If you look closely, cracks occur almost systematically in all buildings. Most of the time, they are harmless. But depending on their type and cause, they can be an indication of serious construction problems. Why and how do cracks form and how to identify when they are most dangerous?
Cracks due to shrinkage
So-called shrinkage cracks are among the most common types of cracks. These occur when concrete, plaster or any porous material contracts as it dries. It is a normal process, so this type of cracking can almost never be avoided. However, if the cracks are very pronounced and appear soon after construction, this may indicate that the plaster or concrete or other surface has dried too quickly. This mainly happens when the surface of the wall is heated by the sun’s rays or dried out by dry air – which is possible in both summer and winter – or even is exposed to the wind.
Cracks in a wall can also be caused by stresses from using material used in a function for which it was not designed. A classic example is the joints between the wall and the ceiling. Due to thermal changes, the components “work” causing the plaster to tear, for example. The same effect can occur with sloped ceilings that bend under wind pressure. The only way to avoid these types of cracks is to properly separate the respective surfaces. Reinforced concrete ceilings also almost inevitably crack.
A ceiling always bends slightly due to its own weight and the loads it supports. Since the tensile forces act on the underside of the ceiling and the concrete has a very low tensile strength, hairline cracks form there.
Settlement of cracks
One of the most dangerous causes of masonry cracks is differential settlement. Once a building is constructed, it settles in the ground after a more or less long time depending on the nature of the construction or the nature of the ground. The duration of the process depends on the strength of the soil – on gravel or sand it can be completed after a few months, while clay soils can “work” for decades. The house can sag a few millimeters, which is not a problem if the ground is uniformly flat. For example, if a rock is present under the construction, this can cause cracks throughout the building. Similarly, the presence of a nearby tree can cause its roots to absorb water until the soil dries out and again creates compaction. This settlement effect can also result from the effects of neighboring buildings. If the soil is reworked or backfilled, this can create depth differences and therefore compaction. It is therefore essential to examine the ground before building to determine all the irregularities and the resistance of the ground. If you skip this essential step and in addition your construction lacks rigidity, you are sure to see cracks appear, both inside and outside. Depending on their size, they can be either not very dangerous or, on the contrary, a sign of serious problems.
Detect if your crack can have dangerous consequences
The potential danger of a crack can be estimated primarily by its width and depth. Hairline cracks are no more than 0.2mm wide and are usually harmless. They generally do not compromise the integrity of the construction. When they are larger, it starts to become more of a problem. In such cases, it makes sense to observe the development of the crack. You can do this by taking regular pictures, marking the start and end of the crack with a pencil and the date, or applying a plaster mark that will tear if the crack continues to widen. If the crack develops or if other circumstances indicate a possible construction defect, it is better that you call a building expert. Fortunately, very serious problems are rare. We usually manage to repair the cracks. Even if there is no question of a structural defect, it may be a question of a crack that lets moisture pass through a metal reinforcement and causes it to rust, for example. The same applies to cracks in the facade through which rainwater can penetrate. In addition, water entering the cracks can freeze in winter and increase the damage.
How to repair cracks on the wall of your house?
Cracks in a wall can be filled in different ways. The recommended course of action mainly depends on whether the crack is outside or inside. Hairline cracks inside can often be simply painted over, with a specific paint. If the crack is wider, it can be repaired with plaster or putty.