it to death for every purpose.

Almost any decent brand of polyester filler will work. The general consensus here seems to be that Evercoat makes a very good line of filler products, I use Evercoat's Rage Extreme for most filler applications.

Last edited by crashtech; 02-11-2006 at 09:40 AM.
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Old 02-11-2006, 11:22 AM
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I used to work for a company that made fiberglass car bodies. (I was shop foreman for 10 out of 13 years I was there) We used 36 grit on an air board or a bondo hog (gear driven 8" orbital sander)to file the bigger seam misalignments down. If we got too far into the glass then we filled and blended the low side with bondo. I like the Evercoat rage also, it sands well. Then block the whole thing with 80, then 120 then 180 until straight. The epoxy primer is not needed but you can use it. There are alot of polyester primers that will fill Feather fill is one that we used to use, Poly-lux was another. Duratec has some really good polyesters and vinyl ester primers. Here is one that we used for mold surfacing. (you bodyshop guys should check his stuff out, I use it on all of my one offs)
It is more than adequate to put on a glass car body used as a surfacing primer. That one you can build up to 40 mil in 1 application. (yes .040") You will still want to use the appropriate primer for your paint over that filler stuff. The big issue about going through the gelcoat is that you get into the pores of the actual laminate. All you have to do if that happens is make sure that you fill the pores that you open up. If you can get an even 15-20 mil coating of a good polyester, vinyl ester, or epoxy primer you cut your chances of getting blisters later on. One thing you need to do before you get too far is to take a block of wood or hard plastic and rub it on all of the outside corners of the body. Detail lines,eyebrow over the door, door openings etc. Push hard. The idea is to bust through the gelcoat into any large air bubbles just under the surface. When laying up fiberglass it is hard to get into sharp corners so air bubbles are a problem in those areas. When you bust them open just fill them with bondo and finish with the rest of the car. If you don't open them up, on a hot or sunny day the air in the bubble will expand and they will look like a little bump. Also when you are sanding and there appears to be an small area that will not sand as evenly as the rest, it may be a bubble. Bust it out. Fill it. Park the body in the sun for a while and look for any little bumps that rise up when the surface is heated. bust em. fillem. The most important thing to remember about fiberglass is the you can't rush the job. Also I wouldn't paint the car a dark color It absorbs too much heat and will make the surface all mottled when it gets hot. It seems like most everyone here is in agreement, there are just a little different approaches to reach the same end. I hope this helps ,mikey
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Last edited by powerrodsmike; 02-11-2006 at 11:31 AM.
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