My folks have just had a proper roof put on the conservatory that my dad built 30 years ago. They were toying with the idea of new tiles and UFH. They've seen Trav they like hence the decoupling system. I knew my dad would never commit so I went round after work with an SDS and said I'll have all the quarries he fixed when I was a kid up in an hour. 3 hours later - not even 1/2 way. My dad couldn't remember (he used a Wickes 'how to' guide to tiling) but he must have laid a 2nd screed over the original slab and then tiled. Quarries are coming off in bloody layers and although the 2nd screed came up really well where I started,
it's now as bad as the tiles.
Good thing though is the slab is in great condition and when it's all up there will be plenty of room for 20mm insulation boards.