gc100 Posted September 28, 2020 Share Posted September 28, 2020 Hi, My anhydrite based flow screed has been down for since 22 of May and is about 50mm so should be fully dry now (its also had a constant breeze flowing). Due to various schedules I cannot get the UFH commissioned until towards the end of Oct and we want to start putting tiles down well before. Reading online its seems its alway recommended to do a round of heating (and cooling) of the floor before installing however given my timelines this isn't really possible. I'm now planning to use Ditra decoupling matting to held alleviate any heating cracks. Has anyone done this or am I just asking for a lot of trouble? Link to comment Share on other sites More sharing options...
Nickfromwales Posted September 28, 2020 Share Posted September 28, 2020 Doing that cycle is referred to as a “thermal shock” of the slab. I wouldn’t be worried about that. The fact it’s Anhydrite is the worry. Has it been mechanically abraded after curing? There will be a scum layer that will stop anything sticking to the screed that needs to be dealt with, as nothing, and I mean nothing, will stick to it. Ditra, tile adhesive, primer, nowt. I’ve been on jobs where 80+m2 of floor tiles are able to be lifted up with just the grout holding them together. Ask questions, get answers Link to comment Share on other sites More sharing options...
gc100 Posted September 28, 2020 Author Share Posted September 28, 2020 Just now, Nickfromwales said: Doing that cycle is referred to as a “thermal shock” of the slab. I wouldn’t be worried about that. The fact it’s Anhydrite is the worry. Has it been mechanically abraded after curing? There will be a scum layer that will stop anything sticking to the screed that needs to be dealt with, as nothing, and I mean nothing, will stick to it. Ditra, tile adhesive, primer, nowt. I’ve been on jobs where 80+m2 of floor tiles are able to be lifted up with just the grout holding them together. Ask questions, get answers Hi Nick, Yes we mechanically abraded it all . Is the purpose of the thermal shock it make any would-be-cracks appear? Or is it something else? Link to comment Share on other sites More sharing options...
CC45 Posted September 28, 2020 Share Posted September 28, 2020 I didnt take a chance with ours - it had a good heat shock to get all the movement out of the way. 1 wee crack appeared in the slab which the tiler bridged over with some sort of membrane. If your tiler says to do it then I would - will he guarantee the job incl materials if it goes wrong? Link to comment Share on other sites More sharing options...
gc100 Posted September 28, 2020 Author Share Posted September 28, 2020 6 minutes ago, CC45 said: I didnt take a chance with ours - it had a good heat shock to get all the movement out of the way. 1 wee crack appeared in the slab which the tiler bridged over with some sort of membrane. If your tiler says to do it then I would - will he guarantee the job incl materials if it goes wrong? The builder is doing it, and no he doesn't guarantee (i'm paying day rate). Link to comment Share on other sites More sharing options...
Nickfromwales Posted September 28, 2020 Share Posted September 28, 2020 Just now, gc100 said: The builder is doing it, and no he doesn't guarantee (i'm paying day rate). Your builder is tiling? 48 minutes ago, gc100 said: Yes we mechanically abraded it all . Good stuff. Just switch the heating on for 48 hours and run it at around 30oC. What will be will be. ? Link to comment Share on other sites More sharing options...
CC45 Posted September 28, 2020 Share Posted September 28, 2020 Its a risk - not sure I could face the problem if it did rear its head... Link to comment Share on other sites More sharing options...
nod Posted September 28, 2020 Share Posted September 28, 2020 1 hour ago, gc100 said: Hi, My anhydrite based flow screed has been down for since 22 of May and is about 50mm so should be fully dry now (its also had a constant breeze flowing). Due to various schedules I cannot get the UFH commissioned until towards the end of Oct and we want to start putting tiles down well before. Reading online its seems its alway recommended to do a round of heating (and cooling) of the floor before installing however given my timelines this isn't really possible. I'm now planning to use Ditra decoupling matting to held alleviate any heating cracks. Has anyone done this or am I just asking for a lot of trouble? I would always run the heating before tiling As a business I’ve tiled plenty Usually commercial that simply can’t be heated up before tiling I did a favor job for The MD of a company that gives us lots of work Bio boiler wasn’t commissioned S&C screed had been down two weeks 200m2 needed to be down and grouted in two days No time to F##k about with Ditra His words 1200 Porcelain slats Four years on still fine He just said if it has to come up after Christmas So be it But I have to be in for Christmas Make sure you Leave a 10 mil gap around the edge and plenty of expansion joints and you will be ok Link to comment Share on other sites More sharing options...
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