Advice needed PLEASE.

25 Nov 2008
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United Kingdom

We finished building our house in December (we had individual contractors in for each trade, not one main contractor)

We are now having issues with the tiles on the ground floor, we have under floor heating and liquid screed (screed had been down for almost 4months before tiling). The tiles are all starting to come loose, it worse in the heavily used walking area so the kitchen is the worst affected. We also have 2 cracked tiles, 1 is by a door way and the other in a corner of the room. Both are very tight to the wall and door liner, not even enough room for a proper bit of grout 1mm max.

We supplied all the materials but my tiler told me where to get the materials from. He is blaming the UFH as we had issues with it, could this be true. About 2 weeks after the tiles had been down we switched on the UFH but it was not working, the electrician and Plummer were both blaming each other. They both were in working late one evening and got it working, when we came back the next day the house was boiling, the room stats were on 25deg. So the tiler is saying this has blown the tiles as it got too hot. Is what he is saying correct.

Any Advice is welcome
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What adhesive did you use and which primer did you use to prime the floor?

The liquid screeds are known as Anhydrite or Calcium Sulphate Screed..... Gypsum based. You therefore cannot tile directly onto it with cement based adhesive as a chemical reaction between them creates Ettringite crystals which will cause the adhesive to debond. (I guess the adhesive has stuck to the tiles and not the screed?)

If tiling on Anhydrite, you need to mechanically remove the laitance, hoover up the loose dust, prime with an acrylic primer such as BAL APD (2 coats) and then use a flexible cement based adhesive.

However there are adhesives on the market now such as Tilemaster Anhyfix, which you can use to directly to the anhydrite after the laitance has been removed, without the need for priming. This adhesive however is only suitable for dry areas.

With piped underfloor heating, it must be fully commissioned before any tiles are laid so that the screed can naturally adapt. if this doesn't happen, after tiling the screed could crack and any tile above it will follow. It is also recommended to lay a de-coupling membrane over newer screeds. Its not essential but may have prevented your issue from happening. It would cost less to lay that than the amount it would cost to replace the whole floor further down the line.

Underfloor heating too hot is a bit of a cop-out excuse unless its quartz tile that you have laid. Did the tiler tell you what to buy? He should have also laid with min 3mm grout joints (as per BS5385). If the total areas is more than 20-25 sqm, have expansion joints been used? has a perimeter joint been left?

I'm sure the screed type and the adhesive is the most likely causes, but there are other possibilities. As much info as you can provide about the products used, the better idea we'll have of where its all gone wrong. Also if you have any loose tiles, can one be lifted so the you can post a picture of the underside of the tile and the floor beneath?
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