How long does a cement screed take to dry?

As a rule of thumb, cement screed (CT) needs about one week per centimetre of thickness up to 4 cm under favourable room climate; every additional centimetre takes disproportionately longer. A 5 cm screed realistically needs 6 to 8 weeks — considerably more in poor conditions. Only the measured moisture value is binding, never the calendar.

Does calcium sulphate flowing screed (CAF) dry faster than cement screed?

CAF usually releases moisture faster in the first phase but is more sensitive to high air humidity and rewetting. For both screed types the room climate is decisive: without air exchange, drying stalls regardless of the material.

Can drying be accelerated?

Yes — through controlled ventilation (dry outdoor air, shock ventilation), moderate heating, and for heated screeds through the covering-readiness heating protocol. Dehumidifiers help when room humidity is persistently high. Drying a cement screed too quickly in the early phase can cause curling and cracks.

How do I know when a CM test is worthwhile?

Continuous moisture monitoring inside the screed shows the drying curve in real time. When the measured value approaches the threshold range, the CM test is scheduled — instead of testing on suspicion and paying for failed measurements.

What happens if flooring is installed too early?

Trapped residual moisture leads to blistering, debonding, discolouration, mould or swollen parquet depending on the covering. Remediation costs usually far exceed the cost of waiting — which is why covering readiness must be proven.

Screed drying time: what determines it and how it progresses

What determines screed drying time: screed type, thickness, room climate. Typical curves for CAF and CT, with reference to DIN 18560 / EN 13813.

Screed drying time is one of the most common causes of delays in interior fit-out — and one of the hardest quantities to plan. Anyone counting only calendar weeks is regularly wrong. This article shows which factors actually govern drying, what typical curves look like for calcium sulphate flowing screed (CAF) and cement screed (CT), and what measurably shortens or prolongs drying.

The four governing factors

1. Screed type. Cement screed (CT per EN 13813) binds water chemically and releases surplus mixing water over weeks. Calcium sulphate flowing screed (CAF) carries less surplus water and often dries faster initially, but is more sensitive to rewetting — once moisture is reabsorbed it is released only slowly, and permanent saturation attacks the structure.

2. Thickness. Drying time grows disproportionately with thickness: moisture from deeper zones must diffuse upwards through layers that have already dried. For CT the rule of thumb is roughly one week per centimetre up to 4 cm — every further centimetre counts nearly double. A 7 cm screed therefore needs not 7 but more like 10 to 13 weeks under good conditions.

3. Room climate. A screed only dries if the room air can absorb and remove moisture. Favourable conditions are roughly 15–22 °C and 40–65 % relative humidity. At 80 % humidity and low temperatures, drying effectively stalls — the screed “waits” without showing it.

4. Air exchange. The absorbed moisture has to leave the building. Without ventilation the room air saturates within hours, after which nothing happens. Regular shock ventilation or controlled air exchange beats any temperature increase without air exchange.

Typical curves: CAF vs. CT

For both screed types the drying curve is not a straight decline but a three-phase curve: a fast initial phase (surface moisture evaporates), a long diffusion phase (core moisture migrates upwards) and a flat final phase just before equilibrium moisture.

Cement screed (CT) starts with a large water surplus. Release is high in the first days; diffusion then sets the pace. Critically, in the flat final phase the moisture value moves only slowly — this is exactly where room climate decides whether the last few tenths of a percent take weeks or months.

Calcium sulphate flowing screed (CAF) reaches the diffusion phase earlier. Under good conditions a 4 cm CAF can be ready for covering after [PLACEHOLDER: typical duration from pilot data]. In return, CAF responds visibly to moisture events: a thunderstorm through an open window or subsequent wet trades (plastering, painting) set the curve back noticeably.

In our pilot projects with continuous in-material measurement the difference is clearly visible: the moisture curve in g/m³ — comparable with the CM reference — shows when drying stalls and when it resumes. [PLACEHOLDER: example curve/figures from pilot project CAF C25 vs. CT C25]

What shortens drying

Controlled ventilation: shock ventilation with dry outdoor air, especially in winter (cold outdoor air is absolutely dry and absorbs a lot of moisture once warmed).
Moderate heating: 18–22 °C room temperature keeps diffusion going. For screeds on underfloor heating, covering-readiness heating per protocol is the strongest lever — see the article on drying heating.
Dehumidifiers: useful when room humidity stays above ~65 % or ventilation is impossible. Important: keep windows closed, otherwise you are drying the outdoor air.

What prolongs drying

Subsequent wet trades: plastering and painting return litres of water to the room — the screed reabsorbs part of it.
No ventilation after building closure: especially in airtight new builds without occupants, drying stalls for months.
Low temperatures: below 10 °C diffusion slows drastically.
Covering the surface too early: foils, site protection or stored material on the screed block the evaporation surface and create local moisture pockets.

The calendar is not a measurement

All rules of thumb are only starting estimates. Whether a specific screed in a specific building is ready for covering is decided by measurement alone — the recognised proof is the CM test per DIN 18560 (analogously regulated in the SIA context). Continuous in-material monitoring does not replace the CM test, but shows continuously where the screed stands in its drying curve: it makes clear when a CM test is worthwhile and prevents flying blind in between.

To measure the curve in your own project, you can test the system in a pilot project — matching specification templates are available for download.

Frequently asked questions

How long does a cement screed take to dry?: As a rule of thumb, cement screed (CT) needs about one week per centimetre of thickness up to 4 cm under favourable room climate; every additional centimetre takes disproportionately longer. A 5 cm screed realistically needs 6 to 8 weeks — considerably more in poor conditions. Only the measured moisture value is binding, never the calendar.
Does calcium sulphate flowing screed (CAF) dry faster than cement screed?: CAF usually releases moisture faster in the first phase but is more sensitive to high air humidity and rewetting. For both screed types the room climate is decisive: without air exchange, drying stalls regardless of the material.
Can drying be accelerated?: Yes — through controlled ventilation (dry outdoor air, shock ventilation), moderate heating, and for heated screeds through the covering-readiness heating protocol. Dehumidifiers help when room humidity is persistently high. Drying a cement screed too quickly in the early phase can cause curling and cracks.
How do I know when a CM test is worthwhile?: Continuous moisture monitoring inside the screed shows the drying curve in real time. When the measured value approaches the threshold range, the CM test is scheduled — instead of testing on suspicion and paying for failed measurements.
What happens if flooring is installed too early?: Trapped residual moisture leads to blistering, debonding, discolouration, mould or swollen parquet depending on the covering. Remediation costs usually far exceed the cost of waiting — which is why covering readiness must be proven.