Floor screed calculator

A bonded sand-cement screed needs at least 40 mm, a floating screed over insulation 50 mm, and 65 mm with underfloor heating pipes covered by 30+ mm. Self-leveling compound works from 3–5 mm over a sound, primed substrate.

A 1:3 mix takes roughly 450 kg of cement and 1.35 t of sharp sand per cubic metre — about 22 kg of cement and 68 kg of sand per m² at 50 mm. Semi-dry consistency (a squeezed handful holds shape without dripping) gives the strongest screed.

Floating screeds over insulation and any screed with underfloor heating should carry mesh or polypropylene fiber (about 0.9 kg/m³) to control cracking. A bonded screed on primed concrete usually manages without.

Foot traffic after 24–48 hours, but full drying runs about 1 day per mm up to 40 mm and slower beyond — a 50 mm screed needs 6–8 weeks before moisture-sensitive flooring. Force-drying too early causes curling and cracks.