Gypsum based screeds (Anhydrite Screeds) have become very popular due to a lot of people opting for underfloor heating and they are sold on the benefits they have over sand/cement screeds. They are very economical to the builder and are often put forward as the best option on site. They are suitable for use with under-floor heating as long as pipes/elements are covered by 25mm. However there are a few general guidelines that should be adhered to in order to avoid problems in the future.
It must be:
• Dried out to 0.5% moisture by weight.
• Remove all laitance to expose the black aggregate in the screed.
• Underfloor heating MUST be commissioned (this is the same for all screeds)
• Before tiling commences, turned off for 48 hours to allow floor to cool down.
• Primed with ARDEX P51 Acrylic primer once prepared.
Remove all Laitance
Primed with an Acrylic Primer
When Cement based products and gypsum based products come in contact with each other a chemical reaction known as Ettringite occurs. This is why a separating layer of an acrylic primer like ARDEX P51 or BAL APD should be used and applied to the dried screed. The Acrylic primers should always be brushed in never rolled to ensure the primer is pushed into the surface of the screed.
ARDEX Ireland provide a site surveillance for all our customers we will assist you in determining the amount of time and preparation required for your screed to be ready to accept a floor covering.