How to reduce Cracks in AAC Block wall in Nepal

Some building experiences in Nepal say that walls made up of AAC Block develop crack problem in site. Construction of AAC Block actually started in Europe almost a hundred years ago and it started becoming prevalent in Nepal since the last decade. Brick was the building material used in wall in Nepal since ancient times. But AAC Block has gained a lot of popularity because of its ease of handling and use, being earthquake resistant, fire-resistant for a relatively longer time as compared to brick walls. Some people, however, complaint that AAC Block wall crack easily resulting in waste of material.

Here are a few suggestions or methods we are providing you for making sure you don’t develop cracks in AAC Block walls:

AAC Block Quality

As like Bricks, AAC Blocks also has 3 kinds of Quality- Standard 1, Standard 2 and Standard 3.  You must always prefer Standard 1 AAC Block in order to minimize crack appearance. The above mentioned standard numbers are based on shrinkage capacity. Standard 1 AAC Block has lowest shrinkage capacity whereas standard 2 AAC Block has high shrinkage when blocks come in contact with water.

Place the AAC Blocks above ground

It’s the best when you place AAC Blocks above ground for storage. You must maintain at least 300mm board above ground level. Placing AAC Blocks in the ground will only help it absorb water which will later shrink down to form a crack in the AAC Block wall.

Use AAC Block Joint Chemical instead of Cement Sand Mortar

People prefer to use cement sand mortar instead of AAC Block Joint thinking that AAC Block Joint Chemical is expensive. However, researches and our experience shows that AAC Block Joint chemical price is almost as same as Cement Sand Mortar. Cement Sand Mortar has water in it and water is soaked by AAC Blocks most of the time- resulting in a weak bond. If you use a chemical, joints between the AAC Blocks in the walls are stronger.

Height of AAC Block Construction

AAC Block Construction can be done for any height possible, but with structural aspects fulfilled. If you are building a parapet wall with AAC Blocks, make sure that you are constructing it only upto the height of 1200mm. When constructing internal and external walls, you must give it a sill and lintel. The sill and lintel must at least be 4 inches in thickness and have two longitudinal rebar at least of size 10mm. Sill and lintels always covers the full breadth of the wall.

Don’t Soak AAC Block in Water

When a brick wall is to be laid, IS:2212: 1991 says that the brick should be soaked for 24 hours in water before laying it out with mortar. However, AAC Blocks should never be soaked inside water. The matter of fact is AAC Blocks have high expansion and high shrinkage as compared to Brick. After drying, the AAC Block will shrink resulting in cracks.

No sill and lintel in AAC Block wall

Incase AAC Block walls are used as interior walls, the practice is to not use a sill and lintel level. This always results in a diagonal crack in case of earthquakes because there is no sill and lintel beams. Sill and lintel always covers the full breadth of wall. The portion of wall between sill and lintel, between lintel and beam and between sill and floor level act as a block during earthquakes. The lesser height of block doesn’t result in diagonal cracks.

Don’t use AAC Block Walls in Damp Areas

It has often been seen that walls made up of AAC Blocks develop cracks when used in Damp Areas. It is only because AAC Blocks soak more water and expand more than bricks. When dry, AAC Block contract faster and crack is the result. If there is any compulsion to use AAC Blocks in damp areas, you must use suitable waterproofs like bitumen and damp proof course before laying wall above it. Often in the market, brick walls are used in Damp areas because even if efflorescence happens in the brick, it doesn’t prevent result in structural weakness of wall.

Connection between AAC Block walls and Concrete

Crack below beams is a common problem often because of lack of construction ideas. To avoid horizontal crack line just below beams, The blocks should not directly be touched with the concrete beam. Cement sand mortar must be inserted and packed in between the wall and concrete beam. In case of poor workmanship, chicken mesh must be placed longitudinally between wall and beam and then plaster works should be carried out in order to avoid horizontal cracks.