Question: Can polished concrete overlay's be applied over wood substates , with Schluter 's DITRA HEAT anti fracture membrane?
Try to get a straight answer from any of the big self levelling manufacturing companies including: Rapid Set, Mapei, and Ardex, or from Schluter themselves - it won't happen!
I figured it would work, and decided to do a little research and development in my 100 year old house. It was the perfect worst case scenario. The floor was 2" out of level over 10 ft, the space was a 4th floor attic and access was a spiral staircase. After many calls and research, I was offered very little support from the self levelling providers and decided call from past experience and "wing it"
- LEVELING - Levelled out the low spots with a high polymer patching material. This took several steps as some materials feather to 1/2" and others to 1/16". I tired to get the floor as smooth and flat as possible, mortared the Ditra anti fracture membrane to the floor as per instructions.
- NUHEAT INSTALLATION - Simply snap the heating cable into the receivers in the areas you want the heat.
- SCRATCH COAT - This is where the "make it up as you go" begins. Applied a scratch coat at 1/8", over top of the DITRA membrane. The scratch coat was a high quality self levelling overlay material. Broadcast coarse sand into the scratch coat until rejection, and vacuumed up the excess. Primed the scratch coat once dry.
- SELF LEVEL - Applied the 1/4" self leveling overlay
- POLISH - polished the 1/4" overlay to 800 grit with concrete countertop polishing unit to minimize the weight on the floor.
The results are pretty impressive. In the centre of the room there is a massive 200kg free standing tub that holds two people and 327 Litres of water. I have seen a couple minuscule hair line cracks that after 6 months have not become any sort of an issue. This is definitely a possible application, cost on the other hand might make it prohibitive. As a guess it would run $15- $25 per sq/ft with the DITRA and nuheat system.