Sorry Alan but I could do with your advise, I am currently preparing a 170m2 floor. The floor is sand and cement fiber screed, over hot water ufh with kingspan underneath, when I priced the job I told the customer the heating system should be commissioned before tiling. My question is as the screed was not closed in very well I put a skim screed of Mapei latex plan trade, before over-laying a de-coupling membrane. The day joints also had opened up, so I thought the slc might knit the floor in cracked areas.


I found out today that the floor has not been commissioned heat wise, just pressure tested. I would like your opinion as to if the floor could be heated up at this stage, before the tiling commences. Sorry to go on, but I was under the impression that the floor had been fired up before I started. Any imput would be very welcome

I would say that it is essential that they commission and run the heating before you put the tiles down. There is some risk that heating the screed up will cause it to crack as these screeds do. It will also determine whether any delamination of the smoothing compound is likely.

The SLC will not be capable of knitting hte cracked areas but as you have overlaid with an uncoupling membrane this gives you a fighting chance.

My advice is do not do any further work untill the heating is comissioned. then see what happens. If you need further advice at that point then holler.

Did you put anything in writing to cover your backside?

Thanks for that Alan, tiles wont arrive for another two weeks. Give them chance to fire it up, would you suggest bringing up the temp slowly as usual? the slc was two part with latex. Do you think this might help avoid any problems? Thanks again

Start the heating up at 20 degrees and leave it for 3 days. lift the temperature by a MAXIMUM of 5 degrees per day aftet that up to its maximum operating temperature but don't exceed 55 degrees C flow temperature. leave here for 3 days and then reduce by the same 5 degrees per day back to ambient and then either tile it whilst it is at ambient (if the weather is particularly cold this is useful) or switch it off. If you take the switch it off option don't start tiling for around 2 or 3 days because the screed will need to contract fully. It is the hot bit in the middle and this final contraction that will usually show up issues with the leveller but I supect as it is cement on cement there won't be any issues.

Cheers Alan, as I said I was under the impression this had been done, before I started. You have put my mind at rest. Thanks