FAQ about the use of mortar

1. What is the water retention of mortar? How is the water retention of mortar expressed? What are the requirements?

Answer: The ability of freshly mixed mortar to retain water is called water retention. Water retention also refers to the property that the various components in the mortar are not easy to separate.
The water retention of mortar is expressed by “stratification degree”. The stratification degree should be between 10 and 20 mm and should not be greater than 30 mm. Mortar with a stratification degree greater than 30 mm is prone to segregation and is not convenient for construction. Mortar with a stratification degree close to zero is prone to shrinkage cracks.

2. Why is compressive strength often used as the main technical indicator of mortar in engineering? How is the strength grade of mortar determined? What are the strength grades of masonry mortar?

Answer: Mortar mainly plays the role of transferring load in masonry.
Experiments have shown that the bonding strength and durability of mortar increase with the increase of compressive strength. That is, there is a certain correlation between them, and the test method of compressive strength is relatively mature. The test is relatively simple and accurate, so compressive strength is often used as the main technical indicator of mortar in engineering.

The strength grade of mortar is based on a cubic test block with a side length of 70.7mm. Under standard curing conditions (cement mixed mortar is at a temperature of 20±2℃ and a relative humidity of 60%~80%. Cement mortar is at a temperature of 20±2℃ and a relative humidity of more than 90%), the compressive strength at 28 days is determined by the standard test method. The strength grades of masonry mortar are M20, M15, M10, M7.5, M5, and M2.5.

3. What are the factors that affect the strength of mortar?

Answer: There are many factors that affect the strength of mortar. Experiments have shown that when the quality of raw materials is certain. The strength of mortar mainly depends on the cement strength grade and cement dosage.

4. What factors affect the bonding strength of masonry mortar?

Answer: The bonding strength of masonry mortar increases with the increase of its strength. The higher the mortar strength grade, the greater the bonding strength. The bonding strength of mortar is related to the surface state, cleanliness, wetness and construction and maintenance conditions of bricks and stones.

Therefore, bricks should be watered and moistened before masonry. The moisture content should be controlled at about 10%~15%, and the surface should not be stained with mud to improve the bonding strength between mortar and bricks and ensure the quality of masonry.

5. What basic requirements should be met in the design of masonry mortar mix ratio?

Answer: The design of masonry mortar mix ratio should meet the following basic requirements:

(1) The workability of the mortar mixture should meet the construction requirements, and the volume density of the mixture: cement mortar ≮1900kgm3; cement mixed mortar ≮1800 kgm3.

(2) The strength and durability of masonry mortar should meet the design requirements.

(3) It should be economically reasonable, and the amount of cement and admixtures should be small.

6. What are the applications of masonry mortar in engineering?

Answer: Cement mortar is suitable for masonry in humid environments and masonry with high strength requirements. Cement lime mortar is suitable for masonry in dry environments.

The walls of multi-story houses generally use cement lime mortar with a strength grade of M5. Brick columns, brick arches, reinforced brick lintels, etc. generally use cement mortar with a strength grade of M5~M10.

Brick foundations generally use cement mortar of not less than M5. Lime mortar can be used for low-rise houses or bungalows. Lime clay mortar can be used for simple houses.