It's important to plan for painting. Not doing so ahead of time can result in the dreaded do-over, familiar to many of us.
So whats to know? Here are a few tips to begin:
- Don't put anything on the underside of the body until you are finished painting the top. Applying bedliner to the underside of the body panels, for example, is a good idea, as it can help muffle sound, cover up any braces, brackets or other work you may have done, as well as resist damage from small stones thrown up by the tires. But applying bedliner, or any solvent-based material before painting risks a damaged paint job. How is that? It's because solvents and other contaminants can migrate upwards to the surface, making primer and paint difficult or impossible to adhere to the body. Another reason to apply paint first is so the undercoating you select can run right up to a painted edge, making the line where paint and undercoating easy, safe and attractive. When you are done painting the exterior of the car, take the body parts you want to coat, flip them over, apply the coating, and reassemble after it dries.
- Don't paint anything until the body fitment is all complete. We've seen cases of other cars that the owner, in attempt to get something done that is evident, has painted the body early in the build process. Don't be that guy. Often, the body needs a little fettling, and in the process things get scratched or damaged. When that happens on an unpainted body, normal paint prep covers any previous damage, and the paint is preserved.
- Decide if you are doing bodywork or not, based on your mods. If you are cutting holes in the front fenders for vents, altering the scoop openings, planning to do minor work to make door fit easier (not necessary, but some people do it to make the door fit process faster), cutting holes in the rear for grilles, etc., you will most likely be painting your car, as opposed to just buffing the gelcoat. If you are painting, it makes caring for the bodywork easier, and less stressful.
- When you prep the body for paint, be certain you have cleaned it completely. One of the most common causes of poor paint jobs is poor or inadequate prep. For fiberglass bodies, that means, among other things, that you clean the body thoroughly, getting all the wax, mold release, and other residue from the mold off, as well as any leftover dirt, tape removal liquids, etc. Follow the paint products manufacturers recommendations for cleaning, including their preferred products. The body really has to be clean!
- Give your body a suntan! No, not you, the car. Putting the entire body (including doors, etc.) out in the hot sun will help any remaining air bubbles to show themselves so you can fix them now (as opposed to after the car has been painted. Did we say "Do Over?"). Some bodies have a lot of small pinholes that need to be addressed if you are painting, and these must all be found, and fixed before the paint stage. How long should the body need to bake in the sun? Depending on the age of the body, the time of year, and the color of the body, as little as 48 hours in the sun, and as long as a couple of weeks may be necessary- it depends mostly on your own circumstances. Dark colors absorb heat better, so adjust accordingly.
- Don't begin body prep until fitment (and the curing above) is finished. Just as you shouldn't try to paint until the fitment is complete, don't start trying to get the body ready with primer, etc., until it is completely cured in the sun.
- Support the body everywhere when you start the prep process. Pressure from the sanding block can actually deform fiberglass bodies, so support the body, preferably on a buck, as it is being worked. That way you are sure that the fitment you worked so hard to achieve stays that way.
- Don't sand through the gelcoat carelessly. The gelcoat is pretty hard, and acts as a sealer. When you sand it away from overly aggressive sanding, it can worsen things by allowing more pinholes to come out. You don't want this. Some people believe you shouldn't wetsand the gelcoat as it might trap water that will ruin paint later. In any case, make sure you treat the gelcoat like a friend. You want to keep it, not grind it away.
- Pick your friends, and stay with them throughout. Good advice, but what we mean here is to select one vendor for all your paint needs, from primer, to paint. That way you are sure that the primer is compatible with the paint, and the clearcoat, and the patching putty, etc. Many have gotten good results using the Tier 1 suppliers like BASF, Sikkens and others, but just as many have achieved great results with relative unknowns. Just pick a vendor you trust, that has a local presence, and go ahead! Avoid the temptation to mix and match here.
Here are some links to other sites that discuss prep for painting fiberglass bodies:
Here's an interesting autobody site with a thread on prep: Autobody 101 forum
Another forum link about the topic: Autobody Store - Paint Prep for fiberglass
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