I am renovating an old house, and plan to fit underfloor heating mat in a bathroom. the area is about 2.5 m2 the existing concrete floor is in very good nick, but I need to raise it in order to accommodate the drainage from the shower and W/H basin. I will do this by laying thermalite insulation blocks on their flat surface, which will give 4" of rising, this will be OK for the drains to run. Should I be able to lay the mat directly on to the blocks,having ensured that they are level, r do I need to fix insulating board first and then lay the mat. ? I will then tile over the mat. I have plenty of room to work as there is a 6" step down into the bathroom. Any special tiles I need to use, and what about type of adhesive and grout?
Just a suggestion...don't use thermalite blocks, it's not the thing to do and will be a pain to get any kind of 'level' surface. You'd be much better putting some celotex down then screeding over the top. This will give you a better surface to work from and will work well regarding your drainage.
The blocks are already in place and are fixed down The surface is very smooth and level, there are no voids ,so as I said in the OP I am hoping to be able to lay the mat directly on to this. What I am unsure about is ..do I need to fix insulating board on to the blocks ,or can I just la the mat straight on to the blocks, or should I put a layer of skim adhesive down and then lay the mat. ? any advice welcome.
And thats what I have now done, it was very easy and gave a perfect surface to lay the mat&tiles. Now wait for 3 weeks to let the adhesive set then switch on!! hoping for nice warm feet. Thanks.