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They have already become the standard for professional tilers – and the use of decoupling mats definitely has advantages for do-it-yourselfers too. Because by decoupling from the subfloor, consequential damage during tile installation can be reliably prevented. In this article you can read about when a decoupling mat makes sense, what functions it fulfils and how best to lay tiles decoupled.

Why do you need decoupling mats at all?

Tiles are extremely popular as floor coverings: they score points with their attractive appearance, are robust and hard-wearing – and are in principle suitable for laying on almost any surface. In principle, it is quite common to bond tiles directly to the screed, but it is often advisable to lay them separately. The reason for this is as simple as it is serious:

As building materials expand and contract again with temperature fluctuations or moisture, movements in the soil inevitably occur. But the crux of the matter is that the elongation behaviour is different for every material. Thus, tiles usually react differently to changing conditions than the underlying floor. If there is a rigid connection to the ground, this can quickly have unpleasant consequences. Although the movements are usually only fractions of a millimetre, the resulting stresses are sufficient to cause cracks or fissures in the tiles. Such damage can be prevented with decoupling mats. This is because they provide the necessary scope for the materials to expand independently in all directions.

What is a decoupling mat?

As the name suggests, a decoupling mat decouples the covering from the floor. This means that the mat forms an additional flexible separating layer between tiles and substrate. Since there is no longer a direct connection, movements, tensions or vibrations are no longer transmitted from the substrate to the tiles. The decoupling mat absorbs them completely or at least minimizes them so that no cracks can develop.

Where should a tile decoupling mat be used?

To be on the safe side, there is no harm in principle in laying tiles decoupled. However, in some cases it is particularly important. First and foremost, this concerns the laying of tiles on critical or vibrating surfaces. In other words, wherever the risk of stress-related damage is particularly high or where unevenness and cracks in the substrate have to be compensated.

Freshly laid screed, for example, tends to crack when drying, which can be bridged by a decoupling mat. Decoupling mats are also obligatory when laying tiles on an existing wooden floor. This is because the latter generally reacts to external influences, such as temperature or humidity, with stronger expansion behaviour.

But even if large areas and/or large-format tiles are bonded, above-average stresses can occur overall. The same applies to spot or weather-related temperature fluctuations when tiles are laid, for example, on underfloor heating systems or in outdoor areas. In addition, decoupling mats are also highly recommended for particularly high loads (e.g. in garages) in order to provide the necessary protection against cracks or breakage.

In addition, a decoupling mat improves the adhesion of the tiles, making it possible to lay them on poorly adhering subfloors. For this reason, for example, decoupled installation should also be preferred on floors with existing layers of adhesive, varnish or paint.

ACHTUNG: However, with particularly flexible substrates (e.g. if the rafter spacing in the substructure is too wide), decoupling mats sometimes reach their limits. In this case, it is recommended to first lay plasterboard or OSB boards and only then to attach the decoupling matting.

What types of decoupling mats are available?

Various manufacturers offer decoupling mats in various designs and materials. Most common are products made of plastic, rigid foam or textile fibres, which are usually available as yard ware on rolls in specialist tile shops or DIY stores.

What all commercially available decoupling mats have in principle in common is their multi-layer structure. While the flexible core of the mat ensures the described equalization of tensions and movements, the mostly nubbed outer layer is used for fixing to the substrate on one side and the tile covering on the other side. In addition, ventilation ducts are often installed on the underside, allowing moisture to escape from the respective substrate even after the tiles have been laid.

In principle, modern decoupling systems are therefore suitable for almost any difficult substrate, such as concrete, mixed subfloors, wooden floorboards, chipboard, cement or dry screed, old tiles and many more. Which decoupling mat is best in a specific case, however, depends on the respective area of application and the associated requirements. This is because in addition to the actual function of decoupling, most mats also have other advantages.

Textile mats in particular, such as a PCI decoupling mat, are characterised by improved footfall sound insulation. While other systems, such as Schlüter Ditra decoupling mats, are universally applicable at all, as they combine multifunctional properties in one product with decoupling, sealing, vapour pressure compensation and drainage.

How are decoupling mats installed?

Laying decoupling mats is easier than you might think, but there are a few things to consider.

In principle, decoupling mats can either be glued over the entire surface or laid as a floating installation, whereby the former is more common in practice. However, the method to be used for the respective product always depends on the manufacturer’s recommendations.

Nevertheless, the procedure for both installation techniques is almost identical and essentially consists of the following steps:

Step 1: Prepare the substrate

Regardless of whether the decoupling mat is to be laid floating or glued, the subfloor must be clean, level and load-bearing. For highly absorbent substrates, a primer or a tile primer may also be useful.

Step 2: Measuring and cutting the mats

Before laying, the spatial conditions are measured and the mats are cut to size accordingly. In order to avoid unnecessary waste, special care should be taken – even a laying plan can sometimes be helpful. To avoid sound bridges, insulation strips should also be used in the edge areas.

Step 3: Attach decoupling mat

With floating installation, the decoupling mat is only loosely applied to the substrate. For full-surface bonding, the mat is fixed with highly flexible tile adhesive (marking C2). It should be noted that the adhesive hardens very quickly. Therefore, only as much should be applied as can be covered with the decoupling mat within a few minutes.

Step 4: Sealing the joints

Although decoupling mats are waterproof on the surface, water can still get into the ground at the joints. Therefore, an appropriate sealing of the latter is necessary. Usually sealing tapes are used to prevent the penetration of moisture under the tiles.

Step 5: Laying tiles

The decoupled subfloor is then ready, on which the tiles can be laid in the usual way using flexible tile adhesive.

What does decoupling cost?

Finally, a few words about the costs of decoupling mats:

Basically, of course, the material requirement is decisive due to the number of square meters of the area to be decoupled. In the end, however, the materials used as well as the quality and functionality of the selected mat, but also the manufacturer, are decisive for the actual price. Standard mats are available for just a few euros per square metre, while particularly high-quality products are happy to make a multiple of that. On average, a realistic calculation can be made at around 10 euros per square metre, plus the cost of the flexible tile adhesive. All in all, decoupling mats are therefore not exactly cheap. With regard to a durable and above all damage-free tiled floor, the investment is definitely worthwhile.