Advice - loose tiles over underfloor heating

23 Jan 2016
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United Kingdom
Hi. Would be grateful for some advice.

Our bathroom was fitted about 7 years ago, with porcelain (I think) tiles over electric underfloor heating. I don't recall what adhesive was used at this point, but we would have at least selected one suitable for use with underfloor heating, in a bathroom. It's sitting on a concrete floor with (I think) a layer of insulation on top. Builder did all the work and I didn't get involved in the spec beyond the tiles and the colour of the grout.

For the last few years there's been a problem with the grout between the tiles cracking and coming loose. I've finally got round to having a look at it, to find that all of the tiles appear to be loose (small but noticeable vertical movement) to some degree and some appear completely loose I've lifted a couple of them and found that they have separated cleanly from the adhesive underneath, so can be prised quite easily off the floor with no adhesive sticking to the tile. The adhesive is very crumbly in places, but quite solid in othersand is stuck pretty firmly to the floor beneath.

A further complication is that the adhesive seems to have been applied directly onto the underfloor heating wiring matrix - which doesn't sound like the right way to do it - so I can't really remove the old adhesive and would have to stick back on top of it.

A couple of hopeful questions:
Any 'thin' adhesive products out there? Something like a contact adhesive would allow me to stick down only the worst tiles as a temporary fix.
Any products you can squirt under a loose tile to fix it?

More realistically, my options are probably:
a) Lift everything, hopefully without damaging the underfloor heating, level off over the old adhesive and start again myself. Problem is that this will raise the floor level, and that's going to cause aggro with other fixtures and fittings.
b) Rip out what's there and get an underfloor heating professional to replace the lot.

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I'm been told by someone who does these things to use a flexible mastic to squirt under the tiles as best we can to hold them down. Sounds ropey, but I suppose it might work and doesn't really make things any worse if it fails....
Tiles expand a bit as they warm up. Then shrink when they cool down. Hence the adhesive has to be flexible to accomdate this movement. Or if laid using non flexibe adhesive then the floor has to be kept at roughly the same temperature all the time 24 hours a day 7 days a week.

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