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Why does mortar crack when drying?

March 23, 2023 jinchen 0 Comments

Mortar is an essential material in construction, used to fill gaps in walls, floors, and masonry to enhance the stability and durability of the structure. However, cracking often occurs during the drying process of mortar, which can seriously affect the quality and aesthetics of the building. So why does mortar crack when it dries? This article will explore this issue in-depth and provide some suggestions for avoiding mortar cracking.

Why does mortar crack when it dries?

Material quality issues

First, the quality of the materials in the mortar is an important factor in cracking. If the sand, cement, and other materials used are of poor quality or not properly proportioned, the mortar can become too dry or have excessive water content, leading to cracking. Therefore, when choosing materials, make sure to select reliable quality materials and adjust the proportions according to the intended use and environmental factors of the mortar.

Temperature issues

The drying speed of mortar is closely related to temperature. During the drying process, if the temperature is too high or too low, it can cause mortar cracking. At high temperatures, the surface moisture of the mortar evaporates quickly, but the internal moisture still exists. When the surface mortar dries, the internal moisture evaporates due to the high temperature, generating vapor pressure, causing the mortar to crack.

At low temperatures, the drying speed of the mortar slows down, and the evaporation rate of the moisture is slower, causing the internal moisture content of the mortar to be too high, leading to cracking. Therefore, during construction, it is essential to choose an appropriate temperature period for construction and increase ventilation and heating equipment to speed up the mortar drying process.

Humidity issues

In addition to temperature, humidity is also an important factor in mortar cracking. High humidity can cause the surface moisture of the mortar to not evaporate sufficiently, leading to excessive internal moisture and cracking. Low humidity can cause the internal moisture of the mortar to evaporate quickly, while the surface moisture content is low, leading to an imbalance of moisture between the surface and the interior, which can also cause the mortar to crack. Therefore, during the construction process, pay attention to controlling indoor humidity and ventilation conditions to avoid environments with excessively high or low humidity.

Construction technique issues

Mortar cracking is also related to construction techniques. During construction, it is essential to pay attention to the thickness, compactness, and application methods of the mortar to avoid excessive application or compaction, causing excessive stress in the mortar and leading to cracking. Also, minimize vibration and compression of the mortar during construction to avoid stress and structural damage.

Environmental factors

Environmental factors can also cause mortar cracking. For example, the quality and stability of building materials are affected by climatic conditions and the surrounding environment. In construction, if environmental factors such as temperature, humidity, and wind change, it may cause mortar cracking. Additionally, if the foundation settlement or imbalance of a building leads to structural deformation, it can also cause mortar cracking.

How to prevent mortar cracking?

Control construction environment

To prevent mortar cracking, the construction environment needs to be strictly controlled. During construction, avoid working in high temperatures, low humidity, strong winds, and strong sunlight to reduce the possibility of uneven evaporation of moisture inside the mortar. Choose appropriate temperature, humidity, and good ventilation for construction, and ensure suitable ventilation and humidity conditions in the construction area.

Properly adjust the mortar mix ratio

A proper mortar mix ratio is the key to preventing mortar cracking. Choose high-quality sand, cement, and other materials and mix them in the appropriate proportions to ensure the quality and stability of the mortar. When adjusting the mix, make appropriate adjustments according to factors such as environmental temperature and humidity to ensure the quality and stability of the mortar.

Make good use of anti-cracking agents

Anti-cracking agents are chemical additives that can increase the extensibility of mortar and reduce the risk of cracking. Adding an appropriate amount of anti-cracking agent to the mortar can increase the extensibility and flexibility of the mortar, thus reducing internal stress and preventing cracking. However, the use of anti-cracking agents should be scientifically and reasonably proportioned according to the use environment and material characteristics; otherwise, it may increase the risk of mortar cracking.

Precise construction

Precise construction is an important measure to prevent mortar cracking. During construction, pay attention to the thickness, compactness, and coating method of the mortar to avoid excessive coating or compaction, which can produce excessive stress. During construction, try to minimize the vibration and squeezing of the mortar to avoid creating stress and damaging the structure.

Strengthen quality supervision

Strengthening the quality supervision of mortar is another key to preventing cracking. During construction, strictly follow the specifications and ensure that the mortar mix ratio, construction technology, and other aspects meet the specifications. At the same time, conduct full-process quality monitoring and acceptance to ensure that the quality of the mortar meets the specified standards.

How to deal with cracked mortar?

If cracked mortar is found, it needs to be dealt with promptly to prevent the cracking area from expanding. The specific treatment methods include the following:

Clear the cracks

First, clear the cracks and the loose parts around them to ensure the compactness and adhesion of the mortar. Steel wire brushes, scrapers, and other tools should be used to clean the cracks and the surrounding mortar surface.

Fill the cracks

After clearing the cracks, use the corresponding mortar materials to fill them. Select mortar materials that meet the specifications, mix them according to the prescribed ratio, and ensure the quality and stability of the mortar. When filling the cracks, pay attention to the compactness and uniformity of the mortar application to ensure the effectiveness of the repair.

Prevent re-cracking

After filling the cracks, measures need to be taken to prevent re-cracking. The humidity and ventilation in the room can be controlled, and anti-cracking agents can be added to improve the extensibility and flexibility of the mortar, reduce internal stress, and prevent re-cracking.


Mortar cracking is a common problem in construction, but it can be prevented and solved. During construction, attention should be paid to the mortar mix ratio, construction environment, and quality supervision to minimize internal stress and damage to the mortar and avoid cracking. If the cracked mortar is found, prompt treatment should be carried out using appropriate repair methods to prevent the cracks from expanding or causing other problems. Only through scientific and reasonable construction and effective treatment measures can the quality and stability of mortar be ensured and the safety and sustainability of buildings be guaranteed.

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