Tiling on top of wet under floor heating

[heellllppp]

We have just built a first floor extension on to the side of the house which is attached to our existing kitchen. We had laid wet under floor heating in between the joist and covered this with 22mm kaber chipboard which was screwed down in lots of places (apologies for lack of techinical knowledge)

Our builder asked our local national tile shop for advise on laying tiles on top and they suggested that it would be fine as long as we used to 2 part flexi adhesive and flexi grout which we did.

Within days, several tiles started to rock, just on the corners and the grout was becoming dislodged. These tiles are on the new and old floor After taking up a tile, the adhesive was stuck to both the tile and the chipboard. Puzzled, we asked around and people have suggested that we should have left the UFH off for at least a week.

We turned the UFH off, took up the rocking tiles and replaced them. We have now discovered the whole row of tiles where new room meets old are rocking. We have put a spirit level over the area and they are out by 10mm.
Any suggestions would be appreciated as it has already cost a fortune as the room is 32m2.
The builder said he can't put 6mm ply over the chipboard as it would have to be screwed down more often than just in the joist which could puncture the underfloor heating.

Thanks

Sarah

[Colour Republic]

6mm ply is too thin anyway, the moisture from the adhesive would make it warp,

Heating should have been left of for 4 weeks then brought up to temp slowly (increase by 1 degree per day) you could have a few issues, too much deflection in the floor, how was the adhesive applied?? Was it combed or put down in dabs?, the floor could also need to be primed depending on addy used.

Any pictures?

[heellllppp]

Thanks for your response. The floor was primed and the adhesive was smeared not dabbed. It is hard to show on a picture as all the tiles are still down at the moment. When the builder took the tiles up to replace them they were really stuck down, even the corners that were rocking had adhesive on the tile and floor which makes me think it has been stuck down fully at some point. Do you think it could be movement in the chipboard. Any suggestions on how to solve it as we can't go on for ever taking rocking tiles up and replacing them.

Thanks

Sarah

[Colour Republic]

The 'National Local Tile Shop' was it Topps by any chance? Sometimes the staff aren't qualified to make judgements to be honest with you.

You say the tiles have lifted mainly where old meets new. It would have been best practice to have an expansion joint here as the two floors may be expanding and contracting at different rates.

Your issue does sound like deflection (i.e. too much bounce in the floor) but it really is hard to call without seeing it.

There are products which can help you but any major problem with the floor would have to be rectified first and sometimes that can mean the whole floor coming up. 6mm ply is not going to help. You could use 6mm tile backer boards (the excuse about puncturing the UFH is bending the truth 22mm chipboard + 6 mm tile backer board = 28mm so any screws smaller than this would not puncture anything! in addition the boards could be glued and screwed) A decoupling membrane could also be used...

What tiles are they? Porcs or a natural stone?

In all honesty the addy could have been shocked by the UFH and may need to be removed anyway.

I know it's not what you want to hear. Sorry

I would ask some independent tilers to come round and give their views. Keep in mind some tilers aren't always at the top of their game like most trades so I would give them the problem and not offer too much info on what you've been told and listen to the ones who go into the most technical detail. One of the first questions they should ask you is "How long after the tiles were installed was the UFH commissioned"

[tictic]

Thermal shock...this has what has caused it,it all going to fail...sorry get your "builder " back ....he done the job,and didn't have a bloody clue what he was doing!!!....he has to redo at his cost..not yours...

And tell him to get a tile fixer that knows what he is doing..ie how he is going to do the job...step by step...


Never ever get a builder to do tile fixing....they ain't got a clue.

[tictic]

Tell your builder or tile fixer to look into brio boards for your wet ufh...
They only sell this by the pallet tho ,depends on your area off m2 .