bobski
Many points with your questions... Silica fills holes and has nothing to do with sealing. It is a filler. The silica is held in place by oil and varnish and that is where the "leakage" comes from. The naptha does little to ease the difficulty in penetration that silica has. It thins the resin(s), oils and waxes that virtually all varnishes (and most "oil finishes") are blended from....
My method involves slow-cure epoxy applied to a warmed stock for a sealer and an oil finish atop that. It is virtually waterproof. Varnishes are only marginal as sealers.
art
