I want to install an in-floor water based heating system in an apartment on a higher floor.

As such, there are 2 problems:

  1. I cannot afford to have 2 layers of screed (because I need something lighter).

  2. The current concrete slab suffers from level and adherence issues. There are holes, level differences between rooms of up to 6 cm, 2 rooms have a layer of bitum on them (was previously used as insulation and adhesive for the former flooring), 1 room has a slab of shiny mosaic-like screed that we couldn't remove.

This is why I thought about using perlite as the bottom layer (under the studded insulation panels).


  1. Is this a good solution?
  2. Does the studded insulation panel need to be anchored to the surface below using screws or something else?
  3. Will it have enough stability on the perlite layer if I level it appropriately?
  • perlite can be crushed in your fingers, so i don't think it would hold up very long on the floor. you can mix it with concrete though. – dandavis Aug 10 '18 at 20:35
  • I am referring to dry granulated perlite that looks like sand. Do you think that the granules will become smaller and smaller when they are under insulation panels (which are covered by 4-5 cm of concrete screed)? – ROMANIA_engineer Aug 10 '18 at 20:42
  • that was my fear. my experience with perlite was more agricultural, but the bags of that stuff do make a very fine dust, and i've "smooshed" one of the pea-sized particles down to powder in my fingers. maybe your perlite is different, but i would go with other materials; it's not like you need perlite's water-wicking... – dandavis Aug 10 '18 at 20:46

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