Advice on floor prep prior to tiling please

[Aki Nawaz]

Hello everybody.

My first post on here; any advice and pointers greatly appreciated.


Ground floor extension c45m2.
Wet UFH system under 50mm of calcium screed (thermio plus).
Screed went down 4 weeks ago (sanded down after 2 weeks).
Final tile is a 600 x 300 porcelain.

I have had several tilers around and am getting conflicting views on how to approach this job. One tiler has said that ditra matting is a must between the screed and tile. While others have said not required. Also seem to be variation in the adhesive; some say a cementious one as ok; others not.

Any thoughts on the need for ditra matting, the type of adhesive and any other pointers are very much appreciated.

Thanks in advance.

 

[Glynn]

The tiling of these screeds is dictated by moisture levels in the screeds and this process cannot be short cut. Moisture readings MUST be taken with a suitable metre. We would always recommend the use of a gypsum based adhesive as you remove the chance of ettringite forming which will cause the tiles to fail. For a gypsum adhesive it needs to be below 85%RH (relative humidity).Cement based adhesive can be used but not till the screed is below 75%RH. Theses screeds will always fail if short cuts are taken. If you or any one else contact me at Tilemaster I will email you our full specification for preparing and tiling to an anhydrite screed. I will repeat myself "this process cannot be short cut". Ditra is always recommended onto under floor heating but with porcelain we do not insist on it if you are using a good quality gypsum adhesive.

 

[Aki Nawaz]

Thanks Glynn. I was aware of the moisture levels needing to be below a certain point. Thanks for reiterating and emphasising how critical they are to ensure the job is a good one. Have had a quick look on your website and have also sent you an email. Thanks again.