Hi all; I need help: I have an 8"concrete roof over a 12' X 30' cellar/basement which will become a walk on patio, on which I intend to lay a finish consisting of 2" natural stone slabs. The basement is fully tanked with stuck on 0.5" sarnafil membrane throughout (under floor, up walls, over roof). What do I use as a separating material between the sloped, tanked concrete roof and the 2 1/2" sand/cement screed, which I intend putting under the stone slabs, to allow for any movement between the screed and tanking without tearng/damaging the tanking? I am in Ireland by the way.:boxing: