I've built a few boards from 1/2" divinycell H80 and never had an issue with spring back. Two were built with 2 layers of 1/2" (12mm) for total thickness of 1". Just vacuum-bagged the 2 sheets together with thickened (& tinted) epoxy on the rocker table. I have a large vinyl bag and the foam and rocker form all go inside it. The blank is still quite flexible before carbon lamination, it but holds the shape very well. (I found that tinting the resin makes it easy to see the seam, which aids in sanding down the rails as I end up taking them down to about 1/2" thickness.) Other boards were just a single layer of foam with 1/8" (3mm) wood skins. So with multiple layer cores, it's no problem. But even with just a single layer, if you laminate just a single side while on the rocker table, it should hold it's shape very well. 4" (10cm) of rocker over maybe 12-15" of nose, isn't that much to ask of closed cell foam.
These users thanked the author Leelanau for the post:
I've built a few boards from 1/2" divinycell H80 and never had an issue with spring back. Two were built with 2 layers of 1/2" (12mm) for total thickness of 1". Just vacuum-bagged the 2 sheets together with thickened (& tinted) epoxy on the rocker table. I have a large vinyl bag and the foam and rocker form all go inside it. The blank is still quite flexible before carbon lamination, it but holds the shape very well. (I found that tinting the resin makes it easy to see the seam, which aids in sanding down the rails as I end up taking them down to about 1/2" thickness.) Other boards were just a single layer of foam with 1/8" (3mm) wood skins. So with multiple layer cores, it's no problem. But even with just a single layer, if you laminate just a single side while on the rocker table, it should hold it's shape very well. 4" (10cm) of rocker over maybe 12-15" of nose, isn't that much to ask of closed cell foam.
That's pretty much the approach I was going to take, so it's good to know that it will keep the rocker set from laminating the first side. I wasnt keen on the idea of just guessing how much extra rocker to add. Thanks for all the advice
These users thanked the author RichR2 for the post:
Go 3.35mins in
When I was researching heat bending PVC closed cell foam I came across this, that's the shrinkage I was referring to, not that caused by expansion (hot) and contraction (cold).