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.
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