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Crack Repair

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Crack Repair
Crack Repair

Video: Crack Repair

Video: Crack Repair
Video: How to repair, seal and waterproof large cracks in concrete, cement, steel, pvc 2023, November

Cracks are an ongoing issue. Again and again there are misunderstandings and disputes between the contracting parties.

The following small overview is intended to encourage you to find a solution more quickly and more specifically to crack problems.

Already in the planning phase of a crack repair, attention should be paid to the causes of damage in order to avoid later misunderstandings in the execution. Unfortunately, the building owner's wish to obtain a visually appealing and crack-free plaster surface and the increasingly shorter execution times do not leave enough time to find out the actual causes. The fact that a completely crack-free execution is generally not possible with manual work is often not accepted on the part of the building owners and clients.

Individual small cracks (hairline cracks) are, however, permitted to a limited extent if they do not impair the visual or technical value of a plastered surface. The visual value of a facade or interior surface is only impaired if the cracks become disruptive when viewed at a customary distance and viewing position and the plaster surface has a special design or representative meaning. On the other hand, if the crack pattern affects the protection against driving rain of the masonry, the plaster and the paint, there is a technical defect.

Assessment and assessment

For the assessment and assessment of facades or plastered surfaces in the interior, cavities and cracks with their crack widths should be documented. Often a photo is enough to show the damage. With a crack comparison scale, determining the crack width on site is not a problem. Cavities are to be located by tapping the surfaces. If you compare the crack patterns, including the additional information - with the crack patterns documented in the standardization and information sheets - the cause of the crack can often be narrowed down and determined. The following sketches show some typical crack options.

The WTA leaflet (2–4 edition: 8.2008 / D, assessment and repair of cracked plasters on facades) contains helpful information on how to determine the causes and assess whether cracks that have occurred are a technical or visual defect, such as the substrate to be checked before a repair and which repair system to choose (tables can be downloaded from the Malerblatt homepage at). The WTA leaflet provides information on the typical crack characteristics. It also explains procedures for repairing individual cracks (procedure E) and procedures for area repairs (procedure F). With the help of tables, a suitable method can be selected for the essential characteristics of the damaged areas listed above.

The use of crack-bridging or crack-filling coating systems has resulted, among other things, in re-wetting and damage to the plasters in the crack area and beyond, which is why the applicability of the various systems has been made dependent on the material properties of the coatings.

Flat renovation processes are used for high technical and optical requirements as well as for high weather conditions. In this way, a large number of cracks and further cracks to be expected can be covered.

With a crack comparison rod, determining the crack width on site is no problem.

Typical crack options

Possible causes of cracks caused by the plaster:

  1. improper mortaring, poor mortar
  2. low overlap, joint on joint
  3. unsuitable roller shutter box, too different plaster substrates

Possible causes of cracks in the building:

  1. Change in shape of the ceiling
  2. Shrinkage of the masonry
  3. Change in shape of the masonry
  4. different load transfer / notch tension
  5. Action from the roof structure, weakened masonry

Cracks due to plastering:

  1. Shrinkage cracks
  2. Bag cracks
  3. Stress cracks

Different systems

The repair procedures differentiate between mineral and organically bound systems, which have to be selected depending on the plaster (type of binder and strength).

For this reason, procedures F1 to F3 in the table should be considered. Crack-bridging organic coating systems (F1) are often very vapor-tight, ie they have a high diffusion resistance to water vapor or carbon dioxide. This makes these coatings unsuitable for lime-rich plasters of strength classes CS I and CS II. Furthermore, no backwetting may occur - even on a sufficiently solid surface (from CS III), as otherwise damage can result. Newer systems, which despite their good elasticity also have good vapor permeability, should be preferred.

The process F5 "mineral reinforcement plaster and mineral finishing plaster" has proven itself very well in the past years and is seen as twice as efficient compared to the previous statements. Therefore, today it can be used as safe crack bridging of cracks with crack width changes of approx. ± 0.2 mm. At the same time, it is suitable for the revision of stable, also lime-rich (CS II) old plasters. Organic finishing plasters are possible with a sufficiently solid surface (at least CS III), however, the statements of the manufacturer must be observed, as there may be exceptions in isolated cases. This method has also proven particularly useful for reworking facades with stone-plaster cracks.

Research into causes

In order to be able to determine a suitable measure for the renovation of a cracked facade, knowledge of the crack characteristics and the causes that can be derived from them is essential. The mentioned characteristics of the different crack shapes are relatively easy to recognize in practice. If the crack patterns are not so easy to classify on site or if very large crack widths occur, then the causes of the crack should be determined and evaluated with more effort, possibly also by an expert. Last but not least, the technical departments of the manufacturers concerned can of course also be consulted.

Further help for masonry renovation include:

  • BFS - Leaflet No. 19 "Cracks in external plasters - coating and reinforcement" and No. 19.1 "Cracks in unplastered and plastered masonry, in plasterboard and similar materials on substructures - causes and processing options" Publisher: Federal Committee on Color and Property Protection eV
  • Information Edelputz No. 20 "Repair and modernization of facades with mineral noble plasters" Publisher: Federal Association of the German Mortar Industry eV
  • WTA leaflet 4–5–99 / D, assessment of masonry - masonry diagnostics

Stefan Walla, Baumit

Images: Baumit Source: Malerblatt 09/2013