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Frequently asked questions and answers about mortar

Time£º2024/5/3Author£ºadminClick£º 890

1.What materials are used to make building mortar? What are the commonly used aspects of building mortar?

Answer: Building mortar is composed of inorganic cementitious materials, fine aggregates, and water, with certain admixtures added as needed.

Building mortar is commonly used for masonry structures (such as bricks, stones, and blocks), plastering of internal and external surfaces of buildings (such as walls, floors, and ceilings), pointing of large wall panels and brick and stone walls, and bonding of decorative materials.


2.How is construction mortar classified?

Answer: Building mortar can be classified into masonry mortar and plastering mortar according to their uses. The plastering mortar includes ordinary plastering mortar, decorative plastering mortar, and special mortar. Special mortar includes waterproof mortar, acid resistant mortar, insulation mortar, sound-absorbing mortar, etc.

Building mortar can be classified into cement mortar, lime mortar, and mixed mortar according to the cementitious materials. Mixed mortar can be further divided into: cement lime mortar, cement clay mortar, lime clay mortar, lime fly ash mortar, etc.


3. What is masonry mortar? What materials are used to make masonry mortar?

Answer: The mortar used to bond bricks, stones, blocks, etc. into masonry is called masonry mortar.

The material composition of masonry mortar includes cement, other cementitious materials (such as lime paste, clay paste, etc.), fine aggregates, and water.


4.What should be noted when selecting masonry mortar?

Answer: Cement can be selected according to design requirements, masonry location, and environmental conditions. Choosing cement with medium to low strength can meet the requirements. The cement used in cement mortar should not have a strength grade greater than 32.5; The strength grade of cement used in cement mixed mortar should not exceed 42.5.

When quicklime is matured into lime paste, a sieve with a pore size of no more than 3mm x 3mm should be used for filtration, and the maturation time should not be less than 7 days; The maturation time of finely ground quicklime powder shall not be less than 2 days. Measures should be taken to prevent drying, freezing, and contamination of the lime paste stored in the sedimentation tank. It is strictly prohibited to use dehydrated and hardened lime paste. The consistency of the lime paste used should be controlled at around 120mm.

The sand used for masonry mortar should be medium sand, and coarse sand should be used for rubble masonry, with a mud content not exceeding 5%; The cement mixed mortar with a strength grade of M2.5 should have a mud content of no more than 10%.

The water used for mixing mortar should be clean water without harmful impurities.


5.What properties should the mortar after mixing have?

Answer: The mixed mortar should have the following properties: meet the workability requirements; Meet the requirements of design types and strength levels; Has sufficient adhesive strength.


6.What are the properties of masonry mortar? What are the contents of mortar and workability?

Answer: The properties of masonry mortar include its workability, strength, and bonding strength.

Mortar workability includes fluidity and water retention.


7.What is used to represent the fluidity of mortar and what are the influencing factors?

Answer: The flowability of mortar, also known as consistency, refers to the performance of flowing under its own weight or external force, expressed as "sinking degree".

The sinking degree is high, and the mortar has high fluidity, but if the fluidity is too high, the strength will decrease after hardening; If the liquidity is too small, it is not convenient for construction operations.

The fluidity of mortar is related to factors such as the type of masonry material, construction conditions, and climatic conditions. For porous and water absorbing masonry materials and dry and hot weather, it is required that the mortar has greater fluidity; On the contrary, for dense and non absorbent materials and humid and cold weather, less fluidity is required.


8. What is the water retention of mortar, what is the representation of the water retention of mortar, and what are its requirements?

Answer: The ability of fresh mortar to retain moisture is called water retention, which also refers to the properties of the various components in the mortar that are not easily separated.

The water retention of mortar is represented by the degree of layering.

The layering degree should be between 10-20mm and should not exceed 30mm. Mortar with a layering degree greater than 30mm is prone to segregation and inconvenient for construction; Mortar with a layering degree close to zero is prone to dry shrinkage cracks.


9.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 a role in transmitting loads in masonry. Experimental results have shown that the bonding strength and durability of mortar increase with the increase of compressive strength, indicating a certain correlation between them. Moreover, the testing method for compressive strength is relatively mature, and the testing is simple and accurate. Therefore, compressive strength is often used as the main technical indicator of mortar in engineering.

