Liquid Screed Aftercare
After we leave, you’ll need to know how to take care of your
new screed and prepare it for your chosen floor covering.
Please see our easy to follow, step-by-step guide below which covers
everything including drying, laitence removal and priming.
Alternatively, press this button to download our full preparation and aftercare guide .
Liquid screed can usually accept light site traffic after about 24 – 48 hours. It is sometimes possible to traffic the morning after the previous installation. Full site traffic should be avoided for at least 2-3 days.
Where heavier site traffic is expected, it is advisable to temporarily protect these areas with plywood sheets, which should be removed in good time to permit adequate drying.
It is essential that the material is allowed to cure undisturbed for the first 24-48 hour period. The floor area should be closed to all traffic.
Traditional curing procedures using impermeable membranes are not necessary but rapid loss of moisture should be avoided during the first 24-48 hours. Where windows and/or doors are not installed, a temporary provision must be made using appropriate materials.
Direct sunlight must be avoided during the first 24-48 hour curing period. Windows and glass doors with a southern aspect should be covered temporarily for this period. After the first 24-48 hours of curing doors and windows may be opened.
It is important to note that drying times relate to ambient humidity, temperature and number of air changes. In general, liquid screed installed as an un-bonded system dries at a rate of 1mm per day for the first 40mm of depth and 0.5mm per day for any depth over and above this. This is provided a temperature of 20 degrees celcius is maintained and 65% relative humidity.
Where drying temperatures are high and humidity is low, drying time will be less. Unlike conventional cement / sand screeds, dehumidifiers may be used to accelerate drying. These should only be used 2 to 5 days after placing.
Where under floor heating is installed this can be used to decrease drying times but should only be used after the first 7 days. The heating system temperature should be built up gradually at a rate of 5 degrees celsius per day.
Prior to the installation of a floor covering, liquid screed must have dried to an approved level. For moisture sensitive coverings the code of practice value is stated as 75% relative humidity, which equates to 0.5% moisture content by mass. Below this value impermeable floor finishes may be applied.
Avoid water ingress to completed screeds and arrange to dry out accidental ingress as soon as possible. The screed may suffer a minor loss of strength if it becomes wet however, this strength will generally be regained when it dries out.
Open windows on all sides of the building in order to achieve good cross ventilation and air changes thus accelerating the drying out process. A typical 40mm thick screed can be expected to dry to 0.5% moisture content in 40 days under ideal conditions. This can however be greatly affected by actual conditions.
Unlike cement based screeds, calcium sulphate screeds can be forced dried, by commissioning the underfloor heating system (if applicable) or by utilising a dehumidifier.
Commissioning Underfloor Heating:
After 7 days of installation of the liquid screed, the commissioning process starts with a water temperature (UFH manifold) of 25°C, which is maintained for three days. The water temperature is then raised to the maximum value (max. 55°C) and kept at this level for at least 4 days.
Allow for plenty of ventilation by opening windows on each side of the building. Please note: it is essential that the building receives sufficient air changes in order to achieve low air humidity ( 65% RH). Continue with above procedures for approximately 4 weeks or until a moisture content of 0.5% (tiling/vinyl) or 1% (carpet) is achieved. Please refer to a moisture testing expert or flooring installation company for further details.
After 7 days of the installation of the liquid screeds, introduce heat and utilise a dehumidifier with enough capacity for the m3 area of the building. Use several dehumidifiers if required. Keep windows and doors closed in order for the dehumidifier to work efficiently.
Continue with above procedures until a moisture content of 0.5% (tiling/vinyl) or 1% (carpet) is achieved. Moisture testing by Hair Hygrometer can be arranged upon request at an additional charge.
Once the anhydrite liquid screed has been laid, the thin layer of laitance left as any surface water evaporates should be removed by sanding the floor approximately 7-10 days after application. This will not only help the drying out process, but will also provide a stable surface on which to tile onto.
A calcium sulphate compatible primer should be applied to the floor once the floor has completely dried to the recommended moisture levels at which point a floor covering can be applied. It is also important that any adhesive used is anhydrite / calcium sulphate compatible. Please check with your chosen suppliers to ensure that this is the case.
