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When renovating masonry damaged by moisture and salt, various criteria must be observed in order to then take the necessary measures. Who really strives for permanent improvement should not rely solely on the renovation plaster. Olaf Janotte Deputy Head of Application Technology Baumit Sanierputz-WTA is a tried and tested material that has been tried and tested according to all the rules of art. But no matter how good it is, it remains only a stone in the mosaic of renovation work with masonry damaged by moisture and salt. Who really strives for permanent improvement should not rely solely on the renovation plaster. It may be that the material remains as the only variant after all preliminary examinations and cost-benefit considerations have been completed. If so,this result should not have been made simply out of convenience, but out of technical expertise. Rising masonry moisture is due to a missing or defective horizontal insulation in combination with moisture present on the masonry. The cause of the damage is the capillary water absorption, through which the water is “sucked up” like through small straws. This mechanism is reinforced by pressing seepage or slope water. If salts have reached the masonry with the water from the floor, they also have the option of attracting moisture from the air and also depositing it in the masonry. The damage to paint,Plaster and masonry are essentially caused by the crystallization pressures that occur in the soil salts that are also transported or by the effects of frost. Examination methods Due to the now lower costs for electronic measuring devices, you can get a good overview of the moisture balance and determine the amount of renovation plaster processing without the help of others. You should not only pay attention to the moisture marks on the plaster surface. If you are undecided, only a salt test in the laboratory can provide meaningful values. Since salts (usually only differentiated according to the groups chlorides, sulfates and nitrates) are important for the damage mechanism and the renovation plaster processing, knowledge of the type and amount is absolutely necessary. Expert,but renovation plaster manufacturers also offer such tests for salinity and moisture. Condensate can also lead to moisture damage, which can be interpreted as rising masonry moisture. However, since mostly only the surface is damp, a moisture analysis in the masonry and a temperature measurement on the surface can provide clarity about the cause relatively quickly. Sealing measures Lasting renovation can only be achieved if further transport of moisture and salts into the masonry is prevented. If the question now arises whether horizontal insulation is necessary or not, simple moisture measurements are not sufficient. For larger objects, such examinations are carried out by special specialist planners. Subsequent horizontal insulation is often ruled out for financial reasons. In order to reduce the moisture input, at least an intact vertical seal should be aimed for, as can be achieved with barrier plasters, mineral sealing slurries, bituminous paints or waterproof welding sheets. Restoration plaster-WTA Restoration plasters-WTA are regulated by WTA leaflet 2-9-04 / D, restoration plastering systems. The renovation plaster area is to be laid up to about one meter above the old salt or moisture zone. The masonry must be cleaned after the old plaster has been knocked off. The subsequent spray is to be coordinated with the renovation plaster system. Even a leveling plaster must match the renovation system in terms of its physical properties. Its use makes sense for larger objects. In the case of smaller areas, compensation is carried out with renovation plaster WTA so that no additional material change is necessary. If the total thickness of the renovation plaster system exceeds four centimeters in the area, a pore base plaster must be used as a plaster. Today, renovation plaster WTA is largely processed with the plastering machine, but they can also be mixed by hand. Mixing in (mixing too little) leads to an insufficient pore content, which jeopardizes the function of the renovation plaster (drying, salt storage). Overmixing the renovation plaster (preferably when mixing by hand) leads to a very high pore content, which results in a considerable drop in strength. Depending on the degree of salinity and the type of salt, renovation plaster WTA is carried out in thicknesses of at least 10 or 15 millimeters per layer. If the layer is too thin,strong sunshine and / or stronger wind, the binders can "die of thirst", ie the binder does not get the amount of water necessary for complete setting. This leads to a sharp drop in strength. Basically, the entire renovation plaster layer must be at least two centimeters thick at all points (three centimeters in the case of heavy salinization) in order to reliably prevent salt and moisture breakdown. Mostly, the application will be done in two or more layers due to the uneven surfaces, whereby the last layer is processed as a finishing layer. The lower layer must be roughened well to ensure mechanical anchoring. Standing times of 1 day / mm of plaster thickness must be observed. Special renovation plasters can also be applied in one layer. Since there are some significant differences here,should always be checked with the respective material manufacturer. In order to be able to cure safely, renovation plasters require a minimum layer thickness of one centimeter per layer, according to the WTA leaflet "Renovation plaster systems". This means that some structures cannot be produced with these plasters (trowel, grooved plaster, etc.). In this case, their water vapor permeable structure makes mineral plaster a safe alternative that can be applied to the renovation plaster. If the desired surface structure can be achieved with the renovation plaster, the question is which paint should be used. With pure silicate paints, a pretreatment with an etching liquid is necessary to break the water repellency on the surface so that the paint adheres well. Etching the substrate can be omitted with dispersion silicate paints, since the adhesion is achieved by adding a dispersion. High-quality silicone resin coatings are also a good alternative. Adequate vapor permeability must be guaranteed for all coatings on renovation plaster. As a requirement, an sd value of <0.2 m for each individual layer must be observed. In the outdoor area, the paint must also be water-repellent. The renovation of damp and salt-damaged masonry, both outside and inside, is now reliable and possible with a high degree of security through the use of renovation plaster WTA. Adequate vapor permeability must be guaranteed for all coatings on renovation plaster. As a requirement, an sd value of <0.2 m for each individual layer must be observed. In the outdoor area, the paint must also be water-repellent. The renovation of damp and salt-damaged masonry, both outside and inside, is now reliable and possible with a high degree of security through the use of renovation plaster WTA. Adequate vapor permeability must be guaranteed for all coatings on renovation plaster. As a requirement, an sd value of <0.2 m for each individual layer must be observed. In the outdoor area, the paint must also be water-repellent. The renovation of damp and salt-damaged masonry, both outside and inside, is now reliable and possible with a high degree of security through the use of renovation plaster WTA.
Further information on renovation plasters is available from: Baumit GmbH Reckenberg 12 87541 Bad Hindelang Tel.: (08324) 921-0 / Fax: 1029 www.baumit.de