I did some quick research on thinning epoxy and using commercial epoxy sealers (which is epoxy thinned with a solvent). I found this very useful article at this link: http://www.seqair.com/skunkworks/Glues/WestSystem/Thinning/Thinning.html Here is an excerpt: "Water resistance of a piece of wood is not enhanced by deep penetration. Wrapping wood in plastic makes a pretty good waterproof seal without any penetration at all. Likewise, an epoxy coating on the surface is more water-resistant than a thinned epoxy coating that has penetrated deeply into the wood because, in most instances, the epoxy thinned with solvent is porous (emphasis added. I remember reading somewhere else that the solvent leaves little holes in the epoxy resin). Figure1. MEE of various combinations of thinned and unthinned epoxy at six weeks exposure to 100% humidity. The USDA Forest Products Laboratory developed the Moisture Exclusion Effectiveness (MEE) test. It is a measure of how much moisture is absorbed by wood when it is continuously exposed to 100% humidity. Higher numbers mean the wood has absorbed more moisture while lower numbers indicate less moisture is absorbed. You can see that epoxy with solvent added is not nearly as moisture resistant as un-thinned epoxy (Figure 1). However, if you need an epoxy coated surface that is less of a vapor barrier, thinning West System epoxy with solvent is a valid way to achieve this." I think I will avoid thinning the epoxy as I build my boat.