So I'm laying vinyl in a bathroom which is currently just floorboarded. From my research, I understand that I should screw down 5.5mm exterior grade plyboard (exterior grade because of the water) before laying the vinyl which is fine.
My problem lies in actually sourcing this exterior plywood. My understanding is that what makes exterior grade plywood exterior grade is the waterproof glue used between the layers. Yet upon googling, most of the links I am seeing don't mention anything about the glue used, and further state that to be used externally the plywood must be sealed! Seeing this I can't help but think i could buy bog standard plywood and seal it myself to the same effect. So my question is:
Is there anything specific i should be looking for (i.e some standard, or something else)? I've seen the standard EN636-2 thrown around a lot. Ideally the ply should be as cheap as possible, seeing as it won't be visible anyway (will be under the vinyl).
Or can I buy general purpose plywood, and seal it to the same effect?
Best Answer
"Exterior grade" is confusing. The fact is that much of the plywood you encounter already is exterior grade, which (as you've stated) just refers to the adhesive used to bond the plies. It has nothing to do with wood preservation, for example. CDX is the rough grade I'd encounter in the U.S. for this purpose. The 'X' implies exterior adhesive.
Sealing plywood to achieve the same effect probably isn't a good approach. For one thing it'll change how your mortar bonds. For another, it isn't reliable as you'll be puncturing it with a hundred screws.