Hi everyone, I would appreciate a little advice on preparing a bathroom floor for tiling, the area is only 2x2m and feels fairly solid underfoot. I have read lots of good info here but I am a little confused as some threads say you should overboard with a minimum of 18mm ply and then 6mm cement boards, others say the floors can be over boarded using only 6mm thick cement boards with no requirement for the 18mm ply.

Could someone also explain deflection and how to measure it and the minimum requirement before for tiling?

Thanks in advance

The floor needs to be deflection free. What construction is the floor now?

If the floor that is down at the moment (either ply/floor boards or chipboard) is solid and correctly screwed to the joists and not damaged by water and what not then you should be ok to just over board with a cement board. The main thing is to get rid of any deflection in the floor before you over board. If however the floor that is down is not in good shape then it is usually best to remove it and replace with min 15mm ply (correctly fixed to the joists) and then over board this with a cement board.

Plywood floors...

Might be a little more info for you in the link above.

in most cases i use 18mm ply ,15mm ply would be fine over board with cement boards, if this causes you problems because of the height the floor will be after completion , you could remove original floor if poss, then 18mm ply then 10 mm cement board, hopes this makes sense
if you take up old floor you can put extra noggins between joists to strengthen the floor, and thus minimize deflection

The floor construction is floor boards and those which I can see look in good shape. When everything is up will have a better idea. The customer who is a friend is having wetwall fitted, floor tiled and a shower installed to replace the bath and the basin moved.

If existing floor boards are in good order plan is to add extra noggins (belts & braces), refit existing floorboards then overboard with 10mm cement boards. Or if floor boards are not fit for purpose remove them and fit 18mm ply then 10mm cement boards.
Would there be any benefit from fitting "Dural Durabase CI Decoupling and Waterproofing Membrane"? Height shouldn't be a problem (only 3mm).
With regards to the shower area would you tank behind the wetwall?

Thanks again everyone

Sorry hopefully last question, is there a better method of detecting deflection other that walking round the room and watching for movement?

If you are going to take up the floor boards to fit noggins, then I would chuck them out and replace with 18mm ply to be honest. It is never a bad idea to use a decoupling membrane if cost will allow and the same goes for the tanking. If it was my bathroom, I would do both

no more ply for me

Some advice please, my friend is having wetwall fitted over the existing tiles before i tile his floor. He has now told me that there are 2 sets of tiles fixed to the existing walls. The two inner walls are plaster board, not sure what the two exterior walls are, plaster/brick? Anyway would two sets of tiles plus wetwall exceed the weight limit for plaster board/brick? The guy fitting the wetwall says it should be ok but he didnt sound overly confident.

hi jmc,this is not the way to go i would advise your friend of this.

platerboard takes a weight of 32 k per sq m 2 layrs of tiles will no doubt alreadfy exceed that and adding wetwall will do this again.....always best to strip the room and install a fresh

Thanks Kilty, if he wont listen I will ask if I can tile the floor before he fits the walls

Can the wetwall be fixed directly to the timber frame or would you recommend putting up cement boards/new plaster board first?
With the bare exterior walls would there be any benift of fixing 6 mm cement boards prior to the wetwall for insulation? If so would you fix it with adhesive or dot and dab with pink grip or the likes? Any recommendations welcome as it's a mate so don't wont to see him given duff info by this other guy. Thanks

wetwall is fitted with an adhesive suited to whatever make it is...fix plasterboard imo dont just stick it to a timber frame

A little more help needed..........

When fixing the cement board to the ply do i just use adhesive should it be screwd down as well.

Does the decoupling mat go between the ply and cement board or the cement board and the tile?

Plumber wants to fix shower base directly onto the ply and has asked me not to fix cement backer board where the shower tray is going...is this correct?

you should also screw the cement boards down, every 150mm.
the decoupling mat will go on top of the cement boards.
the shower base will be okay on the ply provided the ply is fixed solid and that you don't have any height issues regarding the tiles being close to the top of the tray