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Hi,
I have a utility room that currently is tiled on the floor. I need to raise the floor level by about 40mm and then will tile with porcelain tiles. The area is approx 2 x 1 metres.
Should I use layer(s) of flooring grade chipboard or ply, or a layer of chipboard and then ply?
Do I need to fix the flooring through the existing tiles (concrete floor underneath) or can it float?
I assume that as it is a utility room I should use water resistant materials?
Any recommendations on tile adhesive to use?
Thanks,
Gerry

remove the tiles for ease of fixing of the battens, try and use 1" ply or as thick as you can for rigidity of the tiling substrate , alternatively ply with 1/2" and then overboard with Knauf aquapanel 12.5mm which will give you the rigidity of 3/4" ply, the only potential problem is getting the correct rigidity suitable for tiling afterwards, use flexible powder adhesive with a polymer suitable for porcelain and flexible grout after this procedure, hope that helps

Thanks for the quick response and advice, especially the use of aquapanel that I had not considered.
One point I want to check is regarding the recommendation to remove the existing tiles; not just as it would be extra work, but they are solid and secure and as you state, rigidity is the key to a good finish.
So I wonder if it would be better, though initially more difficult to make the first fix, to leave the existing tiles in place, secure 1" ply to the floor (should I use a plastic vapour barrier?) and then overboard with the 12.5mm aquapanel. This will give me the 40mm or so height increase I need and the rigidity?
Is this practical and would I still need flexible adhesive or is a readymix tub OK?
Thanks again.