Renovate external plaster or repair it only partially

After many years or decades, an external plaster can be quite battered and have concrete damage. When renovating, the old building skin does not necessarily have to be "pulled off". The necessary measures are composed of background conditions, load situation and damage pattern.

Damage analysis and cause evaluation

Between repairs and a refurbishment, there are many gradations to bring an old plaster back on its feet. When the plaster crumbles, cracks or moisture builds up, the causes influence the effort and the degree of intervention.

Several indicators should be evaluated individually:

  • If the exterior plaster crumbles, moisture or cracks are the cause. If so,
  • Where does moisture and cracks come from? Does incident precipitation from the outside cause damage or masonry moisture? Are the cracks limited to the plaster or do they extend into the masonry and possibly into the joints?
  • Are there larger contiguous surfaces where the plaster separates from the wall?

Check condition of plaster and substrate

The first part of the condition analysis is the assessment of the substrate and the adhesion of the plaster. Typical test steps are:

  • Strength of the plaster, which is determined by scratching
  • Suction behavior of the plaster and the substrate by means of selective moistening
  • Localization of cavities by acoustic knock test
  • Adhesive strength of the plaster layers to each other and to the substrate by taking a drill sample
  • Test tensile and tensile strength by applying and removing a covered tissue filling
  • Burning test for the determination of the inorganic and organic layer constituents
  • Durability of the top coat or the visible coating by diamond cuts

Classify damage in the plaster

If cracks need to be repaired, the test with a plaster mark is recommended. The gypsum placed in the crack is observed for about two to four weeks. If the plaster breaks, it is a dynamic crack, the cause of which, like masonry movements, has to be eliminated. In a static static crack a partial repair is sufficient.

Indications that the plaster does not hold may indicate an unsuitable composition or type of plaster. In this case, when renovating the old plaster must be almost completely milled from the ground.

Tips & Tricks

Everything that keeps the old plaster, you can leave on the facade or wall. It is important for every renovation of a well-preserved exterior plaster, not to change the physical function. Pay attention to diffusion and tightness.

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Video Board: How to Patch and Plaster Walls in Your Old House