Seal coat on PVC foam

I don't know much about styrene migration, but I have a mental problrm with diluting polyester resin with styrene to seal the foam to stop syrene migration into the foam. From what I have read vinylester resin would seem to be a useful product for this, but I believe it also has a fairly high styrene content.
Am I worrying about nothing, or is there a better product to use as a first coat on a foam sandwich?

Denny H

[turnershells]

Well, that's pretty close to what I was asking about West Microlight data (and I just got an excellent reply). I'm using epoxy as a filler coat, and I wanted to get some idea of how much weight I can save as I up the percentage of Microlight filler. I'm coating both sides of 1/8" thick airex foam core before bonding 2oz. kevlar to the surface.
Epoxy is more expensive and the stuff I'm using has to be post cured, but there are no volatile solvents. The stuff I'm using is also low viscosity and has a pot life of about an hour. That's pretty much the technique the homebuilt aircraft people use. But they use epoxy as the laminating resin also, so there's no compatibility problems.
If you really want to stick with polyester resin you might try thinning with some Duratec HiGloss to see if that attacks the cores. I use it to spray gelcoat and it's great stuff, no styrene, but you have to find out first what it does to foam.

Regards,

Matt Turner

[JJones]

The priming coat for foam cores is intended to be a barrier to styrene migration. It is promoted or initiated to gel very quickly so that the styrene in the resin gets locked up in the reaction rather than migrating into the core. Vinyl esters will work for priming, but they don't cure well in thin films. However, the mass of the resin in the structural laminate should drive the cure of the priming layer.

Priming is not necessary on many of today's foam cores. However, it does improve the bond strength of the face to the core. Then, the question of 'strongest vs. strong enough' comes up.

Priming also helps on balsa cores, especially when using vinyl ester resins. Balsa has a nominal moisture content of about 12% and that can inhibit the cure of vinyl esters, which are very sensitive to moisture.