Sometimes the wall plaster cracks in buildings, especially old buildings. Even ceiling and wall cracks can be seen in newly renovated and newly constructed buildings. The state and manner of the cracks are different, sometimes these cracks are shallow and can be easily repaired, but in some cases, they may be caused by the settlement of the building. Do you have cracks in the ceiling and wall of your house and you don’t know the reason? In this article, we examine all the things that cause cracks in building plaster.

What is the cause of cracked building plaster?

In some buildings, plastering cracks after drying and hardening. These cracks have many causes, in this section we have investigated the reason for plaster cracking.

The presence of residual water vapor in plaster layers

The reason for cracks in the plaster of the building ceiling plaster, especially in newly built buildings, is due to the thickness of the mortar that is spread on the wall. If the thickness of the mortar applied on the ceiling and wall is 7 to 8 cm, the upper layers of the plaster will dry faster due to the proximity of the air, while the lower layers are still wet, and the remaining moisture in the lower layers will cause the plaster to crack.

The weight percentage of water is not proportional to plaster

One of the main reasons for cracks in ceiling and wall plaster is due to the mismatch between plaster and water. If the amount of gypsum compared to water in the plastering mortar is less so that it cannot fill the volume of water used in the mortar after expansion, the plaster will decrease in volume after drying and crack.

The movement of the mortar in the layers is the reason for the cracking of the wall plaster

The relative movement of the adjacent components of the building’s rigidity causes the plaster wall to crack. Also, the rapid setting of mortar and the loss of mortar in the lower layers are the cause of cracks in the plaster wall of the building, which are usually tiny and can be solved with paint and repair.

Plastering in cold weather causes cracking of ceiling and wall plaster

One cause of plaster cracking after drying, especially in the wall of newly built houses, is plastering in winter and cold weather. If plastering is done in cold weather and below zero degrees, the water in the plaster mortar freezes before it dries and hardens, and the chemical process to harden the mortar stops, and after the ice melts, the plaster is spoiled and no longer expands. and as a result, the plaster surface cracks.

The settlement of the building is the reason for the cracking of the plaster in the old walls

Building settlement is another cause of plaster wall cracking, if these cracks are related to asymmetric cracks, they appear at an angle of 45 degrees to the horizon, and if they are related to symmetrical settlements, they are created horizontally.

Cracks in the wall behind the heater and other pipes

Cracks occur due to expansion and contraction of walls on metal columns or windbreaks or where chimney pipes are placed. In plastering training courses, it is recommended to cover the metal parts and pipes of the heaters with chicken wire before plastering to prevent cracks in the plaster of the building. Also, sticking the heater pipe to the wall causes its heat to create cracks in the wall behind the heater. To prevent cracking of the wall plaster in this area, install the heater pipe at a distance from the wall or cover the pipe with thermal insulation.

Water leakage in the building and humidity cause vertical and horizontal cracks in the wall

One of the common causes of plaster wall cracks is water leakage inside the wall and worn out pipes and poor implementation of building plumbing. Any moisture in the wall will damage it in long time.

The weakness of some parts of the plaster wall

In newly built buildings, the weakness of parts of the plaster wall causes the wall to crack. Some parts of the plaster wall of the building, such as the sides of the wall, door and window frames, and the space between the floor and the staircase, are inherently weak and prone to cracking.

Heavy vibrations in the wall

Disasters such as earthquakes, large civil constructions near the building, and installation of heavy equipment, etc., cause vibration and ultimately cause the wall to crack.

Cement shrinkage is the reason for plaster wall cracking

Building materials such as concrete change shape and shrink over time, cause the plaster coating on the wall to crack.

Types of cracks in building plaster

There are different types of cracks in ceiling and wall plaster and they are divided into different categories:

Construction cracks in terms of structure

In terms of structure, cracks are divided into two types: structural and non-structural.

Cracks that occur due to poor design and execution and endanger the safety of the building are called structural cracks. These types of cracks occur in beams, columns, building foundations and slabs, and their depth is 1 to 1.5 cm. These cracks are very dangerous and must be repaired as soon as possible to prevent the possible collapse of the building.

Non-structural cracks: Cracks that are caused by temperature, increased loads on building components, frost, etc., are called non-structural cracks.

Old and new cracks

Another type of crack classification in the building is the division into two types, old and new.

If the thickness of the crack on the wall increases over time, it is said that the crack is new. When faced with this type of crack, we first stop its progress and then take the necessary measures to repair it. Also, cracks that do not grow are also called old cracks.

Building cracks in terms of direction 

Building cracks are divided into three vertical, horizontal and diagonal modes.

Vertical cracks are very important if they are deep.

Cracks with an angle of 45 degrees to the horizon are called diagonal cracks, which are very dangerous.

Construction cracks in terms of crack width

Construction cracks have different widths. Cracks with a width of less than 1 mm are called thin cracks, cracks with a width of 1 to 2 mm are called medium cracks, and cracks greater than 2 mm are called thick cracks.

Methods to prevent plaster cracking

Using chicken wire, rabbits and other materials to prepare the plastering area.

In the place where chimneys and hot water pipes pass, thermal insulation and wire mesh should be used to prevent the effect of heat on plastering.

The use of special fibers in the preparation of plaster mortar

Strict adherence to proportions of raw materials for plastering

Plastering when the temperature is suitable and also avoid large fluctuations in temperature when the mortar is drying.

Crack repair methods:

Before attempting to repair the crack, we must first identify its type and reason, and after identifying it, use a trowel, putty, color appropriate to the plaster wall, and sandpaper to fix it. In this part of the article, we are going to teach one of the simple methods to repair surface cracks.

To remove the crack from the wall, first you need to deepen the existing crack with a spatula, then clean the dust around the crack with a clean cloth, then cover the crack with a sticky fiberglass net. After the putty dries, rub it with relatively hard sandpaper until it is smooth and uniform. And after it is completely dry, paint it until it is the same color as the wall.

Bolour Gatch Saveh

In this article we examined 10 causes of cracks in new and old plaster and learned about the types of cracks. We also taught how to prevent cracks and repair wall cracks. Be sure to remember that before repairing the crack, check the type and depth of the crack, and if the crack is deep, seek help from an expert in construction.