Some reasons for cracks in wall and ceiling plasters
It is sometimes observed in buildings that the plastered surfaces crack after they are dried and hardened. According to experiments and studies, such cracks can occur for one of the following reasons:
- If the weight percentage of water is higher than gypsum, because its volume decreases after the plaster dries, and it cannot fill the volume of water consumed in the mortar.
- In conditions where the mortar drawn on the wall is more than 7-8 cm thick and it is cast in one step. In this case, the top layer of plaster dries quickly because of exposure to air, while the inner layers remain wet, and in the next few hours when these layers begin to dry, cracks occur in the upper surfaces to release the vapors caused by their drying.
- If the air temperature is below zero when plastering, the water inside the mortar freezes before the plaster hardens, thereby preventing the chemical interactions required for mixture of the plaster. After the ice melts, the gypsum decomposes and does not continue to expand, in which case cracks occur on the surface.
- Some plastering cracks are caused by the subsidence of buildings, which are manifested as lines with an angle of 45 degrees.
- Sometimes the surfaces under the plaster that are exposed to heat and sunlight during the day and become cool at night expand or contract, thus causing cracks in the plaster.
- The penetration of the moisture of fresh gypsum coating to cement or limestone substrates can be another cause of cracking in the plastering process.
However, the mentioned cases are only some of the reasons for wall cracking; the plaster layer may crack due to leaking joints, construction vibrations or other reasons. The repair process involves identifying the type of cracking and fixing the problem.
