Composite Sandwich foam preparation

I many sandwich boards there is a foam core and foam skins. Most board builders will seal EPS foam with spackle, epoxy and microballons or some other mixture. The principal reason is that EPS has a ton of voids between beads, especially in the lower density ranges. However, it also keeps the resin close to the surface later when laminating. NON-EDRO EPS will absorb liquid and any void from pukas will pool with resin.

This also holds true with most of the high density closed cell foams, except it's just the surface where the cells have been cut open by making a sheet.

I believe that the result will be a more uniform distribution of resin and few if any trapped air pockets that would result in a weakness.

My "wicking agent" is spackle To the left is some unprepped corecell, to the right the prepped corecell ready for lamination.



In this second picture I attempted to show the surface "craters" of the cells opened.

Not great artwork, but I've never been known for that!

A really rough visualization of what the corecell looks like unprepped, laminated in a sandwich without being prepped and then prepped by sealing with spackle. The unprepped foam will end up trapping air and develop uneven resin distribution. Sealing the foam with spackle eliminates the trapped air and creates a uniform absorption rate of the resin, also keeping it closer to the surface for a stiffer board.

Corecell unprepped and before resin:



Corecell unprepped and uneven resin uptake :



Corecell prepped with even resin uptake:

I've been filming & working at the shop for the last 3 months Rock does not use any Spackle on any boards while vac bagging or other wise ,here are some shots of our composite board which is 3 layer sandwich no Spackle or resin is used during the bagging process

No resin? I'd love to hear more about that process.

Neat stuff Jeff!

I assume this is what you were talking about in the Stretch Shop thread?

Yeah - this is the process that Stretch indicated he used. It gets a little weirder in that he never wet's the glass, instead the foam (both sides) receives the resin and the fabric is laid on dry. I'm going to try it and see how it goes. It uses a tad more resin, but should result in a slight stiffer board...probably with less break strength.

Finally hit me - no resin, it's foaming PU glue. I tried GG a few years ago, interesting flex characteristics.

So spreading the resin on the sealed blank was interesting. I was able to easily spread 1.5 oz over the entire surface of the core. The spackle was hard enough and dry enough that the epoxy just flowed across it without issue. It feels like this method would allow a more uniform application of resin and also allow less resin to be used overall.

Laying down the dry kevlar was no more a challenge than laying down wet fabric. In the bag, cooking.