Limecrete floor with UFH - decoupling membrane?

[FCC]

Hello

After people's experiences of limecrete floor with UFH and laying of tiles. We are getting ready to lay limestone tiles (15mm thick) over our limecrete floor which has UFH. Planning on bedding these down with a lime mortar mix as have lime left over from laying the floor. Brief googling gives mixed results re whether to use a decoupling membrane or not but it does seem that lime products won't stick to a membrane and obviously the majority of membranes aren't breathable (although neither will the limestone tiles after they have been sealed!)

Anyone out there had experience of the above and have you had any issues with the lack of a decoupling membrane?

Thanks in advance

 

[Kearn]

Remember your limecrete slab is also not breathable. Nothing here is managing moisture if you have RFG as your sub layer.

The membrane is break for movement, so you need to really evaluate how much you think cracking and possible expansion may occur from heating your slab and whether this could transfer through to the tiles - either lifting them to break their adhesion or cracking them. Limestone is fragile in that plane, and 15mm is quite thin.

I’ve done both, bedded directly with a thick lime bedding layer 40-80mm without a membrane, as my slab was thick and the pipes were a long way down… on a couple of floors, with 22mm limestone slabs. I’ve a few slabs which have slightly broken their adhesion, sound a touch hollow - this could be due to no membrane, it could also be other things. The slabs I used had a very smooth machined rear, so no key, just suction to rely on. I used a couple of different gritty adhesives (different floors) on the rear of the tiles to help with key.
I’ve also recently used a membrane with the same tiles, but over a thin 50-70mm poured concrete flow screed containing the UFH pipes and with only 10mm bedding depth to play with, so more chance of movement.

The reality of the membrane in my setup made little difference - a bit more time to lay it and let the adhesive go off, but the cost of the membrane balanced out the cost saved in less tile adhesive required as the mat was 3mm thick, so a third less adhesive in my setup.

The lack of lime adhering to the membrane, may actually create more issues.