prep work for loft bathroom

[rachel]

The awful job I posted about a while back has finally been undone today!

The guy who is doing the prep work decided after all to cut all the chipboard. Now comes the question of what to do next.

First he said he would put 18 mm ply. Today he suggested 12 mm + another sheet of 12 mm which our tiler said was a bad idea despite the fact that Fleximat would go on top before the tiles.

Our tiler reckons 18 mm, 22 mm or 25 mm ply. The prep guy says even with additional noggins he won't guarantee the work if he uses 18 mm but he is still happy to do that if that's what we want. Apparently 22 mm is not that easy to find. As for 25 mm it is likely to be a of a problem with height. Fleximat would be used on top of whatever height of plywood we go with.

Any opinions/advice or are we splitting hairs here?

Any advice greatly appreciated here once again. Oh and it's in a small loft bathroom with shower.

[macten]

If height is an issue and the chipboard was solid and deflection free it should have been left in and a 6mm cement board used as an overlay.

Whenever I go straight on to joists I use 25mm WBP ply.

Is the height issue you are concerned about the 'step' into the tiled room?

[Dave]

Lets have this done only 1 more time.. go with the 25mm ply and have peace of mind.

[andy tiler]

Hi rachel take a look at this hope it helps.hopefully ive copied and pasted it properly???
Tiling onto wood - Weber, world

[andy tiler]

As above 25mm ply. putting 2x 12mm sheets together is a no no

[TF Ed]

25mm ply for me too. i wouldnt worry about the extra few mil height issue. better to have that, rather than a failed floor! you might aswell do it properly after all you've beem through