Thread: Use of Epoxy wood sealers under Polyester resin

You've got it right, polyester doesn't bond well to epoxy, but epoxy does on polyester.

You practice of "sealing" wood with Everdure, just doesn't work, simply put. This stuff isn't waterproof (far from it) so it's use as a sealer is dubious at best. I haven't looked this particular version of penetrating epoxy up in a while by if memory serves me, it's in the 65% - 70% solvents range, which simply means you're not getting much "solids" after the solvents flash off. With few exception all penetrating epoxies have this issue and most are very careful to word their advertising in such a way as to hint it might help waterproofing, but not that it is waterproof. This said, the best waterproofing is straight up epoxy. It can be heated, if you want some penetration, though this isn't absolutely necessary.



What tests have shown is waterproofing (surface sealing) is a function of the coating quality, not amount of penetration. As you can see by the graph, 4 coats of penetrating epoxy is 6 times worst at moisture ingress, then 4 coats of regular epoxy. Even with the addition of regular epoxy over penetrating epoxy, there's very little moisture vapor gain.

All this said, there are things you can add to epoxy to modify it's viscosity, which improves penetration ability. These are referred to as nonreactive modifiers and should be left to those with formulation skills or just a little research in brand contents. BoteCoat is a good choice in this regard, as they use TPRDA type thinners, which seem to work well. Personally, I use the "hot on hot" method, when I desire penetration, which is easier and cheaper.