Cracks in AAC Blocks Wall – Causes and Repair

Queryasked by Ankush Kaul

I recently got my new construction done. I used 10 cm AAC blocks. I even got it plastered and cured well for 3 weeks twice a day. Post which I got it putty done. After two to three months now the hairline cracks started appearing over the walls in random directions (vertical, horizontal and diagonal.) Looks like map pattern according to what you explained in other links.It is on 2nd floor construction. The structure is RCC structure. The number of cracks are increasing at different locations. I wanted to know could it be because of AAC blocks or fine sand used. How do I repair it and should I wait for few months to see if more cracks are happening. What mortar or chemical or grout should I use. The size of cracks is not more than 1 mm.

Solutionby Gharpedia

Use of AAC blocks to construct a wall is not the reason of cracks unless blocks quantity is very bad. There are many reasons which cause cracks like crazing and spider web pattern, such cracks are observed at many places. Here are the reasons which may be the cause of cracks on your wall:

• Shrinkage in blocks or poor quality of blocks may also cause a crack in a wall.
• Use of higher grade of cement to make mortar.
• Use of rich cement mortar i.e. the cement content is higher than specified in the design mix.
• Use of very fine sand to make mortar i.e. higher silt content or use of sand which is not graded properly.
• Higher water cement ratio in mortar mix.
• Improper curing.
• Poor workmanship.
• Higher thickness of plaster.
• Early application of putty i.e. putty is applied just after curing.
• A temperature at the time of application of plaster. i.e. shrinkage cracks are more prone in summer season than the winter.
• Humidity at your location. i.e. relative humidity in the coastal region is high through the year hence this area is less prone to the cracks.
• Continuous vibration or frequent hit by a hammer for nailing may also be a reason of cracks in a wall.

Also Read: Classification of Cracks: Nature-wise, Width-wise & Shape-wise

As such these types of cracks are not harmful. They are just shrinkage crack which is non-structural cracks and hence not dangerous, but it gives a bad and unpleasant look. Hence, first of all, there is no need to get frightened. This will not cause a collapse of a house or wall. Generally, AAC blocks involve the use of aerated concrete which is made by introducing the air or other gas into a slurry composed of cement or lime and a siliceous filler so that when mixture sets hard after autoclaving, a uniform cellular structure is obtained. ACC blocks are steam cured for 14 to 18 hours during the manufacturing. If ACC blocks are manufactured in a faulty way, there are chances of occurrence of cracks in a wall, but as most of the manufacturer of AAC blocks are certified, so there are fewer chances of the bad quality of blocks. AAC blocks need to be tested in a certified lab before you construct a house. However, many manufacturers do not ensure proper steam curing while manufacturing the blocks in a factory, because of which sometimes shrinkage cracks may occur. Testing assures the quality of AAC block, whether they are good or bad. We always suggest people to use materials which are tested on site before they have been used for construction. 100 mm thick wall is generally used for the partition purpose. Even after the application of plaster, the wall can’t resist the continuous vibration or the frequent hit of a hammer which you do for nailing. It may also be a reason for cracks in the wall. It is therefore advisable to find the right cause of cracks so you can select the right method and materials to repair the cracks. We have already discussed the various reason which causes cracks in the wall.

Also Read: Reasons Behind Cracks in Plaster: An Incredibly Easy Guide

Repair of Cracks in AAC Block Wall

Repairing in a house is not an easy task. You have to take care while selecting the product as you are spending money for that. What is the meaning of spending money towards the repairing, if it is not going to be successful. It very important to read the product catalogue before you select the product. As they are non-structural cracks, what you need to do is simple fill with readymade crack filler material. You just have to make a paste and apply it like a putty. But please note that the cracks should not be wider than 2 to 3 mm in width. After selecting the right product, the next step is to prepare the surface for repairs. Remove the old putty. Clean the crack by applying edge of the knife. Use crack filler material like snowfilla of Snowcem brand, or other crack filler paint or putty like,

01. Asian Paint Smartcare Crack Seal:

It is used to seal the cracks up to the width of 3mm only. Read the product benefits, features, application procedure of Smartcare Crack Seal.

02. Dr.Fixit Crack X Paste:

It is used to seal the cracks up to the width of 5mm width only. You can apply this crack filler on a wet surface or some on a dry surface. The products are manufactured to satisfy the particular purpose of work. Hence read the product catalogue very carefully and use the product which is best suited to your situation. After the application, cure the repaired surface as specified in the product catalogue. After finishing the curing period, apply the putty and paint after one month. Use good quality plastic paint for painting the wall. Plastic paint has the ability to resist the further cracking of the wall up to some extent.