: Having recently read the West System manual, they mention that thinning the
: epoxy also reduces it's beneficial properties, so it's probably best to
: use it straight. On Tom's site, he mentions that he coats bulkheads with
: one over-all coat, with an additional coat on the exposed edges, with
: varnish afterwards. And that's on marine ply, so I think you may need to
: do some extra coats on the interior birch ply.

Good call, West System seems to really caution against thinning the epoxy. They offer an alternative:

"There is a better solution to get good penetration without losing strength or moisture resistance. We recommend moderate heating of the repair area and the epoxy with a heat gun or heat lamp. The epoxy will have a lower viscosity and penetrate more deeply when it is warmed and contacts the warmed wood cavities and pores. Although the working life of the epoxy will be considerable shortened, slower hardeners (206, 207, 209) will have a longer working life and should penetrate more than 205 Hardener before they begin to gel. When the epoxy cures it will retain all of its strength and effectiveness as a moisture barrier, which we feel more than offsets any advantages gained by adding solvents to the epoxy."

I have a 500 Watt halogen lamp that should take care of that nicely. As many coats of epoxy as the wood will take plus one and then possibly a coat of something else or paint should keep the wood nice and dry.