More than 10 key questions in mortar technology
1. What is
masonry mortar? What materials do masonry mortars consist of?
A: The
mortar that bonds bricks, stones, blocks, etc. into a masonry is called masonry
mortar.
The material
composition of the masonry mortar: cement, other cementitious materials (such
as lime paste, clay paste, hydroxypropyl methylcellulose, etc.), fine aggregate
and water.
2. What
should I pay attention to when choosing masonry mortar?
Answer:
Cement can choose the appropriate cement type according to the design
requirements, the masonry location and the environmental conditions. Choosing
medium and low strength cement can meet the requirements. The cement used in
cement mortar should not exceed 32.5 grades; the cement used in cement mortar
should not exceed 42.5. When the quicklime is matured into lime paste, the mesh
with a pore diameter of not more than 3 mm×3 mm should be used for filtration,
and the ripening time should not be less than 7 days; the ripening time of the
ground fine lime powder should not be less than 2 days. The lime paste stored
in the sedimentation tank should be taken to prevent drying, freezing and
pollution. It is strictly forbidden to use dehydrated and hardened lime paste.
The consistency of the lime paste used should be controlled to about 120 mm.
Sand for masonry mortar should be selected from medium sand. The coarse sand
should be used for masonry. The mud content should not exceed 5%. The cement
mortar with strength grade of M2.5 should not exceed 10 mud. %. Mix the mortar
with water, and use clean water without harmful impurities to mix the mortar.
3. What
materials are used to build the mortar? What are the construction mortars used
for?
A:
Building mortar is composed of inorganic cementitious materials (hydroxypropyl
methylcellulose, redispersible latex powder), fine aggregates and water, and
sometimes blended with certain admixtures.
Construction
mortar is often used for masonry (such as brick, stone, block) structures,
plastering of interior and exterior surfaces of buildings (such as walls,
floors, ceilings), joints of large wall panels, masonry walls, and decorative
materials. Bonding, etc.
4. What
properties should the mortar after mixing have?
Answer: The
mortar after mixing should have the following properties: meet the requirements
of workability; meet the design type and strength grade requirements; have
sufficient adhesion.
5. What are
the properties of masonry mortar? What is the content of mortar and
workability?
A: The
properties of masonry mortar include the workability of the mortar, the
strength of the mortar and the adhesion of the mortar. Mortar workability,
including fluidity and water retention, has a lot to do with the additive hydroxypropyl
methylcellulose.
6. How is
the construction mortar classified?
Answer:
Building mortar is classified according to the purpose: it can be divided into
masonry mortar and plastering mortar. The plastering mortar includes ordinary
plastering mortar, decorative plastering mortar and special mortar. Special
mortars include waterproof mortar, acid-resistant mortar, thermal insulation
mortar, sound-absorbing mortar and so on.
Construction
mortar is classified according to cementitious materials: it can be divided
into cement mortar, lime mortar and mixed mortar. Mixed mortar can be further
divided into: cement lime mortar, cement clay mortar, lime clay mortar, lime
fly ash mortar and the like.
7. What is
the fluidity of the mortar, and what are the influencing factors?
A: The
fluidity of mortar is also called consistency. It refers to the performance of
flow under the action of self-weight or external force. It is expressed by
“sinking degree”.
The degree
of sinking is large, the mortar has great fluidity, but the fluidity is too
large, and the strength will be reduced after hardening; if the fluidity is too
small, the construction operation is not convenient.
The fluidity
of the mortar is related to the types of masonry materials, construction conditions
and climatic conditions. For porous water-absorbing masonry materials and dry
and hot weather, the fluidity of the mortar is required to be larger; on the
contrary, for dense non-absorbent materials and wet and cold weather, the
fluidity is required to be smaller. The additive hydroxypropyl methylcellulose
plays the role of thickening and water retention, and the dispersible latex
powder can increase the strength and improve the overall quality of the mortar.
8. What is
the water retention capacity of the mortar, and what is the water retention
capacity of the mortar? What are the requirements?
A: The
ability of fresh mortar to retain moisture is called water retention. Water
retention also refers to the property that the various constituent materials in
the mortar are not easily separated. The appropriate hydroxypropyl
methylcellulose is selected to adjust the water retention effect of the mortar.
The water
retention of the mortar is expressed by “stratification”. The
stratification should be between 10 and 20 mm, and should not be greater than
30 mm. Mortars with a stratification of more than 30 mm are prone to
segregation and are not convenient for construction; mortars with a
stratification close to zero are prone to dry shrinkage cracks.
9. What are
the factors that affect the strength of the mortar?
