Polished concrete overlay with DITRA anti-fracture membrane
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.
R&D
We figured it would work, and decided to do a little research and development in a friends 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, we were offered very little support from the self levelling providers and decided call from past experience and “wing it”.
THE PROCESS:
- 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 Finished Product
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.
