Liquid Screed Drying Time – Prevent Flooring Failures and Site Delays
How long does screed take to dry? Liquid screed is dry enough for foot traffic in 24 to 48 hours. Total drying time, however, (before you lay final floor coverings), depends entirely on your screed base.
For standard anhydrite (calcium sulphate) screeds, calculate 1mm per day up to a 40mm depth, and 0.5mm per day for anything thicker. For advanced cementitious liquid screeds, that timeline drops drastically – often drying completely within 14 to 21 days regardless of depth.
At Capital Screeding, we supply and install high-performance liquid floors across London, Essex, and the South East. Guessing your floor’s curing window leads to failed moisture tests, ruined adhesives, and blown schedules. If you are coordinating multiple trades, you need to know exactly when that slab can handle foot traffic and when it’s ready for the final finish – that’s exactly what we cover below.
What Affects Liquid Screed Drying Time?
A slab poured in a well-ventilated room in mid-summer cures on a completely different timeframe than one sealed inside a cold, damp building in December. Moisture has to evaporate out of the screed and then escape the building entirely. If you leave a site locked up with zero airflow, the air saturates, and the drying process stops altogether. Controlling your timeline means controlling your site’s climate once the liquid screed is poured.
How to optimise your screed drying time:
- Depth – Take care to stick to your structural minimums. Every unnecessary millimetre added to the floor depth adds a full day to your flooring handover schedule.
- Airflow – Trapped moisture stalls your timeline. Open internal doors and windows to force a steady exchange of fresh air across the slab surface once the initial 48-hour cure completes.
- Thermal Regulation – Avoid freezing conditions. Keep the building warm enough to drive water up to the surface, but never use direct radiant space heaters aimed at the floor, as this causes uneven drying and cracking.
How to Safely Speed Up Liquid Screed Drying Time
If you’re working to a tight handover deadline, you won’t be able to wait weeks for a slab to dry naturally. The moisture will need to be forced out. The wrong way to do this is by rushing this process with unregulated heat. That will warp, curl, or crack the floor.
To safely reduce your cure time, you need both underfloor heating commissioning and mechanical dehumidification starting exactly 7 days after the pour.
Step 1 – 7-Day Cure – For the first 7 days post-pour, have the underfloor heating completely off. Turning it on will shock the wet slab, causing structural cracking and major surface failures.
Step 2 – Day 8 – Introduce Baseline Heat – On the eighth day, turn the heating system on. Set the flow water temperature to exactly 25°C (or ambient site temperature if it is lower). Run the system at this baseline for 24 hours to stabilise the slab core.
Step 3 – Days 9 to 13 – Increase the Temperature – Increase the flow water temperature by exactly 5°C every 24 hours. Daily increments should look like this: Day 9 at 30°C, Day 10 at 35°C, Day 11 at 40°C, up to a maximum design operating temperature of 45°C or 50°C.
Step 4 – Days 14 to 20 – Maintain Peak Heat – Keep the system at its maximum temperature for 7 consecutive days. This sustained thermal pressure drives the residual water out of the screed and up to the surface.
Step 5 – Days 21 to 25 – Lower Heat and Remove Moisture – Reverse the process. Drop the flow water temperature by 5°C every 24 hours until you hit the original baseline. Use commercial dehumidifiers during the entire cycle to suck the moisture in the air out of the building.
Removing Laitance is Essential to Evaporation
During the first 24 to 48 hours after a pour, excess water naturally rises to the top of an anhydrite screed. As this surface water evaporates, it leaves behind a milky, brittle skin made up of very fine aggregate and chemical binder particles. This is called laitance, and it quickly cures into a hard, glassy crust that covers the entire floor.
Force-drying without removing this layer will be a complete waste of energy. The glassy film acts as a solid vapour barrier, locking moisture deep within the screed and stopping any evaporation from taking place.
You should mechanically sand the floor to strip this skin away precisely between day 7 and day 11 post-pour. Sanding during this specific timeframe opens the damp core of the slab directly to your site’s airflow, allowing the floor to breathe and it can then dry according to the schedule laid out. You may find our guide to removing laitance useful.
Not All Screeds Form Laitance
Laitance is primarily an anhydrite problem. If you’re using a cementitious flowing mix, you can forget the 7-to-11-day sanding rule. Laitance will not form on:
- Cementitious Flowing Screeds (e.g., Cemfloor) – These cure via a traditional cement hydration process, leaving the surface clear of any glassy vapour barriers.
- Specially Formulated Low-Laitance Binders – Premium anhydrite mixes engineered specifically to suppress surface residue during the initial chemical set.
Liquid Screed Drying – FAQs
Beyond the basic depth calculations and thermostat settings, there will be unexpected on-site challenges that will alter your flooring timeline. We’ve compiled the answers to these kinds of issues that our installation teams come across daily across London and Essex build sites.
Never rely on visual inspection or electronic pin meters; they only measure surface moisture. If you want to protect your flooring warranty, you have to perform a structural hygrometer test or a calcium carbide test. For moisture-sensitive finishes like engineered wood, luxury vinyl tiles (LVT), or resin, the relative humidity (RH) reading must sit below 75% (or 0.5% moisture content by weight) before you lay a single floorboard.
If you cannot wait for an anhydrite floor to dry naturally, you can use a specialised epoxy damp-proof membrane to seal the residual moisture. The floor must still reach a minimum threshold, though – under 92% RH – and you’ll need to use a water-tolerant primer designed for calcium sulphate bases.
If you trap moisture underneath an impermeable layer like vinyl or laminate, the water has nowhere to go. So it will accumulate under the flooring material. This causes adhesive hydrolysis (where the glue liquefies and fails), warps timber boards, bubbles vinyl sheets, and creates a breeding ground for subfloor mould.
If the cured slab suffers water ingress from a burst pipe or open window, the drying clock will need to be completely reset. Anhydrite screed acts like a dense sponge; it re-absorbs moisture rapidly. If this occurs, shut down the site, extract standing water immediately, and restart your underfloor heating force-drying process from day one once the leak is sealed.
Talk Directly to a London Screed Specialist
Eliminate the possibility of subfloor failures and adhesive issues. Call the Capital Screeding team directly to map out your installation and drying strategy for your next residential or commercial project – 020 3369 3396
