Stone Federation of Great Britain frequently suggests protecting the stone surface by using uncoupling membranes and movement joints.

Stone flooring has seen an increase in popularity over recent years, but can suffer from problems of cracking and debonding on different types of substrate, unless protective measures are taken. In fact, in its specifications and recommendations, the Stone Federation of Great Britain frequently suggests protecting the stone surface by using uncoupling membranes and movement joints.

Ian Knifton, Technical Manager at Schlüter–Systems, explains that while professional, trained, stone flooring contractors all know the principals and importance of crack suppression, there is a very high chance that installers who are not trained in laying stone are going to end up with failures.

Approximately 70 per cent of the domestic stone industry is made up of ceramic, porcelain and terrazzo fitters who have moved into the market thinking stone can be installed in the same way.

In the past a lot of stone was very hard marble or granite, which was relatively forgiving to movement stresses. But nowadays the trend is towards white limestone, in particular 600 mm x 600 mm x 10 mm, and fitters who aren’t professionally trained in stone don’t understand the characteristics of this thinner, more vulnerable material, which can crack easily when the substrate moves. So what can be done to stop stone installations from failing?

Stone must be fitted by trained installers, the design must be right, the stone used must be suitable for the application, uncoupling membranes must be used to prevent shear stresses being transferred from the substrate to the surface, and movement joints must be used to compensate for movement.

The Stone Federation’s code of practice brings together all the stone flooring elements of the different British Standards, including the use of uncoupling membranes.

An uncoupling membrane, such as Schlüter®-DITRA, installed over the substrate, with the stone anchored to the top of it, will neutralise movement and cracks in the screed, preventing any stresses being transferred from the screed to the stone surface.

How to install an uncoupling membrane

• After ensuring that the substrate is even and load-bearing, the bonding adhesive is applied with a 3 mm x 3 mm or 4 mm x 4 mm notched trowel (see illustration Stone Uncoupling 1). The type of bonding adhesive used depends on the type of substrate. It must bond to the substrate and mechanically anchor the fleece on the underside of the matting. Verify the compatibility of all materials before work begins.
• The fleece on the underside of the membrane needs to be solidly embedded into the adhesive so that its entire surface is bonded.
• Work the membrane into the adhesive, in just one direction, using a float or screed trowel. The stone can then be laid on top immediately afterwards, by anchoring an adhesive -- which must match the requirements of the stone surface -- into the cavities (see illustration Stone Uncoupling 2). The stone tiles are then fully embedded in the adhesive.

Ian Knifton is a Member of the Contract Flooring Association’s Manufacturers Committee, and the Stone Federation of Great Britain’s Technical Committee.

For more information contact:

Stewart Bint
T: 01530 813396
F: 01530 813376
e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Advice From Experts - Movement Joints