There is a difference in how serious cracks in the plinth are. Cracks that develop should be repaired as soon as possible so that you avoid them getting bigger and thereby creating more problems for your house.
The plinth is one of the most exposed places on the house, as it is in close contact with damp and cold soil. It is not unusual for there to be cracks in the plinth.
Some types of plinth cracks should be repaired relatively quickly, as they can develop and thereby cause greater damage to your house. As a homeowner, you should therefore always be aware of whether cracks appear in the plinth of the house.
Damage due to cracks in the plinth
Cracks in the plinth can, for example, cause water to penetrate behind the plinth plaster, whereby the moisture level in the plastered surface of the plinth rises. When the cold comes, the accumulated moisture will expand, causing the plaster to loosen its grip on the substrate.
Moisture can also penetrate behind the plastered surface and make the plinth itself damp. This can cause moisture problems inside the house.
When the plaster peels off, the plinth will be left without the plinth plaster’s protective layer. If the plinth is left unprotected, the degradation of the plinth will accelerate. If you don’t do anything about the damage, it will develop over a very short number of years.
What is the difference between subsidence cracks and superficial cracks?
Basically, cracks in plinths can be divided into 2 types: Subsidence cracks and superficial cracks.
- A subsidence crack is known by the fact that the crack continues from the plinth up into the masonry. In general, a distinction is also made between subsidence cracks that develop and subsidence cracks that do not develop.
- A superficial crack is limited to the plinth alone.
If the cracks develop, it indicates that it is a sentence in progress. The faster they develop, the worse the problem. Sentences in progress must therefore be stopped as soon as possible so that the damage is limited as much as possible.
If the cracks do not develop, you can take it easy and have them repaired on occasion.
The importance of the substrate for cracking
A plinth typically consists of a surface of plaster on a base of brick/clinker, concrete or lightweight clinker blocks/LECA blocks.
The shape and appearance of the cracks depends to some extent on the substrate:
- On a brick substrate, fine cracks can be seen with a curved course, where a hollow sound is clearly heard when a light knock on the surface is made.
- On a concrete substrate, cracks can be seen with a more straight course, where a hollow sound can also be heard with a light knock. In addition, minor cracks can be seen which have arisen as a result of shrinkage in connection with the hardening of the plaster.
- On a base of light clinker, periodic vertical cracks can be seen that appear in the joints between the light clinker blocks. These cracks occur due to shrinkage in connection with the hardening of the plaster.
The cracks are cut to a width and depth of approx. 2 cm. This is done most easily with a small angle grinder with a stone blade. Remember to remove any adjacent loose plaster.
The exposed areas are cleaned of dust and loose plaster and “washed” – i.e. apply a thin mortar mixture, immediately before plastering again.
It is plastered again with bastard mortar. When the surface is dry to the touch, the surface is sanded with a sanding board, and the edges are straightened with a brush or a damp sponge.
Of course, there can be great variation in how cracks look, so the above is only indicative.
Superficial cracks, where a hollow sound is heard when you tap lightly on the wall, are a sure sign of hollow plaster, which will peel off sooner or later. This hollow plaster is also called shriveled plaster.
The cracks that occur in connection with shriveled plaster lead to flaking, which must be repaired before they develop.
Note that areas with hollow plaster can also occur on brickwork without cracks.
Small cracks without loose plaster are called pig cracks. Shrinkage cracks do not have a major impact on the construction of the house, and you do not need to do anything about them, unless the cracks may be develops into areas of loose plaster. However, it is important to establish that these are not sentence cracks! If you are in doubt, consult a building expert, e.g. an engineer or a building designer.
Subsidence/settlement damage
Settlement damage can be caused by the house not being stable enough, or the house’s foundation not being in order, or the ground under the foundation not being stable. This type of error can originate from the time the house was built, because, for example, it was not taken into account that the ground was soft, or because the foundation was not sufficiently built, i.e. that the foundation was not supported properly in connection with the construction itself.
Settlement damage can also occur if the soil under the house is washed away in connection with cloudbursts or due to a break in a sewer or water pipe, which causes the soil around the plinth to be washed away.
Subsidence cracks that develop can be caused by:
- That the ground under the house sinks as a result of the house’s weight exceeding the ground’s bearing capacity.
- That there has been a lowering of the groundwater level. Groundwater lowering can cause the previously water-filled soil layers to sink.
- Vibrations in the neighborhood as a result of major construction works, pile foundations or heavy traffic.
- Clefts that do not develop can be caused by:
- That a balance has been achieved between the weight of the house and the ground under the house. This balance can occur after a certain number of years and is typically seen in older properties.
- That the foundation has been strengthened, and the house as a result now stands firm.
- A leaking sewer that undermines the ground beneath the foundation.
- drying out of the ground under the house, e.g. after a long dry summer.
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