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

Reader Contribution by Staff
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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”).

Once the gel coat had cured, I laminated three layers of fiberglass mat onto the gel coat, using a polyester resin. The fresh fiberglass (technically FRP, for Fiberglass Reinforced Plastic, but known far and wide as just plain fiberglass) sticks to the gel coat and (knock wood) the gel coat releases from the pattern, giving me an inside-out replica of the hood. To make the mold stiffer and easier to work with, I made a stand for it out of 1/8″ plywood and glued it to the mold with more fiberglass and resin, then gave the whole assembly several days to fully cure.

When I felt brave enough, I popped the mold off the pattern, using wooden paint mixing sticks as prybars (it’s always an act of courage for me–what if I missed a spot with the mold release?). After trimming the edges and giving the inner surface its mold release treatment, I painted it with white gel coat. As you can see in this rare action photo of Yours Truly, my hand is actually moving the paintbrush! This will become the surface of the hood, and once the gel coat cured, I laminated two layers of mat to it.

While I waited for the hood to cure, I cut the fenders free of the nose pattern. There’s no going back now! I positioned the fenders on the car and test-fit the bubble…

Oh yes, as Tom Whitehead commented in Update No. 48, “… if you make the bump in the hood so that it will fit anything you want to stuff in there, so much the better.” Tom, great minds think alike: I made a mold for the bubble so I can bond a bubble to the hood wherever it needs to be — or no bubble at all if I (or somebody else) makes an electric MAX.

So here are all the nose parts, stacked up the way they’ll go. I’ll bond the bubble to the hood with fiberglass, attach the hood to the fenders with Dzus fasteners (removable, so I can check the oil), and attach the fenders to the chassis with…actually, I haven’t figured that out exactly. But I’ve got the parts, now all I have to do is mount them to the car.

Photos by Jack McCornack

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