Installing slate tiles on an Anhydrite Screed
Asked by... Nicholas Pearson from Bucks

The Question

Our builder has asked us to check how long we have to wait until we can install our slate tiles on a newly laid Anhydrite Screed

The Answer

1. It is imperative that the Anhydrite Screed has a moisture content reading of no more than 0.5% before tiling commences. Your builder will have to test this with a moisture reader so this is the first step that should always be taken.

The general rule of thumb for drying of screeds is
Less than 40mm thick = 1 day drying per mm
More than 40mm thick = 2 days drying per mm

For example a 60mm screed would take: 40 days
(40mm) + (20mm x 2 days) = 80 days at 20c?

2. Tiling must be fixed to an even sound surface free from all loose matter. If the surface is not even then an uncoupling membrane must be used. Ensure surface is first scarified to remove all surface laitance.

3. The surface must be primed with 2 neat coats of Granfix Acrylic Bonding and Priming Agent before tiling.

4. The tiles can then be fixed using a polymer modified adhesive such as 1 part flexible Rapid Set. If the floor contains piped underfloor heating the adhesive should be mixed with Granflex Plus additive.

5. A movement joint of 6mm must be left around the perimeter of the room and if the run of the floor is greater than 10m in length then movement joints must be inserted in accordance with BS 5385 - The Code for the Installation of Ceramic Wall and Floor Tiling.

6. The heating should be left off for 7 days after tiling and grouting has finished and then turned up gradually over a period of a further 7-10 days.

- asked before 2013
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