Levelling compound for underfloor heating – calcium sulphate, fibre-reinforced, 25 kg bag

Consumption is approx. 1.4 kg/m² per mm of thickness. In the NerthusFlow low-profile system the layer thickness depends on the membrane: 13 mm for 10/12 mm pipe, 15 mm for 14 mm and 17 mm for 16 mm – each plus 5–6 mm of pipe cover.

This gives approx. 25–27 kg/m² (10/12 mm), 28–29 kg/m² (14 mm) or 31–32 kg/m² (16 mm) – i.e. around 1 to 1.3 bags per m². Example: 25 m² with 16 mm pipe = approx. 770 kg, which is 31 bags.

Order a few more bags than calculated – we recommend a 5–10 % reserve for unevenness, edge areas and leftovers. An area must be poured in one go.

The surface is walkable after approx. 3 hours (depending on temperature). Readiness for covering depends on thickness and covering: at 5 mm after approx. 24 h for textile, resilient, ceramic and natural stone coverings and after approx. 36 h for parquet; at 10 mm after approx. 48 and 72 h respectively.

Guide values at 20 °C and 65 % relative humidity.

Yes. Suitable substrates are gypsum and anhydrite, magnesite floors, mastic asphalt, floorboards, dry screed elements and chipboard – the fibre reinforcement keeps the compound low-crack even on moving timber substrates.

Per DIN 18365 the substrate must be firm, load-bearing, clean and permanently dry. Remove friable areas and then prime with a primer suited to the substrate. For dry indoor areas only.

Yes. Remove friable areas, then prime the substrate with a suitable primer matched to it. Absorbent substrates such as anhydrite or floorboards must be primed so that the compound flows evenly and does not lose water too quickly.

Up to 20 mm is possible in one pass. For thicker layers the mortar can be extended with dried quartz sand by a maximum of 30 %; reduce the amount of water accordingly.