After Your Liquid Screed Surrey

After Care

After Your Liquid Screed is Poured

It is essential that the screed is closed to any foot traffic for the first 24-48 hours, to enable it to cure undisturbed.
Adequate protection must be provided from rapid drying or draughts for the same first period of 24-48 hours.
Cure time will depend on the thickness, type of screed being used and the atmosphere of the room it is being placed, though it is typically 1mm per day up to 40mm. See below for more information.
Usually, we recommend between 24-48 hours before you can walk on our screed. We can give you a clearer answer once we know the details of your project, so please contact us to discuss the details of your screed requirements.
4 Factors should be considered when drying your screed:
Room temperature – Should be kept warm and as well ventilated as possible to aid the drying process. This will assist the screed to dry through improved evaporation. **Remember no draughts!
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.
Humidity – It is important to provide good to ensure low humidity is achieved as high humidity will slow the drying process.
Screed Temperature – Underfloor heating can be commissioned at 7 days. Commissioning the screed raises the vapour pressure, greatly improving the drying rat of the screed. This should be combined with good ventilation.
Moisture – The floor should be protected from moisture ingress to prevent rehydration which will delay the drying process dramatically. Where windows and/or doors are not installed, a temporary provision must be made using appropriate materials to ensure the room is weather tight.

Drying Time

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 Celsius 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.

During the Drying Out Period (after 24 – 48 hours)

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 be regained when it dries out. Open windows on all sides of the building 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 affected by actual conditions.

Forced Drying

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 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.

Using a Dehumidifier

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 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.

Floor Covering Preparation

Liquid screeds – just like all other screeded surfaces – need to undergo appropriate preparation and finishing before the subsequent bonded floor coverings are applied. This is to ensure the best possible adhesion and a flawless finish; laitance removal is performed prior to application of the floor covering. In the absence of laitance removals, the risk of de-lamination of the new floor covering is significantly higher.

The preparation of all liquid screeds ready for floor coverings can vary depending on 4 areas:

Laitance / Sanding
Drying and moisture testing
Underfloor Heating Commissioning
Priming

What is Laitance?

Laitance is the crumbly coating of fine particles which forms on the surface of a screed floor during the curing period. Its presence indicates that excess moisture is finding its way to the surface, which could inhibit the rapid drying times normally associated with liquid screed. Due to the prop-erties of the laitance, it has the potential to cause serious problems when flooring is laid directly on top, without first removing this residual layer, as the layer is too weak to hold the finish.

Removing Laitance Rom Screed

The appropriate treatment for laitance removal / floor sanding should be carried out 7-14 days af-ter the application of screed. The use of a sanding machine is also known as ‘abrading’. This means that the surface is scoured to ensure the removal of all dust and fine particles clinging to the screed finish.

Due to the potential dangers associated with silica inhalation, it is strongly advised that laitance removal is carried out by trained professionals with the appropriate machinery and safety gear. In addition, attempting to remove laitance without sufficient experience and expertise can cause
severe damage to the surface of the screed.

Once the sanding is complete, all excess dust is removed using an industrial vacuum cleaner. The
resulting surface is now durable, and stable enough for the installation of the flooring finish. We would always recommend to clients that a primer is applied to the screed surface before tile adhe-sive is applied.

We offer efficient, cost-effective approach to screed sanding and laitance removal surfaces to all our clients, please contact us to arrange.

Why Remove Laitance?

Failure to remove laitance represents one of the most common causes of flooring installation fail-ures. When laitance appears following the concrete or cement screed curing process, the resulting crust is unsuitable for safe and reliable adhesion to the final floor covering.

Depending on the material used, laitance varies significantly in thickness, ranging from a thin coat of dust to several millimetres or more. The thicker the laitance, the more important it is to ensure it is comprehensively and professionally removed.

Moisture Testing

As with all screeds, in good conditions Gyvlon has a natural drying time of 1mm per day up to 40mm and 0.5mm after that, drying times can be greatly affected by site conditions so it is advised that the atmosphere is kept as warm and dry as possible. Commissioning the UFH and/or using dehumidifiers can greatly improve the figures above, prior to coverings the screed moisture must be tested using either a hair hygrometer, carbide bomb or oven test and be below 75% RH (0.5% Moisture).

NB: It may be possible to use Gypsum based products at 87% RH (1.5% Moisture), manufacturers must be consulted. (Please refer to the Gyvlon ‘Moisture Testing’ Datasheet)

Underoor Heating Commissioning

Where under floor heating is used it must be commissioned and run prior to floor coverings regardless of how dry the screed maybe, this is in line with CFA, TTA, Vinyl/Tile Manufacturers and UHMA guidelines.

This process forces additional moisture from the screed and conditions it to thermal movement prior to coverings, typically the commissioning cycle is 21 days and can be started as early as 7 days with Gyvlon screeds.

The guidelines state that the underfloor heating should be:

Commissioned at ambient floor temperatures, approx. 20 degrees (or lowest manifold temperature).
This temperature should be maintained for 24 hours, then raised by up to 5 degrees per 24 hours thereafter until the optimum running temperature is reached (Maximum 50 degrees).
This should then be maintained for 7 days prior to the temperature being reduced by 5 degrees per day back to the starting point.
The system can be turned off and allowed to cool for 48 hours prior to moisture testing by digital hygrometer.

Contact Us for Advice on Screed Type and Pricing

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