Repair cracks in the exterior plaster

In most cases, cracks in the exterior of a building are completely normal and age-related. After all, the plaster is exposed to the stresses of the weather on a daily basis. Of course it wears out. Such a plaster crack must be closed again in order to avoid damage to the building structure. However, if the crack goes deeper, it can be an indication of much larger problems in the building.

preliminary examination

Before homeowners attempt to repair cracks in plaster, it is a good idea to determine what type of crack it is. A precise damage analysis should therefore be carried out. Basically, two types of cracks can be distinguished. On the one hand there are the plaster-related cracks. In most cases they are superficial and actually only affect the plaster itself.

Repairing is relatively easy here and requires neither special expertise nor great manual dexterity. The situation is different with the so-called dynamic cracks. They go much deeper and usually affect not only the plaster, but also the underlying masonry. A dynamic crack is usually a clear indication of defects in the structure - and these defects can be very dangerous.

detect crack type

It should have become clear by now that it is crucial to recognize the type of crack that is visible in the exterior plaster. Luckily, there are a few relatively unique characteristics that help tell them apart.

Plaster crack:

• only superficial, not deep
• only the plaster affected
• the masonry is not affected
• usually occurs over a large area as a combination of network tears
• sometimes poorly visible

dynamic crack

• clear, relatively wide crack
• often reaching up to the masonry
• Plaster elements break easily
• often found near wall breaches

Repair plaster cracks

Fixing a plaster crack is no big deal. Depending on the type and size of the crack or of the cracks, two methods are possible. Method 1 consists of covering the crack over a large area. There are special materials for this, which are available in every hardware store. This variant is particularly suitable for particularly fine plaster cracks, which can often also be found in a crack net or a crack network. The second method, on the other hand, is used for slightly larger, more precisely: wider cracks in the exterior plaster. Such a crack is filled. Here, too, the suitable filling material can easily be found in the hardware store. Since both methods do not affect the building fabric itself, the work can easily be carried out by non-professionals.

cover crack

Covering a single crack or a network of cracks basically means nothing more than applying a new layer of plaster to the old one. This can be done partially or across the board, i.e. affecting the entire wall. To do this, you can get either so-called roll-on plaster with a grain size of 0.5 mm or a mineral plaster with a grain size of 2 mm in the hardware store. While the mineral plaster must first be mixed with water according to the manufacturer's specifications, the roller plaster can be used immediately.

Mineral plaster is applied over a large area with a so-called plaster trowel and then carefully smoothed over. The application of the roller plaster is carried out with a commercially available paint roller. It is important to reach a certain minimum strength. 15 mm is recommended. The newly plastered area then has to be painted after several days of drying.

fill crack

If you want or have to fill a crack, you need the right filling material. This is available as a dry substance and must be mixed with water according to the manufacturer's instructions. This creates a mortar-like mass, which is then poured directly into the crack with a spatula until it is completely filled. After it has dried, the affected area is generously plastered again with the mass. The plaster must be applied beyond the actual crack width.

Basic Tips

Regardless of whether you want to cover or fill cracks, it is advisable to clean the surface thoroughly beforehand. This is best done with a dampened, relatively soft brush. It is also important to only perform the work when the weather is nice and dry. It must also be ensured that it is no longer freezing outside. Since the cracks are often in places that are difficult to reach, a ladder or scaffolding is usually required. For safety reasons, preference should always be given to scaffolding. It also allows more freedom of movement. Small scaffolding can be rented for a fee at virtually any hardware store.

Learn more about plaster from A-Z - types & processing