Liquid/Flowing Screed

Liquid screed is pumped to a datum set by laser levels to ensure that the finish is level and achieves SR2. Flowing screed can be applied at a lesser depth than sand and cement and can take foot traffic in 24 to 48 hours. As the screed is pumped into place there is less risk of damage from wheelbarrows and it is easier to place the screed on floors above ground level. The liquid screed can be pumped early in the build process allowing a longer time for drying and enabling carpenters to fix against a finished floor screed level.

In common with other screeds it is very important that good curing conditions are provided as soon as the flowing screed has been laid. Adequate protection from rapid drying or draughts should be provided for the first 48-72 hours but thereafter the relative humidity of the building should be low to allow moisture release from the screed and facilitate drying. Failure to provide the desired conditions can prolong screed drying times considerably and may lead to delays in the construction schedule.

Pre Application Points

• The area to be screeded must be made water tight to prevent leakage
• The polythene slip membrane installed over the insulation must be overlapped and sealed to prevent loss of screed
• Pipes or cables must be securely fixed to prevent floatation and lifting during application of the screed
• Best practice is to fill pipes floating whilst the screed is being poured
• ideal flow 230-250mm measure using the DIN1060 flow ring
• Minimum cover to pipes or cables must be 30mm
• If required surface laitance must be removed prior to commissioning underfloor heating
• Heating should be commissioned in accordance with BS1264:2001-4 clause 4.4 to accelerate force drying of the screed prior to application of the floor finish
• screed moisture content must be a maximum of 0.5% and 1.0% respectively prior to application of subsequent impermeable and permeable floor coverings.

Key Points of Liquid Screed

• Produced to a controlled flow able consistency to fully encompass heating pipes
• Elimination of voids resulting in uniform heat transfer and maximised thermal efficiency of the underfloor heating system
• reduced screed depth when compared to traditional sand cement screed minimising heat storage, resulting in a floor which responds rapidly to user requirements
• extremely low shrinkage - does not curl and minimises the risk of cracking
• does not require reinforcement
• increased productivity - 500-1000m2 per day can be easily achieved
• heating systems can be commissioned in accordance with BS1264:2001-4 clause 4.4, as early as 7 days after application of screed
• minimal thermal expansion (0.012mm/Mk)
• Excellent thermal conductivity
• no curing required
• ready for foot traffic in 24-48 hours

Laitance Removal

During the hardening process a friable film may form on the surface of the flowing screed slightly reducing the rate at which moisture can escape from the screed prolonging drying time. Removal of this film 1-3 weeks after application using the recommended equipment will open the surface.

Assisting The screed to Dry

Dehumidifiers

Dehumidifiers can be used as early as 7 days after placing of liquid screed to assist with drying. It is important that a closed system is employed to ensure that any moisture extracted from the environment during operation is removed whilst the warm air dries the screed. Failure to seal the water collection vessel will result in the moisture being re circulated delaying drying times.

Force drying of a liquid screed can be accomplished by commissioning of underfloor heating systems in accordance with BS1264: 2001 Part 4 clause 4.4 as early as 7 days after the screed has been placed. Raise system water temperature in 4-5oC increments from ambient to 20-25oC, maintain for a minimum of 3 days and then gradually increase the temperature again in 4-5oC increments too maximum operating temperature which should be maintained for a further 4 days (water temperature should not exceed 55oC for a calcium sulphate screed), prior to returning to ambient temperature in readiness to receive floor finishes. Please note that it may be necessary to commission and run the U/F heating system for greater than the 7 day commissioning period to enhance the drying. The time that is required for force drying is directly proportional to the age of the screed at the time of commissioning. In all cases it is important to remember that adequate ventilation is required to maintain good drying conditions. The screed must be dry before application of the floor finish and failure to follow this procedure prior to the application of subsequent impermeable floor coverings such as vinyl is likely to lead to failure of the floor finish at a later date. Subsequent to drying the screed by one of the above methods the residual moisture content must be determined using one of the approved test procedures to demonstrate suitability for acceptance of floor finishes (0.5% for impermeable finishes such as vinyl, and tiles and 1.0% for carpets) Once proven to be dry it is important that the surface of a liquid screed is protected from accidental spillages and leaking fixings (central heating pipes etc). Should these occur the exposed screed will require further drying to attain the required moisture content and in the worst case, full saturation of the screed drying times will be as with freshly placed screed leading to possible delays in the construction schedule. The information provided above is given in best faith as a guide to drying of liquid screeds and can be greatly influenced by individual site conditions.

If you have any questions about the liquid screed product please call us.

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