What should I use?

[rockyroo]

I have a bathroom floor to tile, it had ply down and a flexible adhesive was used, tiles have been taken up, but the flexible adhesive wasn't. 4mm ply was put over the top, as anything else would have made it to high. The floor itself is pretty solied and I was just wondering what the best adhesive to use on it would be, and should I keep the grout lines as narrow as possible to minimise movement, any advice would be very grateful, thanks

[Fred]

Min ply should be 15mm, but 12mm will do. Screwed down every 6 inches. Use flexi adhesive & grout. Silicone around walls & toilet etc.

[Dave]

Should have really pulled the old sub-floor up and started again....

[scottish tiler]

your knee mite actualy go thro the 4mm ply when you knell on it since its not on a flat surface, cant they take the door off and shave a bit of it and use the proper ply wood

[Dan]

I'd consider trying to get up the old ply, the cost of 4mm ply over against the cost of 18mm (minimum BS - marine ply or similar too - some better spec thinner panels available with the same strength now too) would have been comparable considering the latter would have been the correct way and not only that (as not all correct ways are easier and easy on your mind in the future) it would have actually been a far better base to start with generally.

IF you do need to tile it as it is i'd still consider fastflex, something you could have perhaps done directly to the dodgy adhesive covered floor with the right prep.

I don't think you've gained anything here mate. you could have saved the floor 4mm + in height, saved money, saved labour time and done the job with much more pride doing it the right way.

I think. Sorry if it's a bland post.