Capillary breaking layer
A layer of crushed stone below the foundation level or the floor of a building is called a capillary-breaking layer or roller , which, like a horizontal barrier, interrupts the capillary transmission of soil moisture or groundwater (see also: Rising moisture ). In road and path construction, the capillary-breaking layer is called the frost protection layer .
Alternatively, many other materials are also suitable for protecting against soil moisture by interrupting the capillarity. However, these are usually referred to as sealing membrane , drainage or insulation layer according to their primary function .
Before the introduction of the modern types of building waterproofing according to DIN 18195 , such as the black and white tub , capillary-breaking layers were used to reduce moisture penetration in basement rooms and floors in contact with the ground.
In the case of foundations at a depth of up to about 1 meter, the ballast layer also served as a drainage under the foundations and floor slabs, in order to avoid the accumulation of water directly below the foundation of the structure, which can lead to settlement and material damage, in particular due to alternation of frost and thaw .
Traditionally, a capillary-breaking layer is formed by a layer of at least 15 cm (sometimes up to 60 cm) thick of non-cohesive aggregate such as coarse gravel with a grain size of 16/32 mm (diameter of the smallest / largest grain from the grain distribution line ). In general, a rolling (non-cohesive), easily compactable, frost-resistant and relatively unyielding mineral mixture with a grain size of 0/45 mm (e.g. soil group: GW, multi-layered gravel) can be used. Avoid fine or dirty gravel. If the subsoil is very damp, a layer of dust on the gravel can allow the moisture to rise by capillary action .
The type and expense of the sealing measures depends on the type of soil , the highest groundwater level and the intended use of the space. In the case of higher demands on the dryness of the cellar or floor, a horizontal seal in accordance with the former DIN 18195 or DIN 18533 for surfaces in contact with the ground must be arranged.
Before concreting a blinding layer , a floor slab or a foundation, a PE film or a fleece is often laid on the capillary-breaking layer to prevent the concrete from running into the gravel. It is often advisable to lay a separating fleece between the existing subsurface and the rolling or base layer in order to prevent "mixing processes" or uneven base layer thicknesses caused by sagging in the case of flexible subsoil (such as silt, clay).
If thermal insulation is provided under the floor slab, foam glass gravel can be used instead of gravel to produce a capillary-breaking layer that also has good insulating properties. Foam glass gravel does not allow capillary moisture transport.
literature
- K. Lufsky, M. Bonk, E. Cziesielski: structural waterproofing , BG Teubner Verlag, 2001, ISBN 3-519-35226-5
