How is concrete damaged by salt?

Baunetz_Knowledge

If the masonry is also too salty, the salt dissolves in the water and migrates to outer or higher zones with lower humidity, where good crystallization conditions exist. The pores in the masonry are narrowed further by the salt crystals and prevent drying out. The increase in volume of the salt crystals damages plasters and paints. When the plaster is destroyed and fallen off, this process continues in the outer wall zones. Frost in winter also damages the masonry from the frozen moisture.

Remedial measures
To create a renovation concept, it must be checked what the causes of the moisture damage and the salts in the masonry are. The leaflet on renovation plaster systems 2-9-04 / D of the Scientific-Technical Working Group for Building Conservation and Monument Preservation (WTA) offers solid support. The leaflet explains the principles of action, sets up test criteria for restoration plasters, defines restoration plaster systems and their processing, and provides support in planning. If, for example, there is rising damp, a horizontal seal must also be installed or additional drying measures must be taken. The degree of salinization should be analyzed in order to be able to choose the appropriate plaster system. In addition, damaged old plaster should - of course - be removed over a large area before restoration plaster is applied.

Restoration plasters
Restoration plaster systems may not be used below the top of the site; other suitable sealing measures must be taken here.

Restoration plasters have a light, pore-rich structure with high water vapor permeability to allow the existing moisture to dry out. The water vapor exchange takes place via coarse, non-capillary pores that cannot pass on water and / or salt solutions. Salt crystals can become lodged in sufficiently large pores, but they cannot block or prevent dehydration there. Due to their hydrophobicity, fine capillary pores hinder the absorption of moisture from the outside and at the same time the forwarding of water or salt solutions. This means that no moisture concentrations and no frost damage can occur on the outside of the plaster. The salts are not neutralized in the masonry but are stored harmlessly. The system structure depends on the existing damage and is also regulated in WTA leaflet 2-9-04 / D based on the degree of salinization.

execution
During the execution, the system structure, the suitable plaster, the skilled craftsmanship and the consideration of the climatic boundary conditions are directly important for the success of the renovation measure.

Expertise on the subject

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Planning aids

WTA leaflets

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