There are 4 primary reasons that cause defects in brick masonry work. These are as follows.
Crystallization of Salts from Bricks
Corrosion of Embedded Iron or Steel
Shrinkage on Drying
1. Sulphate Attack
The common forms of defects due to sulphate attack are
Chipping and spalling of bricks and
Formation of cracks in joints and rendering
These types of defects happens when sulphate salts present in brick work
react with alumina of cement in case of cement mortar or
react with hydraulic lime in case of lime mortar
This reaction causes increase in the volume of mortar and consequently leads to cracks, chipping and spalling of brick work.
These defects are commonly found in following situation;
exposed boundary wall
manhole and retaining walls (where they come in contact with moisture)
This type of defects can be prevented by adopting suitable construction detail and good quality materials that prohibits entry of moisture into the body of brick work.
2. Crystallization of Salts from Bricks
Defect formed due to crystallization of salts from brick are known as efflorescence.
Presence of excessive soluble salts in the brick is the primary cause of this type of defect. When these brick come in contact with water, the soluble salts present therein gets dissolved and comes to surface in the form of whitish powder.
Due to this defect the wall looks dull and losses it aesthetic look.
The only way to cure this defect is by repeatedly brushing and washing the wall surface.
3. Corrosion of Embedded Iron or Steel
Formation of cracks in brick work falls in this category.
Dampness in building causes corrosion of embedded iron or steel. Corrosion of steel results in increase in the volume of metal and thereby leads to crack in brick work.
The defect due to corrosion of steel or iron can be prevented by encasing the reinforcement in thick and impermeable cement mortar and providing a cover of 15 to 25 mm around the embedded member.
4. Shrinkage on Drying
Formation of cracks in masonry joints is one form of defect due to shrinkage.
As brick are porous material it has tendency to absorb water. When it absorbs water it swells and when this absorbed water evaporates brick starts to shrink. This shrinkage of brick creates cracks in brick masonry joints.
The formation and type of crack occurs is dependent upon type of mortar used in brick masonry. Where lean mortar is used in brick masonry crack get distributed over large number of joints and where thick mortar is used cracks are few but wider.
Shrinkage cracks do not affect the structural strength of brick work and it can be easily prevented