Hi, I hope you can give your advice on the following:

I have to prepare a floor ready for tiling. I have taken the 22mm chipboard up which was never screwed down. I am going to add noggins as there are not any at the moment and fix new 25mm plywood.

This is the ground floor of an extension (timber joists) which meets the old part of the house with a concrete floor. All the Karndean of this part has been stripped and the floor cleaned.

What is the best policy now please? Hardi over the ply? and then levelling compound over the screed to make level and flat? Uncoupling membrane over all of it?

Suggestions really appreciated!

Thanks Richard.

NMP over the 18mm ply will give you a superb tiling surface. You will also need to incorporate an expansion movement joint over where the two floors meet.

What tiles are you fixing?

Thanks for the quick reply! I think they are going to use some form of slate, however, they may change their mind , so want to allow for the worst!

So I can use 18mm rather than 25mm ? Does the no more ply need tile adhesive underneath the same way as Hardi? Also would I stop the NMP at the join in the floor and treat the 2 floors differently IE nmp on the wood and self levelling on the screed?

Thanks very much

R

18 mm plus 6mm nmp is fine if it gives you the correct height between the two different floors, nmp is usually glued and screwed although some fixers do use a flexible adhesive along with the correct screws and washers.
Dont carry anything over the joint between the floors except the expansion joint, you can either buy one in the correct colour or make your own using silicone to match the grout.

As you are fixing to two different surfaces then a de-coupling membrane would be a good idea.
If your customer decides on slate then be sure to remove the dust from the back before fixing.

Thanks, thats great advice.
r