Anhydrite screed in the bathroom - is that even possible?

Even laying tiles on an anhydrite screed is not without its problems. In addition, there is a warning not to use anhydrite screed as a substrate for damp rooms. Whether you can still install anhydrite screed in the bathroom, and what you have to pay attention to, read in our post.

Anhydrite screed and tiles

Laying tiles on an anhydrite screed is not without its problems. Much has to be considered, and also the preparation of the substrate and above all the subsequent sealing must be carried out with great care.

Otherwise there is a risk of damage to the subsurface, which later necessitates a total refurbishment, or even damage to the screed, whose repair is then even more costly.

Anhydrite screed and moisture

The anhydrite screed, or calcium sulfate screed, consists, as the name suggests, of a high proportion of gypsum (calcium sulfate). Gypsum is very sensitive to moisture, starts to swell and expands.

Anhydrite screed must therefore never come into contact with moisture. If that happens, a high and very costly damage can be the result.

Permissible load classes of anhydrite screed

If you look in the DIN 18560, very clear application areas are defined for anhydrite screed.

The calcium sulphate screed must not be exposed to permanent moisture stress. Wherever moisture can occur, you must protect the screed accordingly - for example with waterproofing and a vapor barrier.

According to the DIN, the installation of calcium sulphate screeds is only admissible where a low level of moisture is to be expected (load class A0). These are also Baths in private homes, provided they have no floor drain. In such a case, the seal must necessarily be a so-called composite seal; in addition, joint sealing tapes must be installed everywhere.

Ground level shower

In the event that a floor-level shower would be installed, the installation requirements are no longer given, since it is in this case a higher moisture stress class than A0. In this case, the humidity stress would be class A01.

So should such installations (as well as a floor drain in the bathroom) be planned, is an anhydrite screed is not allowed, It must then be used another suitable type of screed for the bathroom.

Tips & Tricks

Even with careful execution, errors can occur, which may then be remembered much later. Anhydrite screed in the bathroom is always a risk that should be avoided. Cement screed is certainly always the better solution, so you are definitely on the safe side.

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