Poptop Lift Bar Went Through Roof!

[DuncanS]

Here is part of the problem. These tops were made using what's called a "chopper gun" process. It feeds fiberglass strands to the nozzle just like a wire feed welder and combined with a sprayer mixes both the resin and hardener right at the nozzle. A rapidly rotating knife chops the fiberglass strands into relatively short lengths and the resulting mix is blown into a female mold. The very early Corvettes and cheap dinghies were built this way. There are several problems in what seems like a good production idea. The first depends on the skill of the sprayer. If he doesn't apply an nice even batch then there can be weak areas. More importantly, the fiberglass strands are too short to be really effective which was one of your failure problems. If a regular lay-up had been done, the strands would have been longer and might have bridged over the damaged area. But even worse, the resulting mat is resin rich. This leads to a brittle structure. The ideal fiberglass composition has just enough resin to wet out the fibers and bridge any tiny gaps between the glass and no more. The strength is in the glass, the resin just keeps them together in the right shape. Although the fiberglass bumpers are molded in a different way with a two part mold, the same problem results because they need the mash to "flow" inside the mold cavity to get a complete part went no external voids.

Expect failure throughout 30 plus year old fiberglass parts. It's par for the course as the resin degrades over time and isn't as strong as it was when new. My 60 year old fiberglass cruising/racing sailboat is still extremely strong as it was properly laid up with separate layers of different types of cloth and was overbuilt.

Duncan

[Vanagon Nut]