The strength grade of mortar is determined by measuring the compressive strength of a cube with a side length of 70.7mm under standard curing conditions (cement mixed mortar at a temperature of 20 ¡À 2 ¡æ and a relative humidity of 60%~80%; cement mortar at a temperature of 20 ¡À 2 ¡æ and a relative humidity of over 90%) using standard testing methods at a 28 day age.

The strength grades of masonry mortar include M20, M15, M10, M7.5, M5, and M2.5.


10.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 constant, the strength of mortar mainly depends on the cement strength grade and cement dosage.


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

Answer: The bonding strength of masonry mortar increases with its strength, and the higher the strength grade of the mortar, the greater the bonding strength. The bonding strength of mortar is related to the surface condition, cleanliness, moisture content, and construction and maintenance conditions of bricks and stones. Therefore, before masonry, the bricks should be moistened with water, with a moisture content controlled at around 10%~15%. The surface should not be contaminated with soil to improve the bonding strength between mortar and bricks and ensure the quality of masonry.



12.What basic requirements should be met in the design of masonry mortar mix proportion?

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

(1) The workability of the mortar mixture should meet the construction requirements, and the volumetric density of the mixture: cement mortar ¡Ü 1900kg/m3; Cement mixed mortar ¡Ü 1800 kg/m3.

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

(3) Economically reasonable, the amount of cement and admixtures should be relatively small.


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

Answer: Cement mortar is suitable for masonry in damp environments and masonry with high strength requirements; Cement lime mortar is suitable for masonry in dry environments; The walls of multi story houses are generally made of cement lime mortar with a strength grade of M5; Brick columns, brick arches, reinforced brick lintels, etc. generally use cement mortar with strength grades of M5~M10; Brick foundations generally use cement mortar not less than M5; Low rise houses or bungalows can use lime mortar; Simple houses can use lime clay mortar.


14. What are the requirements for plastering mortar?

Answer: The plastering mortar should have good workability and be easy to apply into a uniform and flat thin layer for easy construction. There should also be high bonding strength, and the mortar layer should be able to bond firmly with the bottom surface, without cracking or falling off for a long time. In damp environments or areas susceptible to external forces (such as floors, wall skirts, etc.), it should also have high water resistance and strength.


15.What are the main functions of ordinary plastering mortar?

Answer: The main function of ordinary plastering mortar is to protect walls and floors from wind, rain, and harmful impurities, improve moisture resistance, corrosion resistance, and weathering resistance, and increase durability; At the same time, it can achieve a smooth, clean, and aesthetically pleasing effect on the surface of the building.


16. What is plastering mortar? What are the different types of plastering mortar that can be classified based on their different functions?

Answer: Any mortar applied to the surface of buildings or building components is collectively referred to as plastering mortar.

According to the different functions of plastering mortar, it can be divided into ordinary plastering mortar, decorative mortar, and plastering mortar with certain special functions (such as waterproof mortar, insulation mortar, sound-absorbing mortar, acid resistant mortar, etc.).


17. How many layers of ordinary plastering mortar are usually used for construction? What are the different roles and requirements of each layer of mortar?

Answer: Ordinary plastering mortar is usually divided into two or three layers for construction. The requirements for each layer of mortar are different, so the mortar selected for each layer is also different. Generally, the bottom layer mortar plays a role in bonding the base layer, requiring the mortar to have good workability and high bonding strength. Therefore, the water retention of the bottom layer mortar is good, otherwise water is easily absorbed by the base layer material and affects the bonding strength of the mortar. Roughness on the surface of the base layer is beneficial for bonding with mortar. The middle layer of plastering is mainly for leveling, and sometimes it can be omitted. The surface layer plastering is mainly for leveling and aesthetics, so fine sand should be selected.


18. How to select the bottom plastering of brick wall, Flat noodles wall or Flat noodles ceiling, concrete wall, etc., and places easy to collide or damp?

Answer: For the bottom plastering of brick walls, lime mortar is often used; For the bottom plastering of Flat noodles walls or Flat noodles ceilings, mixed mortar or lime mortar is commonly used; The bottom layer plastering of concrete walls, beams, columns, top plates, etc. is often done with mixed mortar, hemp knife lime slurry, or paper reinforced lime slurry.

In areas prone to collision or moisture, cement mortar should be used. Generally, 1:2.5 cement mortar is used in areas such as wall skirts, baseboards, floors, canopies, window sills, as well as water pools and wells.

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