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

 

[tpt]

sorry to say you have been given bad advice. The new 'waterproof' chip that is used in building now is coated and hardly anything sticks to it. s2 adhesives will stand the flexing but your tiles wont and its a recipe for failures.

I'd suggest you have 2 options:
1. rip up and lay 25mm WBP ply instead of the chipboard
2. overboard the chip with no more ply - this is stuck down and screwed but your builder is right, you may not have enough anchor points.

Either option will be influenced by the span, size and width between the joists. modern upper floors can have a lot of bounce in them. plus your UFH will add thermal movement too!

Best thing really is to speak to a well known adhesive manufacturer such as bal or granfix - both have a technical help line but you'll get asked some technical questions so may be worth having your builder on hand.

The join between the rooms is a different issue though, it probably just needs a joint that allows movement as the two rooms will always move at different rates

 

[Richard C]

Ditto from me. Cut your losses now while you can, you will just be throwing good money after bad. Rip up & dump the chip its total crap & probably the worst possible tile base you could possibly have. Use 18-25mm WBP ply, actual thickness you need will depend on your joist size/pitch/span.

The new floor must be level, flat & have no discernable flex if your tiles are to last. Also if you have two different floors meeting you may need an uncoupling membrane or, again, the tiles may fail due to differential movement between the two floor areas.

 

[heellllppp]

Hi and thanks for your comments. The problem we have got is that the kitchen is sat on top of the chipboard and ripping this out would mean taking the kitchen out too. I am thinking that maybe we should take the tiles up and put laminate flooring down but I am not sure this would work either with the floor not being level. I am grateful for any suggestions.

Thanks

Sarah

 

[JohnD]

Chipboard is an ideal material for putting on










a bonfire