Restoration Plasters In The Old Building

When renovating old buildings, there are a number of points to consider, especially in the case of moisture and salt damage.

A basic analysis is a basic requirement for professional measures and the right choice of materials. In recent years, the renovation of old buildings has become the mainstay of their company for many companies. Before renovating an object, you should first take a closer look at the foundations and basement rooms, as penetrating moisture can gnaw at the building structure. Rising masonry moisture is mostly due to a missing or defective horizontal insulation and moisture present on the masonry. The damage to the paint, plaster and masonry is mainly caused by the crystallization pressures that occur in the floor salts that are also transported or by the effects of moisture on the wet plaster.

The type of salts present is important for the damage mechanism and must therefore be determined. In the case of larger properties, such investigations are carried out by special renovation planners and expert reports are drawn up. For normal properties, plaster manufacturers usually offer this at cost price. The examination, which is an imperative measure to be carried out in accordance with WTA leaflet 2-9-04 "Restoration plastering systems", is the basis for professional restoration and material selection. After the analysis is available and after the investigations on the property, the scope of the renovation is determined. These include, for example, the amount of plaster renovation taking optical aspects into account or the recommendations for accompanying measures such as horizontal and vertical insulation.

The use of renovation plasters is a relatively inexpensive way to keep the plaster surface optically intact for many years. Both the old plaster standard DIN 18550 and the new DIN V 18550 refer to the special renovation plasters WTA, since conventional plasters are not suitable for renovation cases in buildings with saline masonry. The durability of a renovation plaster in combination with a subsequent horizontal insulation is approximately the lifespan of a plaster on normal, dry masonry. Renovation plaster used as the sole measure will last about ten times longer than conventional plaster.

Of course, renovation plasters also have their limits in terms of applicability, such as with pressurized water, which can overcome water repellency and penetrate the highly porous plaster. Restoration plasters enable optically dry wall surfaces, but the moisture is released into the room in vapor form. If ventilation is not carried out, condensation can lead to a high level of moisture, which in turn creates the possibility of mold problems.

facade

Restoration plasters are of course also used outdoors. The aforementioned high porosity is the reason why these plasters can only be used from the top of the site. Dense materials such as cement plasters with sealing slurries or bituminous seals are suitable for the areas below. Since this reduces the proportion of the "absorbent" surface, less moisture gets into the building and thus supports drying. The transition in the base must also be sealed up to a height of approximately five centimeters.

If you find salted plinth surfaces, the other facade surfaces are often more damaged and need to be revised. At the beginning it has to be checked whether the necessary load-bearing capacity of the old plaster or old coat is given, which enables a revision. If there are already any uncertainties, it can be clarified in advance whether a complete removal of the inventory is cheaper.

It is important whether the old plaster still adheres to the surface and whether cavities have formed. These can be easily tapped gently. B. localize with a hammer. Hollow spaces with little expansion (up to palm-sized areas) can be left. Larger areas have to be cut off and repaired. If the old plaster is very hard and cavities have formed, trying to repair it can result in the plaster completely detaching from the surface. In this case, the inspection measures must be agreed with the client and planner beforehand.

Coatings can be tested with a cross cut, abrasion test in a moist and dry state or a tear test with an adhesive tape. But the safest thing is always a tear test, in which a surface of at least 0.5 square meters is coated with a coated adhesive plaster, in which a fabric is inserted. After a standing time of approx. One week, when the fabric is torn out, it can be clearly seen whether the old plaster and paint are sustainable.

If this is the case, care must be taken to ensure that there are no building-damaging substances in or on the facade. On the one hand, there are the salts that have been introduced by rising masonry moisture. Since the surfaces are usually directly connected to the salinization in the plinth area, the renovation plastering work must be shifted upwards accordingly.

Blocking reasons seal the facade surface, which can result in backwetting, which can result in frost damage. In this case it is better to remove the old plaster in the corresponding areas. Removal of biological infestation is also necessary to prevent an early resettlement by existing spores.

Cracks are caused by movements in the plaster or in the plaster base. The right measures can only be taken if the cause of the crack is known. It is also important whether there are still movements of the crack flanks in relation to one another and to what extent they take place.

The WTA leaflet E-2-04-07 / D "Assessment and repair of cracked plasters on facades" presents possibilities for revision. The methods mentioned here are partly controversial, but give a good overview of the different types of crack repair.

Outside, one can assume that there is always a change in crack width due to changes in heat and humidity. An almost classic method is the revision with a fabric filler. Thanks to the inserted reinforcement, the forces are distributed over a large area and prevent wide, physically problematic cracks.

However, if the old plaster is still largely intact and the cracks that have occurred are not too wide, a plaster overhaul can also be avoided. When it comes to crack repairs, you can choose between purely filling and bridging systems. Purely mineral coatings are always only filling, but can be made more elastic by adding organic binders. Organic paints may have a very high elongation, which, depending on the material, have high crack-bridging properties. Unfortunately, the water vapor permeability decreases with these coats of paint, so that detachments are possible due to the accumulation of moisture behind the coat.

The renovation of buildings is an interesting, if sometimes delicate, topic. Until some of the walls are open, nobody knows what work and difficulties await you. Since the problems with older buildings are so complex, the trades should coordinate with each other right from the start so that an acceptable result can be achieved for all specialist companies involved. r supplement with a suitable humidity measuring device and temperature, air humidity and dew point measuring device.

If such repaired plaster surfaces appear, the surface should be homogenized by means of a full-surface filler in order to prevent cracking in the finished top plaster.

Olaf Janotte, application technology BaumitBayosan

Source: Malerblatt 08/2008