Installing tiles and wood flooring onto Anhydrite Liquid Screed

 

Many issues have been raised in the past about Calcium Sulphate Screeds when it comes to fixing the final floor covering.

The same problems happen to traditional sand and cement screed as well.

 

Make sure the Screed is dry

 

  • The time it takes for any screed to dry is purely based on surrounding conditions.
  • If there is good airflow with a reasonable temperature the screed will dry a lot fast.
  • Run the Underfloor Heating through a complete cycle.

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.

 

Remove surface laitance

 

Removal of surface laitance is very important. 

The Screed will have a film of laitance once it has dried, this can be removed by brushing between 18-36 hours

If the surface of the screed has any loose material for example plaster, this will need to be removed by mechanical means.

An orbital floor sander is the best method for achieving this.

 

 

 

Priming

 

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 dry liquid screed boiler

 

Force Drying Anhydrite Screed

 

You can run dehumidifiers after 7 days. This must be done in a closed loop so the building must be sealed from the outside completely.

 

You can also run the underfloor heating through a full heat cycle to dry the screed.

The use of a temporary electric boiler is the best way to dry the screed allowing construction to be completed without delay.

Please speak to one of our team if you would like to hire a boiler.

 

 

 

 

 

 

 

Underfloor Heating commissioning procedure for Anhydrite Screed.

 

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.

 

Tile Adhesives 

We recommend Tilemaster Adhesives.

 

tilemaster