Floor tiles and Devimats

18 months ago we refurbished our first floor bathroom and had a Devimat installed under the floor tiles. Within six months the grout began to loosen and crack and recently a number of the floor tiles have begun to crack and the grout is looser than ever, even though the Devimat has hardly been on since Spring.
In 20-20 hindsight it seems obvious that as the tiles expand and contract in reaction to the Devimat's heat, the grout would suffer but I imagined this would somehow be allowed for... Anyone been through this or know something that should have been done that hasn't?

I think I may have the same problem although thankfully the tiles have not cracked but the grout is coming loose so I'm interested also.

mf

I enquired about getting those mats a few years back but for various reasons decided against them. If I remember correctly, I think we were advised to use a special grout. Sorry but I can't remember the exact details.

good to know...I'm getting them in this week

I'm ssuming that the first floor bathroom OP mentioned is on wooden floors. Tiles over devi on wooden floor might not be best with the natural expansion/contraction of the wood, hence cracks. Altho we have devi in ensuite, under tiles over wood and no cracks and done a few years. Its used all through winter too. I did remember the tiler saying something about the grout being more elasticised or somethig like that, maybe why not cracked.

Devi is very handy tho. Have it under tiles over contrete on ground floor in sunroom & office and is great.

AFAIK you need to use a flexible grout i.e. with special polymers added to allow the joints to cope with the minute movement expected when the tiles heat and cool. I'm sure a good tile shop can advise further. I'd imagine it would be important to use a fine (narrow) grout joint also (2- 3mm wide) to minimise the amount of movement.

Carpenter said:

AFAIK you need to use a flexible grout i.e. with special polymers added to allow the joints to cope with the minute movement expected when the tiles heat and cool. I'm sure a good tile shop can advise further. I'd imagine it would be important to use a fine (narrow) grout joint also (2- 3mm wide) to minimise the amount of movement.

Click to expand...

Thanks for the responses. Believe they were laid without flexible grout which (on looking into grouts) I see is recommended both for floating floors and underfloor heating. Will live and learn and have to pay yet again for careless work to be re-done. (Not sure the builder learnt anything though).

Some tips for laying the Devimat:

· If installing on a wooden floor make sure its marine plywood, at least 15mm thick, screwed to the joist every 6 inches.
· Make sure to use a flexible tile adhesive at all times with underfloor heating and tiles. (even on a concrete floor)
· If using a levelling compound over the Devimat, make sure its latex based.
· Dont cut the heating element (Devi does repair kits in case of an accident but dont cut it on purpose).
· Dont forget the floor sensor.

Cant think of any other tips right now. Mail me if you have a question.

Devi said:

Some tips for laying the Devimat:

· Make sure to use a flexible tile adhesive at all times with underfloor heating and tiles. (even on a concrete floor)

Click to expand...

And grout, sorry.