Types of Defects in Bricks and their Identification
Following are the different types of defects generally found in bricks:
Sulphate Attack
The common forms of defects due to sulfate attack are
- Chipping and spalling of bricks and
- Formation of cracks in joints and rendering
These types of defects happen when sulphate salts present in brickwork react with alumina of cement in case of cement mortar or react with hydraulic lime in case of lime mortar.
This reaction causes an increase in the volume of mortar and consequently leads to cracks, chipping and spalling of brickwork.
These defects are commonly found in the following situation; exposed boundary wall parapet wall manhole and retaining walls (where they meet moisture)
This type of defects can be prevented by adopting suitable construction detail and good quality materials that prohibit the entry of moisture into the body of brickwork.
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Crystallization of Salts from Bricks
Efflorescence of Brick- Defects found on bricks.
Defect formed due to the crystallization of salts from brick is known as efflorescence.
The presence of excessive soluble salts in the brick is the primary cause of this type of defect. When these bricks meet water, the soluble salts present therein gets dissolved and comes to the 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.
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Corrosion of Embedded Iron or Steel
The 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 an 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.
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Shrinkage on Drying
The formation of cracks in masonry joints is one form of defect due to shrinkage.
As brick is a porous material it has a 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 that occur are dependent upon the type of mortar used in brick masonry. Where lean mortar is used in brick masonry cracks get distributed over a large number of joints and where thick mortar is used cracks are few but wider.
Shrinkage cracks do not affect the structural strength of brickwork and they can be easily prevented
- by using good quality of brick and mortar
by protecting masonry from moisture
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Over Burning of Bricks
When bricks over-burn, soft molten mass is produced, and the brick will its shape along with other designated requirements.
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Under Burning of Bricks
When bricks are not burnt to cause complete vitrification, the clay is not softened because of insufficient heat and the pores are not closed.
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Bloating of Bricks
Bloating of bricks is spongy swollen mass over the surface of burned bricks. Presence of excess carbonaceous matter and Sulphur in brick-clay is the main cause of bloating.
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Black Core
Improper burning is the prime cause of brick black core. Bricks, which contains bituminous matter or carbon and they are not completely removed by oxidation, will commonly experience such problem.
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Efflorescence
The presence of drying grey or white powder patches on the brick surface is the efflorescence indicator. This defect is caused because of alkalis present in bricks. When bricks come in contact with moisture, water is absorbed and the alkalis crystalize.
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Brick Cracking
Straight Cracks
Straight cracks at right angles from one of the long surfaces of the brick will develop. Considerably rapid drying is the cause of straight cracks. Possibly, brick damage occurs even if fired adequately.
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Random Cracks
Cracks initiate arbitrarily on different brick surfaces.
Differential drying generate shrinkage. then, various lumps of dried materials will shrinkage differently which eventually lead to random cracking.
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Brick Spalling
The irregular portion of the brick breaks away or falls off.
The heating of water inside brick is the cause of spalling.
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Chuffs
The deformation of the shape of bricks due to rain water falling on hot bricks is known as chuffs.
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Lime Blowing
The disintegration of bricks is the indicator of lime blowing.
If bricks contain lime lump, then lime blowing is expected. The lime absorbs water and expand after its exposure to firing. Consequently, lime blowing will take place.
Bricks susceptible to lime blowing can be identified by submerging the brick in water. As a result, the brick fractures and powdery lumps will be exposed.
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Spots
It is a dark spot on the brick surface.
The presence of iron sulphide in clay brick is the main cause of spots.
Bricks with sports on their surface are unsuitable for exposed masonry work.
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Lamination Bricks
Thin lamina produces on the brick faces which weather out on exposure.
Entrapped air in the voids of clay is the cause of laminations.
Such bricks are weak in structure.
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Lecture on Defects in Bricks
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About the Author
This article is written by Engr. Ibrar Khan.
Who is a Civil Engineer by Profession.
(c) Some Rights Reserved.
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