Lets not get confused with the reason ply is mentioned in BS for tiling. It is my understanding from what I have read (and no, I don't have a copy of the BS, just read extracts off the net) the ply of minimum thickness 15mm is to be screwed at no more than 300mm centres to strengthen the floor to avoid deflection. If there is no or acceptable deflection and I believe there is a formula for this of L/360 where L is the length of the room, then ply is actually not needed. Now, most people on here will not tile onto chipboard under any circumstances as they believe it is not stable enough and to a point I agree, but if you are tiling a floor of say 2m2 with chipboard, how much movement is there really going to be? Obviously this is a generalisation as I always do a bounce test with the good old glass of water before drawing conclusions, and generally any floor of more than say 2mx2m is starting to get towards dodgy ground. If there is no movement, why use 12 or 18mm ply when 6mm backerboard will the job?
As I have stated in previous posts, if the ply is too thin, I feel it can cause more problems than it solves with the possibility of introducing voids between it and the sub floor. In this case I would prefer to tile directly to the chipboard with appropriate adhesive than risk failure because the two surfaces have gaps between them.
If anyone can provide definitive, written documentation as to why chipboard MUST be overlaid at all cost, please post it up on here so that I can be educated. I am always looking to learn.:yes:
