The important causes responsible for cracks in building are :
1. Due to movement of ground.
2. Due to temperature variation.
3. Due to moisture changes.
4. Due to effect of chemical reaction.
5. Due to creep and elastic deformation.
6. Due to vegetation.
1. Due to movement of ground:
a) If the building is erected on or near an area which is likely to be subjected to mining substance landslides, earthquake etc. the movement of ground due to this factors can cause cracks in building.
b) Building constructed on shrinkable soils are liable to crack due to volumetric change in subsoil conditions due to change in moisture content, unless special measures are taken.
2. Due to temperature variation:
a) In some materials the changes in temperature can cause appreciable change in their size the extent of movement due to temperature variation in the building components depends upon number of factors such as dimension of materials, its coefficient of expansion.
b) In case of roof slab supported on load bearing walls, cracks occur due to temperature variation. The roof slab being exposed to the heat of sun, is subjected to alternate expansion and contraction. This movement of slab may result in pushing out top course of masonry and developing horizontal cracks in supporting walls.
3. Due to moisture change:
a) Most of the building materials like bricks, concrete, mortar, stones, timber etc. have pores hence these materials increases in size or expand on absorbing moisture and decrease in size or shrink on drying.
b) Shrinkage on account of drying out of moisture contents in building material is one of the main factor responsible for cracks in the building.
4. Due to effect of chemical reaction:
a) The carbon dioxide present in the air reacts chemically with cement based product, resulting in increase in volume which ultimately leads to cracking.
b) Soluble sulphates which may be present in the soil, ground water or clay bricks react chemically with Portland cement in presence of water and cause the concrete or mortar joint or brick itself to expand considerably leading to the formation of cracks.
5. Due to creep and elastic deformation:
a) The different components of building like wall, column, beam etc. undergo elastic deformation when loaded.
b) The situation where cracking due to elastic deformation and creep arise are summarized as a cracks in masonry when a wall is unevenly loaded, cracks in masonry due to deflection of RCC beam or slab , cracks at a function of brick masonry with RCC column in load bearing walls.
6. Due to vegetation :
a) The effect of existence of vegetation near the building becomes more damaging when the soil at site is of shrinkable type.
b) The roots of growing trees causes drying and shrinkage of the subsoil and this can result in unequal settlement of the foundation leading to cracks.
Measure adopted to prevent the cracks:
1. Building should be well designed.
2. Proper curing should be done.
3. Continuous vertical joint in wall should be avoided by proper band.
4. Use of low quality material should be avoided.
5. There should be good workmanship.
6. Uneven settlement of foundation should be avoided by resting foundation on hard strata.