Working with foam, glass and resin

Polyester versus Epoxy

I first thought I was going to use polyester resin on my project. After all, it's in abundant supply in the 'glassing shop, is relatively inexpensive, and kicks off quickly, enabling a number of steps to be accomplished in quick succession.

John said the best way of using polyester resin is to cover the foam first with a "hot" sealing coat; meaning adding extra hardener to make it kick faster. The reasoning is that then there won't be any time for a reaction between the foam and any styrene in the resin. That's my understanding of it, anyway.

So I did that, using unwaxed resin, and when it was hard I put a piece of glass tape on, with an end sticking over the edge with which to pry it off. In that polyester resin test sample, the tape easily pulled off the first layer of resin, the sealing coat, before the tape tore:

For the epoxy test samples I just added glass tape to the foam and wetted it out with the resin. After a good cure, the G2 resin pulled off the foam, taking some of the foam with it, and the tape didn't tear. The West System epoxy wouldn't pull off the foam, tearing the tape instead. I must say, it wasn't a perfectly scientific test, as I hadn't left the same size of tab to pull on in the West sample. But the West sample test was more to check the new batch of resin & pumps, as I had already decided from the polyester/G2 testing to go with epoxy, for more certainty in the bonding.

Cutting the Glassed Foam

I started with a utility knife, then switched to my pocket knife to cut through the 4-oz cloth, finishing off with the utility knife to cut through the foam. This worked great as far as accuracy: I could cut exactly on the line. But it was hell on the hands, and took a long time.

John offered a jig-saw he'd modified to make a shallow cut, with a metal-cutting blade in it, which worked a treat. It was more difficult to cut exactly on the line, but was way faster and so much easier on the hands:

I put some styrofoam blocks under the work to lift it off the floor a bit. The blade extended ½" below the board I was cutting. Above, I'm getting out the second side plank.

Backside Reinforcing

As I was lifting and moving the glassed-one-side foam around—especially the long & skinny side panels—I was ever conscious of the butt joint between the two panels, and made sure to keep them oriented so that when the glassed side was down, the ends were supported. I could just imagine them folding away at the joint. Now I'm ready to put some glass tape on that joint. I sanded a bit of a hollow first, with 20-grit, so that it wouldn't be as visible when the outside gets glassed:

Now I need to wait until Tuesday to get back in there and do some more damage! ;-)