Programme and drying
Specifying realistic drying times and programme allowances for liquid screed
Drying time for liquid screed depends on depth, ventilation and site conditions, so a specification should set a testing regime rather than rely on a single fixed number of days.
Programmes are frequently drafted around a single figure quoted for drying, such as one millimetre per day, applied uniformly across the whole floor without reference to depth, ventilation or the time of year the pour takes place.
That approach causes more disputes on site than almost any other aspect of screed specification, because actual drying is governed by how readily moisture can leave the surface, not by a calendar date written into a Gantt chart months earlier.
A specification that instead states the testing method and the moisture criterion the floor must meet before covering, alongside a sensible provisional allowance for programme purposes, gives the contract a defensible basis for decisions if drying runs longer than hoped.
Why a single drying figure is unreliable
Published drying rates are typically based on reasonable site conditions: adequate ventilation, moderate ambient temperature, and no undue humidity. A site that is sealed up, unheated, or poorly ventilated over winter can see drying take substantially longer than the headline figure, while a well-ventilated summer pour may dry faster than expected.
Depth compounds this further, since moisture has to travel further to reach the surface in a thicker pour, and the relationship between depth and drying time is not linear. A specification that assumes the same daily rate regardless of these variables is setting up an unrealistic programme.
Building testing into the specification, not the programme
The more robust approach is to specify that the floor will be tested using an agreed method before any moisture-sensitive covering is applied, and that the programme date for covering is provisional pending that test result. This shifts the conversation from a disputed date to an objective measurement.
It also gives the contract a clear trigger for who is responsible for delay if drying takes longer than the provisional allowance, provided the specification is explicit about what caused the extended drying, such as inadequate site heating or ventilation outside the screeder's control.
Coordinating with underfloor heating commissioning
Where underfloor heating is installed beneath the screed, the heat-up and commissioning procedure recommended by the screed manufacturer often assists drying as well as protecting the floor from thermal shock, so the two processes are usually programmed as a single sequence rather than drying first and commissioning afterwards.
Drying times and programme — the points that decide it
- State the moisture testing method to be used, such as a calcium carbide test or an in-situ relative humidity probe, rather than leaving the criterion open to interpretation.
- Treat any quoted drying rate as a provisional programme allowance, not a guaranteed completion date, and say so in the specification.
- Note the factors that materially affect drying: screed depth, ambient temperature, relative humidity, and whether forced ventilation or dehumidification is provided.
- Where underfloor heating is present, drying and the heating commissioning sequence should be programmed together rather than treated as separate activities.
- Build in a decision point before the floor covering trade is due on site, so a delayed screed does not automatically compress the covering programme.
- Avoid specifying drying periods shorter than the manufacturer publishes for the depth and product in question, even under programme pressure.
- Consider whether accelerated or rapid-drying formulations are appropriate where programme is genuinely constrained, and specify them explicitly rather than assuming a standard product will dry faster than its datasheet suggests.
Drying times and programme — your questions
Building a programme around screed drying?
Tell us the depth, product and site conditions and we can give you a realistic provisional drying allowance.
Or call our landline on 01392 237700
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Depths & specification
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Underfloor heating & screed
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Depths & specification
Screed for heat pump systems
Depths & specification
Reinforcement and crack control
In short
Drying time for liquid screed depends on depth, ventilation and site conditions, so a specification should set a testing regime rather than rely on a single fixed number of days.
Building a programme around screed drying?
Tell us the depth, product and site conditions and we can give you a realistic provisional drying allowance.