The Natural Philosopher wrote in message ...
N. Thornton wrote:
"Graeme" wrote in message ...
"adder" wrote in message
.com...

I'm just aiming for a perfectly flat floor. Without some sort of
filler/levelling compound, the ply will show the undulations that are in
the existing chipboard.


Here's what you do - get a circular saw, cut around the perimeter of
the bathroom floor, buy some WBP ply same thickness as the chip, cut
it to size and install in the hole you created. Job done.

A cunning plan!
Let me think about that one.


exactly. as you said initially you were advised to replace the floor.
The other bodges mentioned in this thread are recipes for trouble.

Expanding foam expands with remarkable force, as I found to my
consternation Sticking it under ply is obviously something the
recommenders have not tried. At least the results would give us all a
laugh

The theory was to leave holes where it could expand upwards, and screw
the ply down firmly first. Its there to support the ply agains flexing,
not to attach it. I have in fact used it so infill gaps between a
flexible meter box and a 12mm plasterboard wall. It did not distort - it
simply oozed out of every orifice, after which it was cut back with a
plaster saw.

Easy peasy, and now that box is rigid, not flexible, and toatlly sealed
agains moistire ingress.

Very different to my own experience. That foam was free to ooze out
too: but it set then expanded, rather than expanded then set. And with
remarkable force!


As for the rest... I assumed the OP meant tiles, not vinyl. Evidently
not though. I wouldnt have any worries about putting vinyl onto a
flexible floor, but real tiles dont work on even slightly bendy
structures.


Regards, NT