On Fri, 13 Aug 2004 18:49:33 GMT, "Calif Bill" wrote:

You do not need Marine Ply. The difference in Marine ply and normal outdoor
ply, is the marine ply will have no interior voids. All the plys are
patched before bonding. No voids is good in a transom, with a big motor
trying to flex the ply. For normal walking surfaces, a standard ACX with
waterproof glue is fine.
Bill

(the following is posted twice in this thread):
I've been told that if I use plywood, unless I use marine grade
it will eventually buckle and swell because only marine grade
is treated in a way which removes all moisture from the wood.
So even if I get a good seal on it, unless I use marine grade
the moister which is contained in the wood will make it swell.
That doesn't really make sense to me since if it's not swolen
when I put it on, I don't see why it would swell later if it doesn't
absorb any more moisture, but two different people have told
me the same thing.