Minimum thickness for the screed

The thickness of a screed layer depends on the type of construction used as well as on the required load-bearing capacity; in addition, the structural conditions also play a role in some cases. The grain sizes of the aggregate also play a role in some types of construction. Much of this is also a matter of experience.

Irrespective of this, however, DIN 18560 also specifies so-called minimum nominal thicknesses for the individual construction types. This minimum thickness is normalized and must not be undercut in the respective construction method, with higher surface loads than usual, the DIN also requires a corresponding increase in screed thickness.

Compressive strength and bending tensile strength

The DIN regulates the installation thicknesses of the screed fundamentally according to compressive strength and bending tensile strength, but normatively, the hardness classes specified in DIN 13813 are used here. They apply to vertically occurring loads of less than 2 kN per square meter.

The minimum nominal thicknesses for floating screeds and heated screeds

Floating screeds and heated screeds, as they are common in the living area, must have the following minimum thicknesses according to DIN 18560:

Calcium sulphate flowing screed must be at least 35 mm thick in the hardness class F4, in the hardness classes from F5 a screed minimum thickness of 30 mm is sufficient. In contrast, calcium sulfate screed must be at least 45 mm thick in the F4 grade, 35 mm in the F5 class and 35 mm in the F7 class. Cast Asphalestrich in hardness class IC10 must be at least 25 mm thick. For cement screed, hardness of F4 is 45 mm thick as a minimum nominal thickness, in class F5 it must be at least 40 mm.

However, it is also important to note the required coverage height of the heating pipes for underfloor heating, where the pipes are located in the screed. Here the minimum nominal thickness is exceeded. For calcium sulphate and cement screeds, a minimum covering of the tubes of 45 mm in hardness class F4 applies, in higher hardness classes also 30 mm are permissible. For mastic asphalt screeds, the minimum pipe coverage height is 25 mm, but here only strength class IC10 is permitted.

Nominal thicknesses for compound and sliding screeds

When composite screed there is no minimum but a maximum thickness in the DIN, namely 50 mm, mastic asphalt screeds may be at most 40 mm thick. In the case of screeds on separating layer, on the other hand, there is a minimum height, namely 30 mm for calcium sulphate screeds, 45 mm for cement screeds and 25 mm for mastic asphalt screeds.

Video Board: Sand Cement Screed Thickness Minimum?