The new type of building materials aerated block is the most used environmental protection and energy-saving wall material in recent years. It is formed by using silicon and calcium materials through milling, mixing, foaming and steaming. It has the characteristics of light weight, heat preservation, fire prevention and moisture resistance. However, the surface of the aerated block is smooth, loose and porous, and has poor adhesion. It is prone to water seepage, resulting in hollow cracks on the wall. The main reasons leading to hollow cracks in aerated block walls:
1. Aerated blocks have large shrinkage, high water absorption but poor moisture conductivity. The shrinkage value of the aerated block after leaving the kettle changed greatly within 28 days, and then gradually stabilized. Dry aerated blocks will absorb the moisture of the plaster layer and affect the strength and cohesiveness of the mortar. In addition, the surface of the aerated block evaporates quickly. Due to the poor moisture conductivity, the internal evaporation is slow, which causes the evaporation of the block and the plaster layer to be asynchronous, resulting in a difference in the drying value, and the mortar is separated from the block.
2. The surface of the aerated block after cutting is fish-scaled with loose particles, which leads to a decrease in the viscosity between the block and the plaster layer.
3. The different sizes of aerated blocks result in different widths of mortar joints, different thickness of plastering, and differences in shrinkage and deformation. In addition, the damage of the block can also lead to the hollowing phenomenon of the wall.
4. The block size is too large, the mortar joint is small, and the wall wall has insufficient fixing force to the plaster layer, which is easy to cause the plaster surface to hollow.
5. The quality of the mortar is poor. The mortar has poor water retention and is easily absorbed by the blocks to harden the mortar. Or it may be caused by poor quality of mortar raw materials and insufficient cement stability. When the strength of the mortar is too large, the elastic modulus is also high, and the pressure generated by the shrinkage value is also high. This pressure exceeds the tensile capacity of the mortar and causes cracking. 6. Construction operation problems. The mortar joints of the blocks did not meet the requirements, the uneven walls caused the ash layer to be too thick, the aerated blocks and the beams, slabs, and columns were not densely embedded according to the design requirements, and the plastering was not carried out in layers. The doors and windows were not connected to the blocks. Wait fast.
Solutions to the phenomenon of hollow cracks on the wall:
1. The age of the aerated blocks used should be more than 28 days before leaving the factory, and the blocks should be protected from rain. Water can be properly watered two days in advance when laying masonry. Strictly control the thickness, verticality and saturation of the ash joint. When the wall is built close to the beam and the bottom of the slab, a certain gap should be left, and after a rest for at least 7 days, it should be repaired and squeezed; C20 fine stone concrete can also be used to plug it tightly and fill it tightly. When building blocks on the floor, 4 ordinary clay bricks should be laid first to avoid hollowing and cracks when making the cement skirting.
2. Whether using aerated concrete for masonry mortar or plastering mortar, the adaptability of the mortar to the substrate is very important, and how to improve the crack resistance of the plastering mortar is especially important. With the increase in the amount of aerated concrete, the requirements for the plastering mortar system used in this special requirement will inevitably appear.
3. Wall cleaning, cleaning, focusing on removing floating dust and fish scale particles, and other stains, oil stains, dust and other dirt should also be cleaned up. In addition to cleaning and cleaning, the key is to control the moisture content of the wall. A more successful method is to sprinkle water on the wall 3 times, and control the watering time for about 20 minutes each time. After sprinkling the water for the third time, when the surface of the wall appears to be dry but not dry, shake it immediately. The standard for testing the quality of sprinkling water is based on the 8-10mm of the water penetrating the surface of the aerated concrete block.
4. Because the temperature and humidity deformation of reinforced concrete and aerated concrete masonry are inconsistent, cracks are prone to appear at the joints. The effective prevention method is to apply a layer of special bonding mortar to the joints first, and then paste a glass fiber mesh cloth with a width of 100-200mm, spread it on the surface of the bonded mortar, and wipe it with a trowel while patting it. The final mortar plastering is carried out based on the slurry output. The formal use of aerated blocks also requires continuous promotion and learning, and the block installation process should be strictly installed when using it.
