Understanding Liquid Screed Drying Times: Essential Durations and Conditions

When a liquid screed is poured on a Friday morning, many homeowners might think they can lay their flooring by the following Monday. This is a common misconception. The drying time of liquid screed is frequently underestimated, leading to costly mistakes such as warped flooring or peeling tiles, which can jeopardize warranties. However, with the right information, these timelines can be accurately predicted.

Different factors come into play depending on the type of screed used, its thickness, and whether underfloor heating is involved. Here’s what you need to know before scheduling additional tradespeople on-site.

Basic Drying Times for Liquid Screed

Anhydrite Screed vs. Cement Screed

There are two primary categories of liquid screeds available, each exhibiting distinct behaviors regarding moisture retention:

• Anhydrite Screed (calcium sulfate-based) dries faster on the surface but remains sensitive to residual moisture below. It reaches foot traffic resistance in 24 to 48 hours, but complete drying takes significantly longer.
• Cement Screed (or fluid concrete) handles ambient humidity better, although its initial setting time is slightly slower. After 48 to 72 hours, depending on thickness, it can tolerate cautious foot traffic.

A common guideline from manufacturers suggests one week of drying for each centimeter of thickness for anhydrite screed under normal conditions (20 °C, humidity below 65%). Thus, a 5 cm screed would require approximately 5 weeks before the final flooring can be installed.

1 sem/cm

Basic rule for anhydrite screed at 20 °C — approximately 5 weeks for 5 cm thickness

Drying Times Based on Thickness

Typical thicknesses on construction sites range from 35 mm (minimum for underfloor heating) to 80 mm (in cases of significant leveling). Here are the indicative drying durations:

| Thickness | Anhydrite Screed Drying | Cement Screed Drying | |-----------|-------------------------|----------------------| | 35 mm | 3 to 4 weeks | 3 to 5 weeks | | 50 mm | 5 weeks | 5 to 7 weeks | | 70 mm | 7 to 8 weeks | 8 to 10 weeks |

These durations assume proper ventilation and stable temperature. Any deviation from these conditions will prolong drying times.

⚠️ Factors That Disrupt the Schedule

Temperature and Ambient Humidity

The drying of liquid screed is a physical process, not a chemical one, primarily involving the evaporation of water. Therefore, factors like wind, heat, and humidity in the area are just as critical as the product formulation.

• Below 5 °C, anhydrite screed dries almost not at all. Winter construction sites without supplementary heating are a common pitfall.
• Above 30 °C with strong direct sunlight, the surface may crust too quickly, leading to shrinkage cracks.
• Humidity levels exceeding 75% significantly slow down evaporation — drying times can double during persistent heavy rains or in unheated spaces in autumn.

⚠️ Important to Remember

Anhydrite screed is incompatible with free water. Any infiltration or rising moisture during the drying phase can cause irreversible swelling. Ensure the supporting slab is watertight and seal peripheral joints before pouring.

Underfloor Heating: A Special Case

For hydraulic underfloor heating, the heating protocol is standardized and non-negotiable. It begins only after the initial drying period — never before.

1. Wait at least 21 days Regardless of the manufacturer, heating does not commence until 21 days after pouring (often 28 days is recommended).
2. Gradually increase temperature Start at 25 °C for 3 days, then increase in increments of 5 °C until reaching the maximum operational temperature.
3. Lower the temperature before flooring installation After the accelerated heating phase, reduce to 18-20 °C and measure residual humidity before any flooring is laid.

🎯 How to Measure Residual Humidity Before Installation

The Threshold to Not Exceed

Simply feeling the screed with your hand or placing a cardboard box on it does not provide an accurate measurement. Only a carbide hygrometer or a CM probe (Carbide Method) can yield reliable values. The thresholds accepted by French DTUs are clear:

• Anhydrite Screed: residual humidity must be below 0.5% CM before any flooring, and 0.3% for glued parquet.
• Cement Screed: below 2.5% CM for tile installation, and below 2% for soft coverings.

“A parquet installed on an anhydrite screed at 0.8% CM instead of 0.5% can swell by 3 to 5 mm over a 30 m² area — and the flooring installer is not responsible if this measurement hasn’t been taken.” — Common practice reiterated by flooring installer unions (UCPA)

Accelerating Drying: What Actually Works

Several techniques can reduce drying times without compromising screed quality:

• Cross Ventilation: Opening windows on opposite sides creates airflow. This works best when combined with a professional dehumidifier (rental cost: €40 to €80/day).
• Supplementary Heating: Maintaining a temperature of 20-22 °C significantly speeds up evaporation. Be cautious with convectors that only dry the air and not the screed deeply.
• Leveling Cutbacks: Some manufacturers offer bonding primers that allow for flooring installation a few days earlier — check product technical sheets for verification.

What to avoid: abruptly heating to 30 °C by day 3 or covering the screed with plastic to “protect” it — this traps moisture and reverses the desired effect.

✅ Key Takeaway

Ventilation + stable temperature between 18 and 22 °C + CM measurement before installation: this triptych prevents most issues related to liquid screeds. Time-saving on the schedule never outweighs the risk of needing to redo an entire flooring installation.

Liquid Screed and Construction Scheduling

Organizing Trades Without Delaying the Project

The drying time of liquid screed often becomes a bottleneck in renovations. Here are some guidelines to organize the schedule without losing time:

• Day 1 to Day 2: Light installation of lightweight frames (without heavy tools or carts) is possible.
• Day 7: Light scaffolding can be installed, allowing work at height (ceiling painting, electrical work in conduits).
• Day 21 to Day 28: Initiate the heating protocol for underfloor heating.
• Day 35 to Day 56, depending on thickness: CM measurement and, if compliant, installation of the flooring.

An experienced tiler will tell you: it’s better to postpone the installation by a week than to redo 50 m² of tile that has come loose six months after delivery. Drying times are not mere suggestions — they are physical parameters.

💡 Our Advice

Always include a clause in your contract with the flooring installer for verifying residual humidity levels with a CM probe before proceeding. This protects both the client and the tradesperson in case of future disputes.

Special Case of Large Areas

For areas exceeding 100 m², liquid screed is typically poured with expansion joints. These joints do not affect the overall drying time but do condition the flooring installation: some large-format tiles require that the joints be treated (soft joint) before installation, adding a step to the schedule.

In office or commercial spaces — where areas often exceed 500 m² — pouring is done in zones, allowing for follow-up drying in each area, progressively freeing spaces for subsequent trades. Monitoring with data loggers (like the Testo 176 H1) provides hourly documentation of drying, which can be useful in case of disputes regarding timelines.