Efflorescence
The efflorescence , also known as efflorescence , is one of the structural damage and describes deposits of mostly white powder or crystals from soluble salts on the building surface . If a salt efflorescence is hard and compact, one speaks of a "salt crust". The physical process that leads to efflorescence is called salinization .
causes
Efflorescence generally results from the evaporation of saline pore solutions. The efflorescence salts originate either from the building material, the soil, utility water or the air.
If water is present in a porous structure, existing efflorescence salts are dissolved in the water and transported via the capillary pores to the component surface, where they are deposited when the water evaporates. For this, the evaporation rate must be low, especially less than the capillary suction capacity of the pores. If the evaporation occurs too quickly, the salts are already precipitated in the inner pore space of the component. These precipitations are then not visible from the outside, but can lead to flaking due to the increase in volume. Therefore, in addition to the visual blemish, efflorescence is usually an indication of damaging blowing or blasting effects inside the component. The efflorescence manifests itself in fine crystals, but in rare cases also as floury or glaze-like mass. Sometimes amorphous deposits reach a thickness of a few centimeters. The efflorescence is usually white to off-white, and sometimes yellow or green. Therefore, they are particularly recognizable on dark backgrounds.
The most important building-damaging salts are summarized in the table:
| Salts | Occurrence | |
|---|---|---|
| Carbonates | Calcium | concrete |
| sodium | Natural stone surfaces (treated with water glass) | |
| Chlorides | magnesium | Concrete, use of sea water |
| sodium | De-icing salts, freeze additives | |
| Nitrates | Calcium | Toilet facilities, stables, urea as a grit |
| magnesium | ||
| Sulfates | Calcium | Concrete, plaster, brick and natural stone masonry, roof tiles |
| magnesium | Natural stone, dolomitic limestone | |
| sodium | Brick and natural stone | |
Nitrates are mainly found in agriculture, e.g. B. in stables , leaky toilet facilities and animal excrement. They arise from the microbial conversion of protein degradation products ( liquid manure ).
When calcium nitrate, also known as wall nitrate, is formed, the lime is removed from the mortar and converted into further calcium nitrate. When the weather changes, there are alternating dissolution and crystallization processes that can wear down the mortar and stone over time and thus destabilize the masonry.
Modern salt sources are:
- building materials containing cement , trass and silicate
- many injection materials
- Remedies against dry rot or mold
- Carbonate-Silicate Cycle and Silicate Weathering
- Blowing reactions of electrogypsum with cement mortar
De-icing salts dissolved in spray water can also cause efflorescence.
Protective measures
In order to permanently prevent efflorescence, the moisture penetration of sensitive building materials must be prevented. For this purpose, the wall can be actively drained and the adjacent sewers and excavations can be drained to prevent unintentional backwater. If the masonry has already been damaged, it must be pried out and replaced. Efflorescence should generally be brushed off dry, because with wet treatment the salts dissolve in the water and are largely absorbed again by the masonry. Then the affected component can be acidified with approx. 5 percent acetic acid or hydrochloric acid diluted with water.
There are various techniques for desalination of the masonry:
- Washout technique
- Compress technique or sacrificial cleaning technique (with salt-absorbing compresses, is removed again after enrichment with salt)
- electrophysical methods
With the help of impregnating agents, the pores can be closed and moisture penetration is prevented, but further salts are introduced into the building structure. Another protective measure is water repellency . These are active ingredients that cover the inner pore and capillary surfaces and thus make them water-repellent (hydrophobic). Since the pores and capillaries are not closed by this, the diffusibility (vapor permeability) of the building material remains almost unchanged.
Restoration plasters are often also applied after the old plaster has been removed. An important measure nowadays to prevent moisture and salt damage is the installation of horizontal barriers that prevent rising soil moisture from getting into the masonry.
See also
literature
- Frey, August, Günter: Construction technology - specialist knowledge of construction . 10th edition. Europa Lehrmittelverlag, 2003, ISBN 3-8085-4460-0
Web links
- Moisture and salt in old buildings - collection of facts and tips 1 and moisture and salt in old buildings - collection of facts and tips 2 . konrad-fischer-info.de
Individual evidence
- ↑ efflorescence in Duden (at duden.de); Accessed July 5, 2018.
- ↑ Information from RWTH Aachen University on types of damage to natural stone surfaces (PDF, 1 MB); see under "Group 2 of weathering forms"
- ↑ Salt efflorescence . In: Angela Weyer et al. (Ed.): EwaGlos. European Illustrated Glossary Of Conservation Terms For Wall Paintings And Architectural Surfaces . English Definitions with translations into Bulgarian, Croatian, French, German, Hungarian, Italian, Polish, Romanian, Spanish and Turkish. Michael Imhof, Petersberg 2015, ISBN 978-3-7319-0260-7 , p. 226 , doi : 10.5165 / hawk-hhg / 233 ( hawk-hhg.de ).
- ↑ Rising wall moisture + building drainage 6: wall moisture, horizontal sealing masonry, masonry salinization + building drainage , at konrad-fischer-info.de
- ↑ Rising wall moisture + building drainage 6: wall moisture, horizontal sealing masonry, masonry salinization + building drainage , at konrad-fischer-info.de