Conscious uncoupling

David Wilson of BAL takes a look at why specifying an uncoupling system is a sensible option for making a floor tiling installation as efficient as possible

With today’s requirements for faster installation of tiling and the use of more demanding substrates, ‘uncoupling’ matting and membrane are being used more frequently and in some cases are a necessity. Uncoupling principles have actually existed for centuries, with the Romans being the first documented users of the building process, which incorporated an “uncoupling” method. These early practices used a mud bed to separate the substrate (then a two-inch thick layer of packed and flattened sand and cement) and the tiles. Both systems use the separating layer to provide an uncoupling buffer between the tile and the substrate, enabling the substrate to move independently to the tiles.

Modern uncoupling system methods have improved dramatically, but the same basic principles still apply for today’s uncoupling mat systems, which are now in common use on floor tiling installations onto a variety of different substrates. Coming in many forms, from thin, lightweight matting, to traditional cavity mat and floating systems, they give architects and contractors peace of mind when designing floor tiling installations. Designed to provide a buffer layer when tiling onto floors, they protect against a variety of problems that can cause tiles to crack or de-bond. One common problem is the potential for the substrate to contract or expand.

In particular, newly laid sand: cement screeds or concrete may contain large amount of moisture, which as evaporates, causes the screed to shrink. However, all substrates will expand and contract naturally due to humidity and/or temperature fluctuation, and this is especially true where under floor or under-tile heating has been installed. What’s more, certain water-sensitive substrates, such as anhydrite screeds (or calcium sulphate) will lose their cohesive strength if they get wet. Wood is a hygroscopic material, and this, therefore, increases the potential risk of dimensional changes occurring within boards due to moisture expansion and drying shrinkage movement, resulting in lateral movement stress being generated between the board background and the rigid ceramic tile finish.

Any movement, whether shrinkage or expansion, can cause stress cracks that can transfer through to the tiled surface, causing the tile to either fracture, or de-bond from the background. Uncoupling matting helps to prevent these lateral stresses from transferring through to the tiled layer, by absorbing these stresses and transferring them evenly over the floor. Matting also has the ability to bridge static cracks i.e. shrinkage cracks up to 2 mm wide and joints between sheet & board backgrounds.

Another of benefit of modern matting systems is their suitability for waterproofing. In areas subject to moisture exposure where additional movement can occur, uncoupling mats can be used in conjunction with tanking products to ensure a combination of waterproofing and uncoupling can be achieved. When waterproofing or no priming of the matting is required, such as with a waterproofed uncoupling mat, do ensure that the membrane and liquid coating can interface with the chosen drain. While the uncoupling membrane was originally devised for the installation of ceramic tiles, uncoupling systems are now recommended for use when tiling natural stone on all substrates. Importantly, uncoupling mattings are recognised by most floor trade associations related to the tiling industry as a major benefit.

Both the TTA and the Stone Federation of Great Britain recognise the value of using these products and also gives reference to their use in BS 5385 part 3, 4 and 5. Non-cavity uncoupling mat systems are perfect for use in commercial or domestic environments, with some products actually capable of accepting loads on floors immediately following installation, due to having a condensed profile with almost no compression. This makes them perfect for car showrooms, hospitals, and shopping centres, areas where vehicular traffic is present, and areas with mosaic tiles. Relatively new to the UK market, floating mats are loose laid onto the substrate and as such provide ‘true’ uncoupling – similar to the ancient use of sand as a buffer layer between the tile and substrate. The use of a floating uncoupling system seriously reduced preparation time and project cost – particularly when equipment such as floor grinders and sanders have to be purchased or hired in to remove any laitance on screed which could react to the adhesive used with bonded mat systems.

Floors often need additional priming before accepting any cementitious tile adhesive. Floating systems also take away the need for the screed to be fully cured, because any residual moisture in the substrate is evenly distributed through a system of channels and then drawn off through the perforations in the mat via the grout joints. In this way, substrates that are still damp are not encapsulated.

David Wilson is UK head of technical standards and information at BAL