Use an industrial grade ( same glues without the price of marine ply).

A/C grade would be fine.
Side one is an A grade smooth good quality finish.
Side two is a C grade, rougher with knots.

If you don't want to cut it yourself the local kitchen makers will often do
it much cheaper than a shipwright.

DP


wrote in message
oups.com...
Would I need to use a special kind of plywood - some "marine" grade or
something? I think that the existing floor is coated with Cetol which
is why I thought that would be the best finish to put on.