On May 23, 7:44*pm, noela wrote:
I am getting set to build an outdoor train layout. *One part of the
layout will be roughly 4'X32' and be built like a deck, flat and
level. *It will be supported on 24" centers. *I am planning on using
3/4" sheets of plywood, and this is where I have my question. *I am
thinking about using Pressure Treated 3/4" plywood sheets, my
reasoning is this: *it will be subject to moisture, and maintaining
it, after I have installed the track over it will be a chore. *I am
looking at a life time of 10-15 years before replacement. *After
reading this thread, I am not sure if I am making the correct choice.
I have selected plywood as it will allow me to maintain a flat and
level surface, rather than use structural wood. *I would really
appreciate any input from this group, even though it sounds as if this
topic doesn't belong here.
Thank you.

Get some good outdoor paint and paint the top and edges real good..
One coat or so on the bottom might be good, You do want the wood to
breathe out the moisture that will get in no matter how much you seal
it... Just do the edges real good, and use good housepaint. If you
really want to do it and keep it for a long time, look into BS1088
rated Marine Plywood. It will last for years with no paint, with paint
and maintenance, 20 years plus...