: Air temperature and pressure and wood dimensions change all the
: time. In unsealed wood that creates a constant exchange of air,
: moisture and whatever goes with them in the outer few mm of
: wood. If the surface is sealed but it is less than perfect the
: exchange continues, but at a lower rate, so whatever the builder
: was afraid of is not prevented.

: If you want to seal it helps if the wood is warmed before epoxy
: application; this will make the epoxy more runny and expel some
: of the air from the cells. As the wood cools the epoxy will be
: drawn further into the grain.

: If the objective is to prevent rot perhaps one should ask the
: question, how many kayaks and canoes have died from it? I have
: never seen a ply structure with rot. Outdoor wood structures
: that I have seen don't rot above ground. I have seen lots of ply
: panels that have delaminated, but that is not supposed to happen
: with marine ply. Sealing with epoxy is likely a waste of time
: and money for a dry-moored boat even if it is stored outside.

: My ply sailboat is left outside all year round - it's only in its
: third year so it may be too soon to tell - but so far it shows
: no effects even with only 3 coats of latex house paint.

Actually plywood doesn't change shape much with temperature and humidity changes, though it does increase/decrease in thickness slightly. I still oil them, more because it's prettier that way and does tend to repel some moisture. The oil adds very little to the weight, unlike epoxy which can easily add a couple pounds. I have troubles adding weight to a SOF, lightness is nice :)

Bill H.