does wet UFH need ditra matting???

[adros88]

Hi. I have a sand and cement screed (75mm deep) with wet underfloor heating installed. The screed will be 5 weeks old when tiles are planned to go down. The underfloor heating will have been run up to temp and down over the 5th week. I'm currently getting quotes to tile it. I've read that a de-coupling mat should be used but as with most things in life everyone seems to have different opinions :lol: We have chosen a modular porcelin tile. The only thing that is agreed on is that the screed isn't a great level so they all want to latex it first. As the rest of the downstairs is being latexed due to a poor original screed it's no big deal to get the kitchen done at the same time.

Any advice on drying times and the use of a matting would be really helpful.

Many thanks

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[dave l and l]

i would go for the matting everytime

 

[paul flight]

you have two dif screeds one old and one new it is more than likley that the joint in between them will have movement due to settelment .also the floor will contract and exspand with the heating .so decouple it with matting afte levelling it with a flexibale latex ..hope and make sure yuo get a full width of matting where the floors meet.

 

[bugs183]

I'd go with an uncoupling membrane every time. I always talk the customer through the pro's and cons about them. Also i don't believe that a porcelain tile is any less likely to crack than stone, so i recommend a membrane for all floor tiles.
I prefer Ditra, can't explain why i just get a better 'vibe' about it over Dural.
Underfloor heated screeds can and do crack.

 

[adros88]

Thanks everyone for the advice. I've been using this site for a while and got loads of useful advice from other posts. I've had two tilers round to quote (did try for 3 but got stood up by the first two i booked to meet!) Neither of them mentioned matting until I brought it up. They didn't seem too bothered about putting it in but I think I'm going to insist on it.

The new screed only meets the old at the door way between the hallway and the new kitchen floor, so the ditra can start flush with the door.

Does the extra adhesive used to lay the matting make much difference to the UFH performance?

 

[Ajax123]

Uncoupling is not essential however in line with the other recomendations and for the sakeof the relatively small cost in comparison to the possibility of the screed cracking and causing a tile I also I think I would go for it on this type of screed.

I am concerned that ou think that you can run the heating up to temperature and down again ready for tiling in a single week. To do this properly and despite the advice given in the British standards which is very poor this runup and down should be gradual. Switch on at ambient and leave for three days, increase by max 5 degrees per day up to maximum temperature, leave at this for three days then reduce the temperature by the same maximum 5 degrees per day then switch it off for three days prior to moisture testing and finally tiling ifit is dry enough. Any quicker than this and you could well end up with crazy paving.

 

[bugs183]

The ditra and adhesive won't make any difference to the performance of the u/f/h Adros.

 

[Shamblehouse]

This is interesting.

Would you guys still recommend ditra if the screed was a liquid one like lafarge or truflo? with a bog standard ceramic tile?

 

[bugs183]

Yea i would, virtualy every screed i've seen of this type has crack in it somewhere.

 

[Dave H]

I would always use Ditra, if you use anhydrate liquid screed, be prepared for
much longer drying time, surface will need to be scarrified to remove top surface
and primed once fully dried out