Tiling on to concrete with water underfloor heating system

[outonthetiles]

I am tiling onto concrete screed laid 5 months ago. The underfloor heating is a water system which is soon to be turned on and tested. I will be laying 60x60 porcelain tiles over 100 sq mtrs. I have overdosed on technical info so much so my brain is scrambled. The adhesive manufactures all make similar claims for their flexible products whilst decoupling membrane manufactures claim their product to be essential for tiling over UFH and tile retailer want to sell me everything.

My questions are:

• Do I really need to use decoupling membrane if the screed is 5/6 month old? When the UFH is tested and turned on, I intend to keep it on low for a month or so to encourage the concrete to dry out even more than it all ready has before I tile.
• Due to the vast area being tiled, I will need to introduce expansion/movement joints. I have seen the preformed joints but I have also known tilers to do Silicon joints.

Your advice and views would be most welcome.

 

[afright]

I always use a uncoupling mat on all floors with wet ufh and movement joint profiles I stick with Schluter and never had a problem.

 

[Ajax123]

Uncoupling is not essential with porcelain as long as the substrate is sound and dry. It would do no harm and lots of tilers would still use it in this scenario.

Joints for for porcs on heated screed I think are maximum 8linear meters. Maximum bay size 40m2 The joints in the concrete should also be followed through your tiles. Joints through door thresholds as well.

if there are no joints in the concrete the whole thing changes. There should be joints in specific areas and if not present the screed is at risk of cracking and becoming un send. In that case uncoupling becomes much more necessary.

 

[outonthetiles]

Thanks guys, your views help me a lot. I have just spoken to Coppards who supplied the screed. They assured me it is top quality and with fibres. The screeders also commented on the quality, so I am happy with the screed. As the screed has had 5 months to dry out I think I will not be using the uncoupling membrane. I will put expansion joints at all thresholds and every 8mtr run. I will do solid bed tiling with 4mm spacing. Then keep my fingers crossed. My knees are aching already.