Dave Allyn ) writes:

I almost picked up the luan, mainly for the lighter weight, but the
interior glue threw me. My understanding was I needed to have
exterior glue or the resin could (and probably would) delaminate the
layers. Is that not true? my lumber yard does not carry exterior
glued luan in 1/4" (actually, 5mm)

You need exterior grade plywood. They all use moisture resistant glue
except for the fancy wall panneling. If it's kept inside the store it's
usually not exterior grade. If it's keep outside, even under cover, it
should be exterior grade.

I don't know what kind of meranti or lauan is available in the USA. Here
in Ottawa we just have the underlayment, used to put on floors under
carpteting and vinyl. It has one thick inner ply and two thin outer plys.
You have to look for sheets whith few or no edge voids and few face flaws.
I've seen some poor stuff and some excellent stuff. I have filled voids by
drilling small holes through one face ply and pumping in caulk or adhesive
with a caulking gun. That works well. I got one sheet with worm holes in
one face ply which I filled with little drops of polyester resin before
oiling (I use linseed oil on the interior). If I were covering the hull
with fibreglass and resin I would not have bothered.

As I understand it, the only real need to sheath the hull is to keep the
fir plywood from checking and for that you need a pretty thick layer, from
what I've read.

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