HOW TO SUPERVISE BRICK MASONRY CONSTRUCTION ON SITE?

SUPERVISION OF BRICK WORK CONSTRUCTION

The following points should be kept in mind during supervision of brick work.

1. Before using the bricks in construction it should be checked for its physical properties (such as strength, dimension, water absorption etc).
2. Bricks must conform to the designer’s specification.
3. Prior to use bricks in construction, it should be soaked in water for sufficient time so that the water penetrates the whole depth of brick.
4. After completion of the soaking period, bricks should be removed from water and allowed to become surface dry, before use in construction.
5. Always laid the bricks having its frog facing upward.
6. The mortar should completely cover the bed and sides of the bricks.
7. During laying bricks on mortar bed, it should be slightly pressed into the mortar bed to ensure good bonding and uniform joint thickness.
8. During laying bricks should also be pressed sideways, to have uniform thickness of vertical joints.
9. All the joints in brick masonry should be so filled with mortar that no cavity is left in between.
10. Brick work construction should be started from its end or corners and it should be carried out perfectly in line.
11. The brick work should be perfectly in level.
12. Check the vertical faces of a brick work by means of a plumb bob and check the inclined surfaces by means of wooden templates.
13. Brick bonds as suggested by the designer should be adopted.
14. As far as possible try to use less no of brick bats.
15. Mortar of required consistency should be used.
16. The amount of mortar per use should be so prepared that it can be used within 30 minutes. Any mortar older than 30 minutes should not be used.
17. In case cross wall is to be inserted later, steps or toothing or recesses should be provided during construction.
18. At plinth, window sill, floor level, roof level and at the top of the parapet wall, the brick course should be laid with bricks on edge.
19. Iron fixtures such as hold fasts for doors & windows etc, should be embedded in cement mortar or cement concrete.
20. In case the wall face is to be plastered, all joints should be raked to a minimum depth of 10 to 15 mm. this raking is done when the mortar is in green condition.
21. If no plaster has to be done on wall surface, then joints in the wall surface should not be raked at all.
22. At every 30 m to 45 m length of wall, provide expansion joints of about 18 mm to 25 mm
23. After construction of brick masonry, it should be cured properly for a period of 1 to 2 week.

WHAT CAUSE DEFECTS IN BRICK MASONRY AND ITS REMEDIES?

SOURCES OF DEFECTS IN BRICK MASONRY

There are 4 primary reasons that cause defects in brick masonry work. These are as follows.

1. Sulphate Attack
2. Crystallization of Salts from Bricks
3. Corrosion of Embedded Iron or Steel
4. 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.

Spalling of brickwork

These defects are commonly found in following situation;

• exposed boundary wall
• parapet 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

Efflorescence of Brick

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.

Shrinkage crack in brick masonry

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

• by using good quality of brick and mortar
• by protecting masonry from moisture

HOW TO CLASSIFY WALLS IN A BUILDING? [BASED ON FUNCTION]

Walls are built to partition living area into different parts. They impart privacy and protection against temperature, rain and theft. Depending upon their functions, Walls may be classified into the following two primary classes

1. Load bearing walls
2. Partition walls.

1. LOAD BEARING WALLS

If beams and columns are not used, load from roof and floors are transferred to foundation by walls. Such walls are called load bearing walls. They are to be designed to transfer the load safely. The critical portion of the walls are near the openings of doors and windows and the positions where concrete beams rest.

Minimum wall thickness used is 200 mm. It is also recommended that the slenderness ratio of wall defined as ratio of effective length or effective height to thickness should not be more than 27. The effective height and effective length of a wall may be taken as shown in tables-1 and 2 respectively.

Table-1 [Effective height of walls in terms of actual height H]
End Condition	Effective Height
Lateral as well as rotational restraint	0.75 H
Lateral as well as rotational restraint at one end and only lateral restraint at other	0.85 H
Lateral restraint but no rotational restraint at both ends	1.0 H
Lateral and rotational restraint at one end and no restraint at other ends (compound walls, parapet walls etc.).	1.5 H

Table-2 [Effective length of walls of length L]
End Condition	Effective Length
Continuous and supported by cross walls	0.8 L
Continuous at one end and supported by cross walls at the other end	0.9 L
Wall supported by cross walls at each end	1.0 L
Free at one end and continuous at other end	1.5 L
Free at one end and supported by cross wall at other end	2.0 L

2. PARTITION WALLS

In framed structures partition walls are built to divide floor area for different utilities. They rest on floors. They do not carry loads from floor and roof. They have to carry only self-weight. Hence normally partition walls are thin. Table 8.4 shows the differences between load bearing walls and partition walls. Depending upon the requirement these walls may be brick partition, clay block partition, glass partition, wood partition, and aluminium and glass partition.

DIFFERENCES BETWEEN LOAD BEARING AND PARTITION WALLS

Differences between a load bearing wall and a partition wall is given in the following table

LOAD BEARING WALLS	PARTITION WALLS
They carry loads from roof, floor, self-weight etc.	They carry self-weight only.
They are thick and hence occupy more floor area.	These walls are thin and hence occupy less floor area.
As the material required is more the construction cost is more.	As the material required is less, construction cost is less.
Stones or bricks are used for the construction	Stones are generally not used for the construction

source:- www.civilblog.org