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(This page was automatically translated from German. Kapillarität)

What is capillarity?

Capillarity one determined how fast a component how much water absorbs when itdirectly into contact with moisture, (rain, splashing in the kitchen and bathroom, soil moisture, condensation), the other determines the drying speed of new or renovated or parts of walls, where diffusion transported by water vapor to water condensed.
A useful measure of the capillarity of building materials is the water absorption coefficient (w) [The water absorption ratio indicates how much water the substance within a certain time record.] It indicates how much water is measured in kilograms by the square meter moistened area a certain time -- For example, in one second or one hour - the completely dry material penetrates. For many materials with a little water absorption coefficient, only low-trained capillarity, is a particularly high "water absorption" characteristic.

Capillary When a large amount of water transported. However, it is in water vapour diffusion much less.

Well-trained capillary capillaries with different diameter:
Large water absorption capacity, high humidity tax assets, for example, bricks, gypsum

Closed cell-structure with few capillaries between cells:
Large water absorption capacity, low humidity tax assets, for example gas concrete

Structure with small, closed pores and capillaries: Low water absorption capacity, low humidity tax assets, for example heavy concrete, concrete leca
Capillary structures in the stonework

Materials with strong capillarity transports moistened per square meter area in the first hour and 20 liters of slightly more (per wet the material is, the less water it takes additional). In materials with strong capillarity liquid water is transported as far, in a material each of the damper to the drier regions. In components made of layers of different structure the capillary the water migrates in the direction of the layer with the finer capillaries (or with the higher water absorption coefficient); layers with coarser or more imperfect capillaries and smaller values for w) are almost sucked drily.

Capillary of water against water vapor diffusion of power is often the case in winter, even the rule. When a building materials with high levels of water vapour capillarity to condense, begins at the same time the transport of condensation in the direction of the material lower humidity, so the warmer side of the wall where the condensation to evaporate again. In such films, there is often no soaking through condensations when they constructed might be expected. The capillary effect in the vertical transport also against gravity - not theoretically unlimited, in practice we can gravity but negligible. In this way old buildings also remain in the cellar walls sufficiently dry, that not against moisture from the ground was closed off.

One must in no way hinder the Capillary. In the basement by a tight fitting inner moisture barrier (see here under steam brake) or in the wall surface area when finished in the base area to protect against the rain hindering water, water repellent (hydrophobic) or even water-resistant coating. Before the coating must then begin foundation and basement walls against intruding against moisture from the ground off.
This is particularly critical at a house renovation, when the wet brick base with disguises or closing a densely cement plaster applied. The moisture then rises up and can then only in height of the ground floor window to escape, both internally and externally.

When drying out of baufrischen walls, floors or ceilings, the excess moisture initially only by Capillary component to the surface, where it evaporates.Poren und Kapillare im Mauerwerk, Wechselwirkung zwischen Kapillare und Diffusion If not all material pores filled with water, start the water threads in the capillaries to break, slowing the drying and gradually, the vapour diffusion, until the part has its practical humidity has reached (see contribution Wall moisture Table 1). This is the moisture content, in any structure more than remaining intact. Depending on the part thickness, initial humidity, tanning, ventilation and other external influences, it takes several months to several years.

The longest it takes for materials with low-trained capillarity saturation and a high water content. The fastest is what building materials with high capillarity, such as full bricks. You have at medium gross densitys water absorption coefficient by 20-30 kg / (m2h 0,5) compared with lime sandstone with 10 and porous 4-8 and synthetic resin plaster on 1. Further values under building materials catalog.

The downside of this desirable feature is that such tiles also chemically aggressive rainfall faster and further into the transport component as materials with lower capillarity. Very much better than full-brick behave hole tiles. With them is the effective Capillary plane through the hole shrinks. Hollow brick or high-hole outside bricks are therefore sight facades particularly well suited. The best protection of components made of materials with high water absorption capacity are ventilated panels (wood, slate) or facade greening. (See earlier contribution to the facade greening.)

Capillarity physical explanation and computing example.

Quelle:Eichler, Friedrich; Arndt, Horst; Bautechnischer Wärme- und Feuchtigkeitsschutz 1989; Bauverlag
Kur, Friedrich; Wohngifte, Handbuch für gesundes Bauen und Einrichtungen, 3. Aufl. Verlag Eichborn, 1993, S. 545

Ingenieurbuero Peter Rauch

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