My bathroom tiles, fitted by a contractor, are crackingexactly along the joins in the plywood boarding underneath.

The ceramic tiles were laid on 6mm ply on top of tongue and groove floorboards using (I'm told) flexible adhesive. The ply was laid with the long side running front to back in line with the boards underneath (not 90 degrees)

The contractor is trying to tell me that the reasons for the cracks is because there's movement in the joists. The joists have been laid for 70 years, a surveyor has looked and sees no sign of movement or rotting and so I could do with some advice on what could be the cause of the cracks.

In my mind, they should have used minimum 12mm of ply and laid it at 90 degrees to minimise the natural flex in the floor.

Does anyone else have experience of this?

Sorry I've got no experience of tiles cracking but your situation is the result of inadequate floor preparation!
British Standard guidelines are a minimum overlay for plywood is 15mm for ceramic tiles to be fixed!
Even if there is movement in the joists it is the contractors liability to make sure the floor is deflection free prior to receiving a tiled floor covering.
No doubt the start of a dispute!

12mm ply screwed every 6inch .flex adhesive+flex grout, jim the tiler.

Originally Posted by timeless john

Sorry I've got no experience of tiles cracking but your situation is the result of inadequate floor preparation!
British Standard guidelines are a minimum overlay for plywood is 15mm for ceramic tiles to be fixed!
Even if there is movement in the joists it is the contractors liability to make sure the floor is deflection free prior to receiving a tiled floor covering.
No doubt the start of a dispute!

You will need no other answer other than this one!

as tj has so rightly said

your contractor is right in his assertion that theres movement in the joists, hes wrong when he declines responsibilty for it as the deflection should have been dealt with prior to laying the new floor

your surveyor should know better and is ignoring the evidence in front of him, start by employing a decent surveyor who knows what hes looking at and get his support to get your tiler back to rectify the works

the suitability of the substrate for tiling is the tilers responsibility

I'm not so sure the surveyor has seen the tiling job, I'm guessing the survey was done at the time of purchasing the property mike

Originally Posted by Colour Republic

I'm not so sure the surveyor has seen the tiling job, I'm guessing the survey was done at the time of purchasing the property mike

well thats just a check to see that the property is sound and has nothing to do with this tiling job

as has been said by timeless john above , even if there was movement in the joists it is the tilers job to check if theres any movement in the floor before and after boarding and it is 100% his responsibility to do this before he tiles in my opinion, i personally wouldnt use anything less than 15mm ply on good solid floorboards, hope you get a result with your tiler as it is his fault.

Great feedback and as I thought...I questioned him on the 6mm ply and he said youcould use anything from 6-12mm and it was fine....I begged to differ. I think we may be at the start of a dispute as he is clearly baulking at the propsect of ripping up and starting again.

What about the boards being run in line with the floor boards and not at 90 degrees, is this another issue?

Surveyor has not assessed the tiling job, simply has identified that there is no failing of the joists or signs of rot.

Originally Posted by mikethetile

well thats just a check to see that the property is sound and has nothing to do with this tiling job

I don't disagree mike but from a home owners point of view you have a Tiler saying the joists are at fault and they have a surveyor saying they are sound so you see why they would come to the conclusion that the joist are ok, as you know being sound and deflection free are two very different things. In any case I don't think the joists are at fault but the tiler

Is he going to start over? I doubt it very much.
He needs to learn the job properly before taking on these jobs.

Originally Posted by Unregistered

Great feedback and as I thought...I questioned him on the 6mm ply and he said youcould use anything from 6-12mm and it was fine....I begged to differ. I think we may be at the start of a dispute as he is clearly baulking at the propsect of ripping up and starting again.

What about the boards being run in line with the floor boards and not at 90 degrees, is this another issue?

Surveyor has not assessed the tiling job, simply has identified that there is no failing of the joists or signs of rot.

Yes they should have been layed at 90degrees.