There can be many defects in bricks. Identifying defective bricks is important for the consideration of stability and durability of load bearing brick masonry walls and structures.
Types of Defects in Bricks and their IdentificationFollowing are the different types of defects generally found in bricks:
1. Over burning of bricksWhen bricks over-burn, soft molten mass is produced and the brick will its shape along with other designated requirements.
2. 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.
- Consequently, bricks with low compressive strength and high-water absorption will be produced.
- They produce a dull sound when struck against each other.
- Finally, such bricks are not recommended for construction works
3. Bloating of bricksBloating 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.
4. Black coreImproper 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.
5. EfflorescencePresence 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. Lastly, efflorescence can be minimized by selecting proper clay materials for brick manufacturing, preventing moisture to come in contact with the masonry, by providing waterproof coping and by using water repellent materials in mortar and by providing damp proof course.
6. Brick cracking
Straight cracksStraight 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.
- 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.
- additionally, the presence of pebbles in clay mix could lead to random cracking as well.
7. Brick spalling
- Irregular portion of the brick break away of fall off.
- Heating of water inside brick is the cause of spalling
8. ChuffsThe deformation of the shape of bricks due to rain water falling on hot bricks is known as chuffs.
- Disintegration of bricks is the indicator of lime blowing.
- If bricks contain lime lump, then lime blowing is expected. The lime absorb 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.
- It is a dark spot on brick surface.
- The presence of iron sulphide in clay brick is the main cause of spots.
- Bricks with sports on its surface is unsuitable for exposed masonry work.
11. 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.
12. Defects in brick size
- Brick oversize in width, length, and thickness
- Size defects make bricks lighter than normal bricks
- Oversize in all three dimensions of bricks might cause by under-firing, poor material selection and preparation. For example, presence of too much sand that decline among of drying.
- Oversize in width and length occur due to brick squashing while it is still wet. This may have been occurred when the brick was set down on the ground or drying rack after being molded or when a slop molded brick was pressed to flatten out a distortion.
- Oversize in thickness, which is common problem in wire cut bricks, occurs during brick wire cutting. the block of clay is forced through a row of wires. As a result, the force on the wire may cause movement that changes the dimension of the opening which the clay passes through.
- This problem occurs due to several factors for example, faulty mould, presence of too much clay in the batch, using too much water during the mixing stage, and over firing.
13. Defects in brick shape
Slump brick shape
- It occurs when clay mix is considerably wet, so it slumps under its weight.
Rounded corner brick
- Corner breakage between drying and firing may cause this problem.
- Another factor is that, the worker does not push clay into the mould properly.
Lip on bed face
- Excessive clay is not removed from the face of the brick during manufacturing is the cause of presence of lip on brick bed face.
- Leaving flashing around brick top edge border during production process is another factor that led to this issue.
Banana brick shape
- It occurs when the brick is not turned around during initial drying phase prior to the hardening of top face.
Contaminated or distorted of brick under face
- Surface on which bricks are dried is either uneven or dirty of combination thereof.
- Frequently, it occurs with slope moulding as wetter mixture picks up more particles.
Stacking marks on bricks
- Bricks distort
- Bricks get finger marks or other marks
- Moving bricks from individual drying to stack drying before it is dried adequately is the cause of stacking marks.
Brick multiple distortions
- It loses its shape and suffer different distortions at the same time.
- Brick forming may be the cause of multiple distortions.
- Lastly, brick over-burn at the base of the clamp cause multiple distortions as well.