C3 Gelcoat Needed on Repair?

[Richard K.]

After making a fiberglass repair, do you have to spray gelcoat over the repair, or will a two-part hard primer surfacer, such as PPG NCP250, do the trick?

Thanks
Rich Kossum

[Tracy C.]

Re: C3 Gelcoat Needed on Repair?

Not familiar with the PPG product you mentioned, but in answer to your question, gelcoat is not a manditory requirement over bare fiberglass.

Most any primer surfacer is fine. I typically like to shoot a base coat of PPG DP50 epoxy over the bare glass because of it's excellant adhesion properties and then lay down a couple coats of a 2 part urethane fast build primer prior to block sanding.

good luck,
tc

[Chuck S.]

Re: C3 Gelcoat Needed on Repair?

Rich, some professionals swear by gelcoat and say the paint won't continue to look nice long without it. After wrestling with this question for years, I finally decided that those recommending NO gelcoat were correct.

There were several reasons for my decision: (1) Gelcoat is incredibly labor intensive...one description is it's like sanding the surface of the moon smooth; (2) the sanding process ruins the originality of the body surface by leveling the natural waves in the fiberglass; and (3) it wasn't used at the factory, so it shouldn't be necessary on a repaint unless the car has been stripped to bare fiberglass and left in the desert sun for ten years (or maybe carelessly stripped using media blasting).

My understanding is that gelcoat should be used if there are individual glass fibers extending from the original body panels or repairs. Gelcoat encapsulates the fibers, allowing them to be sanded smooth and flush with the surface, and preventing them from leaving imperfections in the color coat.

It may depend on how you make your repairs. I make my repairs such that the resin extends beyond the glass mat, and then block sand the repair to feather the repair into the original fiberglass. Once my objective was to make repairs that required no filler...it can be done, but it is incredibly time consuming and work intensive. In any event, there are no loose fibers and I don't think gelcoat is required anymore than the original panels

[Joe C.]

Re: C3 Gelcoat Needed on Repair?

Rich:

The answer depends on whether or not there are any replacement(aftermarket)panels on your car. Some manufacturers expressly forbid the use of epoxy primers. Polyester gelcoat is compatible with original and aftermarket parts, and is specified for use with certain brands of panels.
True, it was not used originally, but IMHO, makes for a much "prettier" job. If you want the original, bumpy surface, then don't use it.

Joe

[Dick W.]

Re: C3 Gelcoat Needed on Repair?

Rich, if the glass is original, I would not worry about problems using the Epoxy products. I prefer PPG DP series, using a color as close to the top coat as I can get. Wonder sealer and a very good substrate to prime or paint over.