Hi there to all you pro tilers, please can I have some advice, I have an area of 60m in total to tile. I have put down under floor heating (water)and then approx 60mm thick of liquid self leveling screed which has been down about 8 weeks. The underfloor heating has been on for 2 weeks and the floor looks dry. How can I be sure the floor is fully dry, what floor sealant/primer should be used. Does the underfloor heating have to be on or off when tiling any advice will be appreciated
Regards Jonnie p

Have a read of this Anhydrite screed

Heating needs to be off and floor back to normal temp. drying time is 1mm per day. but having the heat on would have helped it along.

after 8 weeks , plus the heating being on it should be fine by now.make sure heating is off before tiling and floor is at normal temp, other wise addy will set to quick,
CREATIVE IMPRESSIONS to adhesives for gyvlon floors and primers just google it

Firstly , what type of screed is it. ?

Hi there thanks for all the advice, the sceed is alpha hemi hydrate self leveling screed. The screeding company are advising me to put down an aycrilic primer bonding agent does this sound correct.
Regards Jon

sounds fully dry to me, we normally quote 6 weeks. you could always prime it with unibond 6-1 water, to be sure but not really worth it, but you must use a flexible 1 part mix adhesive and matching grout, youll need about 13-14 bags at 20kg, and if you pay more than XX pounds a bag youre being ripped off, DONT use Topps Tiles. Hope thats of help

I think that the OP should read some of the earlier threads on this type of screed (Calcium Sulphate) and take note of the correct method of priming and preparing the surface prior to tiling.
Unless tilers have an in depth knowledge of this product, to advise/suggest/comment without experience could mislead.

As TJ for me, I was under the impession Unibond was PVA.

Same as, unibond is a pva..

Originally Posted by Bristol Tilers

sounds fully dry to me, we normally quote 6 weeks. you could always prime it with unibond 6-1 water, to be sure but not really worth it, but you must use a flexible 1 part mix adhesive and matching grout, youll need about 13-14 bags at 20kg, and if you pay more than XX pounds a bag youre being ripped off, DONT use Topps Tiles. Hope thats of help

Aaaaaaaaarrrrrgggghhhhhh!!!!!!!!!!

Creative Impressions or Nicobond adhesives specifically for gypsum based screeds. Alpha Hemi Hydrate is one of the three types of gypsum based screeds. Prep and priming is the same for them all. Lightly sand to remove any loose debris on top, vaccuum up any dust, prime if necessary with an appropriate acrylic primer (the two above adhesive manufacturers will give guidance on primers) then tile.

drying rate is 1mm per day for the first 40mm depth and then add 2 days per mm for each mm over 40mm i.e. 50mm screed takes 60 days based on good drying conditions. we have had very poor drying conditions for the last 8 weeks or so. The heating will help but it is dependent on temperatures and humidities. The only way to be sure is to test it with a hygrometer. (requires investment of approx £80)

Thanks Ajax123,
I managed to borrow a Tramex cmex meter which gave back readings of 2 for moisture content of the floor which I have been told is ok to tile on. The floor is heated at night with a industial de humidifer going and during the day fully ventilated with doors and windows open which gives a steady breeze over the screed this seems to be working very well, not sure if this the correct method.
I am thinking of using Mapei Primer G ?

You can leave the UFH on when installing the system, you want to avoid ever turning a warm water UFH system completely off. A good sealer/primer to use is BAL bond SBR but any standard primer to seal down dust and create a tacky surface once you have hoovered of course.

dehumidifier - close the windows......
no dehumidifier open the windows.......

the primer becomes largely irrelevent if you choose a gypsum based tile adhesive but if you have decided on cement the primer is the most critical part. Primer G i beleive needs to be diluted for the first coat 1:1 with water and the second coat neat. Make sure you get a written method from the manufacturer and follow it to the letter.

When asked Mapei recently they recommended Eco Prim T.

You are right they moved away from primer g a while ago in favour of ecoprim t. It still needs diluting first coat though.

Thanks to everyone for all the advice