For glassing thinner quarter-inch or three-eighths-inch flat foam panels used for various floors or closeouts, a choice of resin is available. Usually, a vinyl ester or epoxy would be the resin of choice, as opposed to an isophthalic or orthophthalic polyester resin, which are typically lower quality and have a higher shrinkage rate than the vinyl ester or epoxy resin. Vinyl ester will shrink a little more than epoxy, and epoxy really doesn’t have any appreciable shrink rate.
Prepare the foam core with a coat of slurry first. When glassing one side of the panel using vinyl ester resin, once it cures, you will probably find a slight curve to the panel. This is caused by slight shrinkage in the resin. On the first side, make sure the glass is wet out past the foam edge. When flipped over, the longer, cured, glassed edge can be held down to the table by taping or weighing it down. When the second side is glassed, the same shrink rate should hold the panel flat when cured, assuming it was flat to start. Vinyl ester shrink can be held to a minimum with a lower catalyzation rate, 1% as an accepted minimum.
The same technique is used with epoxy, but the panel will cure nearly curve-free. Flipping over and taping the edge will be used to merely hold the panel in place; therefore, holding it flat for the second-side glassing requires little effort. No appreciable shrink rate means little to no curve after the first side is glassed.
It is always easier to create a larger foam panel than needed and trim to size. This eliminates dry edges and resin on the foam edge of the finished size.
The photos shown are using epoxy on a 2-layer laminate.
A couple of technique notes …
- When glassing the first side, try to wet the glass out carefully past the edge of foam without lots of extra resin. This will eliminate resin drips from creeping under the panel onto the raw foam. If it does creep under, a careful sanding will smooth it out without sanding into the foam. Do not trim this before the second-side glassing. The overage will grab any drips of resin that might find their way off the glass and onto the finished first side.
- When pouring resin out to spread with a squeegee or spreader, pour it in a uniform area and spread in a controlled front, wetting out as you go. Don’t pour an arbitrary pattern all over the panel. This will help you create a nice wet out and be able to apply resin as needed, rather than ending up with a lot of extra resin on the panel that needs to be removed when done. The arbitrary pattern is annotated “NO” in the photos.
Another technique is to build your layups before attaching them to the foam core. This allows you to better control the amount of resin in the cloth. I made layups by fully wetting fiberglass cloth (as many plies as desired) on a sheet of plastic. Once fully wet, you cover the plies with another layer of plastic, then squeegee out the excess resin. From there, remove the plastic sheet off one side of your layup and apply it to your prepped foam. Once applied to the foam, you remove the plastic off the other side and apply your peel ply.
Thanks Zach for this write-up. Always learning good stuff from you. Can you sometime do a follow-up on what foam to use when making a panel as well as what glass is best for the job.
-Merry Chrismas!