Why does AAC block crack?
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Why does AAC block crack?

Views: 262     Author: Site Editor     Publish Time: 2022-05-26      Origin: Site Inquire

AAC block is a new type of eco-friendly wall material. It is made of fly ash, lime, cement, gypsum, aluminium paste, water, release agent and other raw materials, and is produced through the steps of slurry making, casting and cutting, and high-pressure steam maintenance.


AAC blocks are mainly used in non-load bearing wall masonry and frame structure filling, which is now a popular building material in the global construction industry. AAC blocks will encounter different problems during their production, and this blog will give you an introduction to the causes of cracks in AAC blocks and some tips for maintenance and storage.

Why does AAC block crack?

1. Uneven slurry

Because the density and self-weight of the material are different, plus the possibility of uneven mixing, it is easy to result in the phenomenon of stratification of the slurry when it comes to a static stop, and then it will cause cracks in the blank.

2. Uneven temperature

After the slurry is injected into the mould, it enters the static stopping room for pre-feeding. The temperature of the static stopping room is not stable, resulting in inconsistent temperature at various points in the billet, which generates temperature gradients and cracks on the surface of the billet.

3. Static stop time is too long

Statistics have found that if the static stopping time is more than 3 hours, the top and sides are likely to have large cracks, but when the static stopping time is too short, less than 3 hours, the hardness of the billet may not meet the requirements, and can not be sent to the cutting machine to cut, or the steam raising causes collapse accidents.

4. Reasons for raw materials

If the fly ash used in the production of AAC bricks has a large sieve margin and the particles are coarse, its slurry suspension performance will become poor, and the surface will be seriously waterlogged after entering the mould, coupled with the small viscosity, the slurry limit shear stress grows slowly. Unstable bubbles caused by slow thickening are also the cause of cracks in the billet.

5. Dry shrinkage cracks

Sometimes, the AAC block cannot be sent into the steam kettle immediately for steaming after cutting. As the temperature decreases, the billet is deformed due to the cold shrinkage of the aggregate, and small cracks will appear on the outer surface.

How to avoid cracks?

Cracks are very likely to appear in certain corners of AAC walls. Therefore, it is always recommended to add nominal reinforced concrete bond beams at lentils and thresholds. The bond beam prevents shear stresses on the wall and therefore prevents cracks from forming on the wall due to shear stresses.

Tips for storing AAC blocks

When storing AAC blocks, you should consider these factors below to achieve effective results:

  • Avoid contact with water when storing masonry blocks.

  • Avoid using wet blocks during the masonry process. If by chance you find that the blocks have become wet, they must be dried before use.

  • Alternately stack blocks to avoid chipping at corners.

  • If these AAC blocks are installed in an environment with high humidity, then make sure the moisture vapour penetration is low on interior walls and high on exterior walls.

Advice on pre-work preparation

Please make sure to check the points of these pre-work preparations to be done for better results.

  • For interior walls use AAC internal wall blocks of at least 100 mm thickness. And for exterior walls, use AAC external wall blocks of at least 150 mm.

  • If the thickness of the blocks is less than the recommendation, then make appropriate design changes.

  • Holes in the blocks to support scaffolding must be avoided. You should incorporate scaffold supports in the concrete.

Final Thoughts

If you are looking for a reliable manufacturer that offers quality AAC products including AAC blocks and AAC panels, you should definitely check out Ecotrend. They offer quality AAC building materials which will bring efficient and fruitful results.