In exterior plaster cracks do not always represent a defect

When cracks develop in the exterior plaster, in many cases differing opinions arise regarding the scope of the defect and the need for refurbishment. The ratings have a variety of interpretable variables. Origin, development time, size and optical impairment lead to rules of thumb, which are heard in the case-by-case examination.

General and specific evaluation criteria

So-called hairline cracks in exterior plaster occur almost on every building. The corresponding regulations and standards do not specify fixed values ​​in absolute terms. In general, a crack width of up to 0.2 millimeters is defined as hairline crack. Regarding the functional effects, not only the width can be judged. The depth of the cracks and their possible magnification over time are other crucial parameters to define as deficiency or not.

A final assessment of a crack and the need to repair the exterior plaster is composed of functional and optical aspects.

Functionally, note:

  • Whether the façade and building side are affected by more frequent driving rain
  • Whether there is an intermediate layer (styrofoam) between masonry and plaster
  • Whether the crack is just an initial stage or growing

As visual assessment criteria flow:

  • How many cracks have occurred
  • Where the cracks form
  • How well visible the cracks are
  • Whether deposits and soiling increase visibility
  • How strongly the cracks intervene in the visual appearance of the surfaces

Visibility and visualization

Juridically controversial hairline cracks in the outer plaster with relatively stretchable practical properties are interpreted after "common sense". As rules of thumb and guide values, the following criteria have spread:

  • A crack representing a defect must be clearly visible from three meters of viewing distance
  • Visualization by wetting does not support defect assessment
  • Visualization by disproportionate means such as ladders and optical magnifying aids do not support fault assessment

With crack widths over three millimeters, a defect can almost always be claimed. From this width, repairing must prevent functional damage, such as crumbling the plaster and excessive moisture exposure of the façade and masonry. Without proper repair and renovation, considerable consequential damage must be assumed.

Tips & Tricks

Definitions, interpretations and regulations on cracks in exterior plaster can be found in the standards EN 18550, EN 13914, EN 13499 and EN 13500. The Civil Code defines the term "defect" in paragraphs 434 and 633.

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