Sometimes you will find different type of cracks in a wall, which develop after a certain period of time. Cracks happen in both clay brick and AAC blocks walls. Sometimes a crack is observed after plastering. There is not a single reason for this occurrence, but by taking some precautionary measures, following certain guidelines and through proper workmanship these cracks can be eliminated or minimized.
Due to variable types of soil, differential settlement of a building may occur -- leading to large size cracks in the building and wall. For this purpose, proper investigation of soil is required before start of construction.
Trees or large plants growing close to the foundation may cause the soil toloosen and the load bearing capacity is compromised. Settlement cracks may occur over a period of time and endanger the building. Testing of soil should be done as deep as possible.
If blocks are not in one level, there are uneven stresses on the wall leading tocracks. For this purpose, First course of AAC blocks layers should be properly levelled using a 2 meter spirit level, and left for 24 hours for settling. And then the levelling of subsequent layers of blocks should be checked. Quality of workmanship is very important for crack prevention.
AAC blocks should have sufficient strength (≥ 3 N/mm2) as mentioned in construction standards with drying shrinkage within limit (< 0.1 %). Units should be free of cracks while in use and must be accurate in dimension within permissible limit. It is suggested to use mark AAC Blocks only. Quality of sand and cement is equally important and must be checked before use. For best results use Ready Mix Mortars.
Sometimes the beam above wall defects and imposes point loading on the wall and it may develop a crack. Care must be taken to avoid any possible deflection of the beam.
All building units have the tendency to shrink on drying and expand on wetting. For this purpose provision of control joints must be made in a wall.
Vertical Control Joints of 10 mm wide must be made in wall after 3 meters and filled with some resilient material or lean mortar to avoid possible crackage due to shrinkage expansion. SS Expansion ties and movement ties may be used at appropriate positions in wall as a prevention of crack control.
A reinforced bond beam must be made after every 1.2 meters in height and it should be discontinuous at control joints. The bond beam provides stability and strength and protects the wall for possible cracking.
All building units should be used at equilibrium moisture content to avoid moisture movement. For this purpose, sufficient time must be given, say 10 to 12 days after receipt of material at construction site.
Proper wetting of blocks should be done while jointing of blocks.
To avoid cracking in S-C plaster, do proper water curing for 7 days after drying of plaster. For an external wall, do plaster in two coats.
Concrete work in very hot and windy climate should be avoided, and in case if it is not avoidable then precaution shall be taken to keep the temperature of fresh concrete down and to prevent quick drying of concrete.
Reason and Prevention of Cracks in a Wall