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Painting Fiberglass
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Painting Fiberglass

The Matrix reproduction fenders and side covers are of fiberglass with a polyester resin and made in molds taken from original plastic RL250 parts. The goal was to have fender that has about the same weight and flexibility as an original plastic fender.

Before the mold is used, several coats of release agent are sprayed into the mold to prevent the resin from adhering to the surface. Once set, the parts are removed from the molds, rinsed in warm water to remove the release agent, and trimmed to the final shape prior to shipment.

The polyester resin used is referred to as a surfacing resin because it contains a small amount of wax. The curing process of resin requires it to be excluded from oxygen. Without the wax the resin underneath the surface will cure normally but the surface will not cure and will remain tacky. The wax migrates to the surface and seals the surface allowing all the resin underneath to complete its cure.

It is important that the purchaser, or his painter, take responsibility for the complete preparation of the surface. Fiberglass is a very good lesson in the WYSIWYG (What You See Is What You Get) philosophy. If you can see an imperfection in the surface it will become more evident after paint. Although care is taken to keep imperfections to a minimum there will still be tiny pinholes or small areas where the resin pulled away from the mold surface during cure.

I won't attempt to describe the actual painting process because equipment and materials will not be consistent. If you don't see yourself doing the actual painting maybe the local painter will allow you to prepare the parts and he will just shoot it.

Using spray cans is a choice that you might make but be aware that the paint will never harden to the state that an acrylic enamel paint will and that gasoline and other chemicals will seriously attack the finish.

Fortunately, fiberglass is very easy to work with. Before beginning, assemble the materials that you will need to prepare and paint the part.

bulletSandpapers - a grit around 220 for rough work and 320-400 for finish
bulletGlazing or Spot Putty - tube is available at the local auto parts store
bulletLatex Gloves - available from the auto parts or medical supply store.
bulletWax and Grease Remover - under several brand names from the auto paint store
bulletCheesecloth/lint free cloth - auto paint store
bulletTack wipes - available from the auto parts store
bulletPrimer and paint - an acrylic primer and acrylic enamel top coat is about as simple as it gets for a quality finish. The side covers will require a polyurethane clear coat to protect the decals.
bulletPaint gun/measuring cups/stir sticks/thinner/towels - acquire as needed

Begin by slipping on a pair of latex gloves to keep fingerprints off the prepared part. Thoroughly inspect the surface and note anything that will require attention. Pin hole or voids can be filled with the spot putty. Once dry, the 220 grit sandpaper can be used to break and level the surface left by the parting agent. Remember that you are not trying to remove a large amount of material with the sandpaper. When the process of putty and sanding is complete use the 320 sandpaper to finish.

At this point, I rinse the part off in a sink letting clean water carry away any dust. This will also be the last time to flush away any remaining parting agent. Once dry you are now close to the primer coat. Clean the surfaces completely with lint free cloth and the Wax and Grease remover. You might do this a couple of times as this is the last opportunity to remove the leftover wax from the resin.

If you intend to paint the underside of the part, you will encounter the rough surface of the side away from the mold. It is more difficult to remove the resin wax from the rough side of the part. I use a 1" paint brush with about half the length of the bristles cut off. Work the Wax and Grease remover into the nooks and crannies of the rough texture with the brush several times before applying the primer.  

Use clean and dry compressed air and a tack cloth to remove dust just prior to applying the primer coat. Apply the primer coat in accordance with the manufacturer's recommendations.

Once the primer is dry you will probably see a few more tiny pin holes. These can be filled with the putty, sanded smooth, and another primer coat applied to restore a consistent color. Sand smooth with 320 in preparation for the top coat and go over with tack cloth just prior to applying the top coat. Apply the top coat in accordance with the manufacturer's instructions. Remember to always wear the latex gloves when handling the part.

I allow the top coat to dry completely before applying any decals. A little work with 600 wet-or-dry sandpaper with water prepares the surface very well for both the decals and the clear coat and removes any tiny imperfections. Go over the part with the tack cloth just prior to applying the clear coat. Apply the clear coat in accordance with the manufacturer's recommendations.

Clear coat should be applied to the fuel tank to protect the finish and the decals. The side cover and rear fender decals were not clear coated from the factory but may be if desired.

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Copyright 2014 Matrix Motor Sport
Last modified: 05/26/14