A: There are
many factors affecting the strength of mortar. Experiments have shown that when
the quality of the raw materials is constant, the strength of the mortar mainly
depends on the strength grade of the cement and the amount of cement. The
strength of the mortar can also be appropriately adjusted by adding the
redispersible latex powder.
10. What are
the effects of 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 adhesion. The adhesion of
the mortar is related to the surface state, cleanliness, wetting condition and
construction and maintenance conditions of the masonry. Therefore, the bricks
before the masonry should be watered and moist, and the moisture content should
be controlled at 10%~15%. The surface should not be soiled to improve the
adhesion between the mortar and the brick to ensure the quality of the masonry.
11. How
should brick walls, slat walls or slat roofs, concrete walls, etc., and
underlying plasters that are prone to collision or moisture?
A: The
bottom layer plaster used for brick walls, mostly with lime mortar; the bottom
layer plaster used for slat wall or slat roof is mixed with mortar or lime
mortar; the concrete wall, beam, column, roof and other bottom plastering
multi-purpose mixed mortar , hemp stone mortar or paper gluten lime slurry.
12. What are
the basic requirements for masonry mortar mix design?
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 bulk density of the mixture: cement mortar <1900kg/m3; cement mixed
mortar <1800 kg/m3.
(2) The
strength and durability of the masonry mortar should meet the design
requirements.
(3) It
should be economically reasonable, and the amount of cement and admixture should
be less.
13. What are
the applications of masonry mortar in the project?
Answer:
Cement mortar should be used for masonry with high humidity and high strength;
cement lime mortar should be used for masonry in dry environment; wall of
multi-storey building is generally cement mortar with strength grade M5 Brick
mortar, brick arch, reinforced brick lintel, etc. generally use cement mortar
with strength grade M5~M10; brick foundation generally adopts cement mortar not
lower than M5; limestone mortar can be used for low-rise houses or bungalows;
lime can be used for simple houses Clay mortar.
14. What are
the requirements for plastering mortar?
A: The
mortar is required to have good workability, and it is easy to be smeared into
a uniform flat layer for easy construction. It should also have a high cohesive
force, and the mortar layer should be able to bond firmly to the bottom surface
without cracking or falling off for a long time. In a humid environment or
vulnerable to external forces (such as the ground, wall skirts, etc.), should
also have high water resistance and strength.
15. What are
the main functions of ordinary plastering mortar?
A: The
function of ordinary plastering mortar is to protect the wall and the ground
from the wind and rain and harmful impurities, improve the moisture resistance,
corrosion resistance, weathering resistance and durability, and at the same
time make the building surface smooth, clean and beautiful. effect.
16. What is
the plastering mortar? Which types can be classified according to the different
building functions of the plastering mortar?
A: Any
mortar applied to the surface of a building or building component is
collectively referred to as a mortar.
According to
the different functions of the plastering mortar, the plastering mortar can be
divided into ordinary plastering mortar, decorative mortar and plastering
mortar with certain special functions (such as waterproof mortar, thermal
insulation mortar, sound absorbing mortar, acid-resistant mortar, etc.).
17. Why is
the compressive strength often used as the main technical index of mortar in
the project? How is the strength grade of the mortar determined? What are the
strength grades of the masonry mortar?
Answer:
Mortar mainly plays the role of transmitting load in the masonry. The test
proves that the bond 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 mature, the test
is simple and accurate, so engineering The compressive strength is often used
as the main technical index of the mortar.
The strength
grade of the mortar is a cube test piece with a side length of 70.7mm. The
standard curing conditions (cement mixing mortar is 20±2°C, relative humidity
is 60%~80%; cement mortar is temperature 20±2°C, relative humidity). Above
90%), the compressive strength at 28 days of age was determined by standard
test methods.
The strength
grade of masonry mortar is M20, M15, M10, M7.5, M5, M2.5.
18. Ordinary
plastering mortar is usually divided into several layers. What is the
difference between the functions and requirements of each layer of mortar?
A: Ordinary
plastering mortar is usually divided into two or three layers for construction.
The mortar requirements vary from layer to layer, so the mortar used for each
layer is different. Generally, the bottom mortar acts as a bonding base layer,
and the mortar should have good workability and high adhesion. Therefore, the
water retention of the bottom mortar is better, otherwise the moisture is
easily absorbed by the base material and affects the adhesion of the mortar.
The rough surface of the base layer is advantageous for bonding with the
mortar. The middle plaster is mainly for leveling, sometimes it can be omitted.
The surface plastering is mainly for the sake of smoothness and beauty, so fine
sand should be selected.
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