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Causes and prevention of bad mortar cohesion

2022-12-07

Let's talk about the phenomenon of poor mortar bonding:
The fullness of the mortar in the horizontal mortar joints of masonry is lower than 80%; there are blind joints in the vertical joints, especially in the hollow brick walls, there are often more transparent joints, and the drywall is built with large shrinkage, and the depth of the shrinkage can even reach 20mm The above affects the fullness of the mortar. Bricks are not watered and wet before masonry, dry bricks are placed on the wall, or the length of plastering is too long, resulting in poor bonding of mortar and bricks.
Analysis of the causes of poor bonding between mortar and brick:
1. Low-strength mortar, such as cement mortar, due to the poor workability of cement mortar, it is laborious to squeeze the mortar during masonry. After the operator scrapes the mortar with a large shovel or a trowel, the bottom ash will produce cavities and the mortar will not be full.
2. When building walls with dry bricks, the early dehydration of the mortar will reduce the strength, the bonding force with the bricks will decrease, and the dust on the surface of the dry bricks will act as an isolation function, weakening the bonding between the bricks and the mortar layer.
3. When using the grouting method to build masonry, sometimes the masonry speed cannot keep up because the grouting is too long, and the moisture in the mortar is absorbed by the bottom bricks so that the bond between the bricklayer and the mortar is lost.
4. When laying dry walls, to save the scraping process, the method of spreading ash with a large shrinkage is adopted, so that the depth of the shrinkage of the masonry brick joints can reach more than 20mm, which not only reduces the fullness of the mortar but also increases the workload of pointing.
  Prevention:
1. Improving the workability of mortar is the key to ensuring the fullness of mortar and improving the bond strength. The choice of mortar raw material is very important. The sand cement must be within the shelf life, and the thickener cellulose ether and re-dispersible latex powder to improve the adhesion of the mortar must be selected from regular companies.
2. Improve the masonry method. It is not suitable to adopt the grouting method or laying bricks for masonry, and the "three-one bricklaying method" should be promoted, that is, the masonry method of using a large shovel, one brick, one shovel of ash, and one squeeze.
3. When the grouting method is used for masonry, the length of the grouting must be controlled. Generally, the temperature shall not exceed 750mm, and when the temperature exceeds 30°C during construction, it shall not exceed 500mm.
4. It is strictly forbidden to be used in brick walls. The bricks should be wetted 1 to 2 days before masonry so that the moisture content of sintered ordinary bricks and porous bricks reaches 10% to 15%; the moisture content of lime sand bricks and fly ash bricks reaches 8% to 12%.
5. During winter construction, the brick surface should be properly moistened under positive temperature conditions before laying bricks. When it is impossible to pour bricks during construction under negative temperatures, the consistency of the mortar should be appropriately increased. For 9-degree seismic fortification areas, masonry cannot be carried out if bricks cannot be fired in severe winter.

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