Painting Fiberglass


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Q. I’m the manager of manufacturing for my company. We are basically a sheet metal fabricator. Recently we added some fiberglass parts to our products. We are trying to paint them on our existing paint line in our plant and are having problems with pinholes and blisters. Do you have any suggestions for painting fiberglass? A. W.


A. Although you didn’t say what form of fiberglass you have, I will try to give you enough information to solve the problem. Painting fiberglass is simple if you know the game.

Most fiberglass and other plastic products have mold release on their surfaces as manufactured. The surfaces must be clean (free from oily soils, mold release and dirt) before painting. If the surface is resin-rich (having a smooth, shiny surface), pinholes should not be a problem when it is clean. If the surface is not resin-rich (having a rough, striated or fuzzy surface), there could be exposed glass fibers. These fibers will act as wicks, pulling moisture into the structure. If your paint line uses aqueous cleaners, moisture can be absorbed by the fiberglass during the cleaning process. The same can happen using solvents during solvent cleaning. The moisture or solvent will come out during the paint curing process and cause pinholes and blisters in the applied coating.

To drive out moisture and solvents, heat the fiberglass to a temperature above the curing temperature of the coating before it is applied. After heating, cool and paint the parts as soon as possible to prevent the fiberglass from absorbing more moisture.

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