MAX Update No. 50: How to Make a Fiberglass Mold

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I can’t think of any way to make this brief, or show this but with a stack of photos. If a picture is worth a thousand words, you’re getting 5,000 words’ worth today. Here’s the basics of how to make a fiberglass mold, and how to make a part from a mold.

Starting with the nose pattern in MAX Update No: 48, I gave it three coats of Partall “green wax” mold release wax and covered that with two coats of PVA (polyvinyl alcohol). These mold release agents are standard in the industry, and in theory, either one of them will work. I used both because I really, really didn’t want the mold to stick to the pattern. A blunder here would have set me back a month.

I masked where I wanted the hood to be and then brushed a coat of black gel coat onto the hood area. “Gel coat” is like the paint on molded fiberglass, it conforms to the surface of what you’re molding and then you build the fiberglass part on top of the gel coat. The gel coat and resin are catalyzed plastics; they start off as liquids, then you mix in a catalyst and they harden (“cure”).

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