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How to tile on top of suspended floor joists.
Knocked down wall between kitchen and dining room to create large kitchen/diner, approx 36 square metres. Removed old floor boards and replaced joists with 125x47mm joists (couldn't be any bigger because of height restrictions). Now want to tile entire area with natural stone (probably 400x600mm tile size), but have had conflicting advice from tradesmen, one to screw 18mm plywood to joists and then tile on top, another to use tilebacker boards (6mm) screwed to joists and tile directly unto those (would help with height restriction, but don't want to have to much movement or fall through floor), so any solutions would be welcome.
Hi there is a lot of weight going on the floor so you need to make it deflection free (bounce)
I can only comment on what I would do as not knowing on the floor joist ,18mm ply(wbp)then prime with SBR ,using flex floor adhesive glue then screw 6mm backer board if possible 12mm to ply,6mm backer board will not do on its own if you have height restriction then I suggest you change the tiles Natural stone need a good sold base any deflection in the floor they would be prone to cracking.Further more to comments made by D B Enterprise which are correct the matting can be used but is only for lateral movement not deflection thats why you would use backer board to compensate this if using the matting it is called Schluter ditra.
Answered 10th Apr 2013
There is a lot of discussion about tiling on timber floors and I have found that most information is very poor.
In your case the joists seem undersized for the span especially given the weight that you are about to load onto them.This is definitely worth checking
If you must tile a timber floor and the joists are sound then I have found that the best solution is as follows.
The main problem is deflection (bounce) and thermal movement (expansion and contraction)
Most flexible adhesives on their do not allow for the type of movement found in a timber floor especially over a large area.
The best way to overcome the problem as long as the floor is relatively sound is to a screw and glue 18-25mm ply to the floor. The screws are to be fixed 150mm apart. This is done purely to stiffen the floor as best as possible.
Onto the ply, a product call ''Dertimat' is fitted. This is an expansion material and will allow far more movement than adhesive alone. Then onto this you adhere your tiles.
We have never had a floor fail using this method but you must make sure that the joists are suitable for the span of the room
Answered 12th Apr 2013