Short answer: as a rule of thumb, a screed dries at about one day per millimetre for the first 40 mm in good conditions (around 20°C with steady ventilation). Beyond 40 mm, drying slows sharply, often to two days per extra millimetre or more. A typical 65 mm floating sand and cement screed can therefore take two to three months to dry naturally.
Drying is not the same as curing
Curing is the early chemical hardening of the screed; drying is the slow loss of excess water afterwards. A screed may be hard enough to walk on in a day or two, yet still far too wet for most floor coverings.
Typical drying times
| Screed | Typical depth | Light foot traffic | Natural drying (guide) |
|---|---|---|---|
| Sand and cement, floating | 65–75 mm | 24–48 hours | Roughly 2–3 months |
| Sand and cement, bonded | 25–40 mm | 24–48 hours | Roughly 4–6 weeks |
| Liquid calcium sulphate | 35–50 mm | 24–48 hours | Roughly 5–8 weeks, faster with UFH force-drying |
| Fast-drying systems | Varies | Hours to 1 day | Days to 2 weeks, product-dependent |
These are planning figures only. The product data sheet and a moisture test always decide.
What slows drying down
- Cold, damp weather and buildings that are not yet weathertight
- Poor ventilation, or wet trades such as plastering in the same space
- Greater depth: thickness has a disproportionate effect
- Laitance left on the surface of liquid screeds
Using underfloor heating to speed things up
Many liquid screeds can be force-dried with the underfloor heating after about seven days; sand and cement screeds commonly need around 21 days first. Heat must be introduced gradually in steps, never at full temperature.
How to know it is dry enough
Use a hygrometer test, not guesswork. Many floor coverings require the screed to reach 75% relative humidity or lower, and timber floors often need drier. Your floor fitter and the covering manufacturer will confirm the limit.
A worked example
Take a 65 mm floating sand and cement screed in a new extension. The first 40 mm takes roughly 40 days in good conditions. The remaining 25 mm dries more slowly, at around two days per millimetre, adding about 50 days. That is roughly 90 days before many floor coverings can go down, which is why fast-drying screeds and liquid screeds over underfloor heating are so popular on tight programmes.
Do not try to rush it with heaters
Blasting a new screed with heaters or opening every window on a hot day dries the surface faster than the body of the screed. That uneven drying is a common cause of curling at the edges and surface cracking. Steady, moderate ventilation after the first couple of days is better than aggressive heat.
Quick answers
Can I walk on new screed? Usually after 24 to 48 hours for light foot traffic.
Can I put a dehumidifier in the room? Yes, once the screed has had its initial curing period. A dehumidifier in a closed room is one of the gentler ways to help drying.
Does a thinner screed dry faster? Yes, much faster, but it must still meet the minimum depth for the build-up. See our screed thickness guide.
Need a floor ready by a set date? Ask us about fast-drying screed.
Written by Ben Phillips, director of Chelmsford Floor Screeding Ltd, floor screeding contractors based in Billericay with 20+ years of experience across Essex and London. More about us.