Liquid Screed Tile Guide

Results from an independent test found that a 50 mm Screed with good airflow and ambient temperatures of 20 degrees could dry within as little as 25 days.

The test results commissioned by Gypsol are found here.

The British standard guide is all screed dries at 1 mm per day and 2 mm per day above 40 mm.

If the building has no windows open how can the moisture escape?

When the windows have to be kept closed then dehumidifiers should be used.

All screeds require priming with a suitable acrylic primer. This is done to stop the adhesives drying too quickly, so maximum strength is obtained.

If Cement based adhesives are to be used the floor will need priming until screed is no longer porous.

Anhydrite based adhesives generally only require 1 prime. We can recommend a complete range of adhesives for fixing wood or tiles.

Force drying of 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 4-5°C increments from ambient to 20-25°C, maintain for a minimum of 3 days and then gradually increase the temperature again in 4-5°C increments to the maximum operating temperature which should be maintained for a further 4 days.
• Maximum water temperature should not exceed 55°C for a calcium sulphate screed.
• Once commissioned the floor should be returned to ambient temperature to avoid any problems floor coverings.
• 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.
• It is extremely 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 tiles 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, wood flooring and tiles.
• 1.0% and for carpets.

Once proven to be dry it is important that the surface of the screed is not subjected to any spillages or leaks eg. plastering water buckets. 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.