AlexW wrote:
Chris Bacon wrote:
AlexW wrote:

1) What's an appropriate thickness for the board,

3/16", with the outer grain parallel to the existing boards.

OK. What's the logic behind 'llel grains then?

Look at the thicknesses of each "layer" - there will most likely be 3
"layers", one thick in the middle, two thin facings - the thick layer
goes at 90 degrees to the boards, so is less likely to splinter.

2) I have heard talk of wetting down the boards to get them to shrink
a little following fitting ... does this work / is this necessary, as
plywood has long grain runningboth ways which might the effect minimal?

Don't.

OK. Again, what's the logic behind this then?

It's plywood - the layers are bonded at 90 degrees - if you wet it, then
the timber in each "layer" expands much more across the grain, hardly at
all along it. The facings will crinkle and become unstuck (WBP has been
referred to, which is more resistant) - wetting is no advantage, unlike
for paper, or hardboard.

3) Are expansion gaps necessary around the edge (again the plywood
should be reasonably dimensionally stable)? If so what is a suitable
size?

Tiny, 1/8" or 3mm. What are you covering the gaps with?

The comment was applicable to the ply. My intention was to tile over the
gaps (assuming less than say 5mm) with some flexible filler in the gaps
as the edges will not be subjected to any great load. I did this (small
gap though) in my last house on in two bathrooms and it worked fine
(though these were chipboard floors ... latest house is 100+ years older
and the floors are much less dimensionally stable).

I thought you were referring to the ply, in fact...

Any other tips/info would be greatly appreciated.

I have wondered about using 1/8" (3mm) cork sheets in 2'x3'
(600mmx900mm) size for a cork floor. Unfortunately, these are about
£3.50 a go. You might need about 10 sheets. It might look nicer than
the "normal" size.

I'll have a think about that one. Cost is not my prime concern (at c.
£40) ... getting the right result is more important.

Let us know how it turns out if you use larger sheets.. you can see them
in model shops, rolled up like little carpets...