Screed Drying TimesAnd Aftercare That Protects The Floor
When you can walk on it, when trades can work on it, how to force dry safely through underfloor heating, and how to prove the floor is dry before a covering goes down.
How Long Does Liquid Screed Take To Dry?
There are two different questions hiding in that one. Curing is the chemical set: the screed gains strength within days. Drying is moisture leaving the slab, and that is what governs when tiles, vinyl, engineered timber or resin can go down.
For calcium sulphate flowing screed, the working rule in normal indoor conditions is roughly 1mm per day for the first 40mm, then noticeably slower beyond that. A 50mm floor therefore commonly needs around 50 to 60 days to reach a covering-ready moisture level if it is left to dry naturally. A proper commissioning cycle through the underfloor heating shortens that a great deal, which is why most well-run sites force dry rather than wait.
| Screed depth | Natural drying, indicative | With force drying |
|---|---|---|
| 40mm | Around 40 days | Substantially quicker once commissioning starts |
| 50mm | Around 50 to 60 days | Substantially quicker once commissioning starts |
| 65mm | 75 days or more | Force drying strongly recommended |
| 75mm | 90 days or more | Force drying strongly recommended |
Indicative only. Actual drying depends on temperature, humidity, ventilation and the build-up. Always confirm with a moisture test and follow the screed and covering manufacturers' data.
Week One: What To Do And When
- 1
0 to 24 hours
Keep the room closed. No draughts, no direct sunlight on the surface, no traffic at all. The screed is setting and rapid surface drying at this stage causes curling and cracking.
- 2
24 to 48 hours
Light foot traffic for essential access only, in clean soft-soled footwear. Still no through-draughts.
- 3
48 hours onward
Begin gentle ventilation. Open windows a little, or run background heat if the building is cold and damp, and build air movement up gradually.
- 4
5 to 7 days
Normal trade traffic on most sites. Protect the surface with breathable sheeting where trades are working overhead.
- 5
7 days plus
Point loads and stacked materials become acceptable. Force drying through underfloor heating can begin, following the manufacturer's commissioning profile.
- 6
Before covering
Sand off any laitance, vacuum thoroughly, then test moisture with a hygrometer against your floor covering manufacturer's stated limit.
Force Drying Through Underfloor Heating
Force drying is the fastest safe route to a covering-ready floor, and the most commonly rushed. Wait until the screed has cured, normally a minimum of 7 days, then follow the screed manufacturer's commissioning profile.
Start low
Begin around 20 to 25C flow temperature and hold until the floor is evenly warm.
Ramp gradually
Increase by roughly 5C per day to the design maximum, hold for several days, then step back down the same way.
Ventilate as you go
Heat alone pushes moisture into the air. Without ventilation it condenses back onto surfaces and drying stalls.
If your heating circuits were laid before the pour, our underfloor heating screed page covers the build-up and pressure testing we expect to see before we arrive.
The expensive mistake
Laying a covering onto a screed that is not dry is the single most common cause of failed tiles, lifting vinyl and cupped timber. Adhesive bond fails, moisture-sensitive finishes react, and the fix is to take the covering up again. A hygrometer test costs a fraction of that.
Moisture Testing Before You Cover
- Use a calibrated hygrometer box left in place for the full stated period, not a quick surface probe.
- 75 percent relative humidity or below is the usual threshold for most coverings.
- Around 65 percent or below for moisture-sensitive resilient finishes such as vinyl and some timber systems.
- Test more than one point, including the slowest-drying corner and the thickest part of the build-up.
- Your covering manufacturer's stated limit always overrides a rule of thumb.
Surface Preparation And Laitance
Where a fine laitance layer has formed on the surface, sand it off lightly and vacuum thoroughly before any adhesive or covering goes down. If the floor has taken knocks during the build, or the substrate was uneven to begin with, a thin skim of levelling compound brings it back to a covering-ready surface. Our screed finishing work is aimed at making that step unnecessary in the first place.
Drying And Aftercare FAQs
How long does liquid screed take to dry?
As a working rule, calcium sulphate flowing screed dries at roughly 1mm per day for the first 40mm, then slower beyond that, in normal indoor conditions. A 50mm floor is therefore commonly around 50 to 60 days to reach a covering-ready moisture level without force drying. A commissioning cycle through underfloor heating shortens that considerably.
When can I walk on liquid screed?
Light foot traffic is normally fine after 24 to 48 hours. Keep it to essential access only, in clean soft-soled footwear, and do not drag anything across the surface.
When can other trades work on the floor?
Most sites allow normal trade traffic after around 5 to 7 days, and loading such as stacked plasterboard or scaffold towers after 7 days at the earliest. Protect the surface with breathable sheeting rather than plastic, which traps moisture.
Can I use underfloor heating to dry the screed faster?
Yes, once the screed has cured, usually after 7 days minimum, and following the screed manufacturer's commissioning profile. Start low, typically around 20 to 25C, and raise in increments of about 5C per day up to the design maximum, hold, then ramp back down the same way. Never fire it up to full temperature on day one.
How do I know the screed is dry enough to tile or lay vinyl?
Test it, do not guess. A hygrometer reading of 75 percent relative humidity or below is the usual threshold for most coverings, and around 65 percent for moisture-sensitive resilient finishes. Your flooring manufacturer's stated limit always takes priority.
What is laitance and does it need removing?
Laitance is the fine layer that can form on the surface of calcium sulphate screed. Where it is present it should be removed by light sanding before adhesives or coverings go down, otherwise bond strength suffers.
Does drying time change in winter?
Yes. Cold, damp, unventilated rooms dry far more slowly. Keep the building weathertight, keep gentle background heat and air movement going, and expect longer than the summer figure.
Need A Floor That Dries To Programme?
We pour across South Wales and set out the drying plan with you before the wagon arrives. Quotes are subject to survey.