Basics in Building Construction

Basics in Building Construction 4(2+2)

Lesson 10 : Brick Masonry

Principles Of Brick Masonry Construction

The strength of masonry work, however, depends very much upon the type of material used, nature of workmanship and supervision. Bad workmanship assisted by lack of supervision may lead to unsound construction inspite of the materials used being of the best possible type. The general principles which should be observed for a sound brick masonry construction are:

1. The bricks used in a good work should be sound, hard and well burnt with uniform size, shape and colour. They should have no cracks or flaws and a fractured surface should be free from holes, grit or lumps of lime etc. The surface, of the bricks should be such that no mark should be made when scratched by the finger nail. The bricks when struck together should produce metallic ringing sound and they should not break when dropped from a height of 90 to 120 cm. on the ground. The bricks should not as a rule absorbs water more than 20% of their dry weight when immersed in water for twenty – four hours.
2. The bricks should be thoroughly soaked in clear water before use for suitable period so that the water just penetrates the full depth of bricks. This not only helps in removing the dirt, dust and other soluble salts (which cause efflorescence) from the bricks, but also reduces their tendency of suction of water from wet mortar.
3. The bricks should be laid on a full bed of mortar. They should be slightly pressed into the bed mortar while laying so as to ensure proper adhesion. All the courses should be laid horizontal and all vertical joints should be vertical.
4. All the joints should be properly flushed and filled with mortar so that no cavity is left in between.
5. In case of walls two brick or more in thickness, the joints should be grouted at every course in addition to bedding and flushing with mortar.
6. No brick-bats should be used in the work except when it is absolutely necessary for obtaining the specified bond.
7. Brick work is generally laid in the English bond. In all cases, it should be ensured that a proper bond is maintained throughout the work.
8. Only specified mortar of a good quality should be used in the work, taking great care that uniform mortar joint is obtained throughout the construction. Thickness of joints should not exceed 13 mm in any case.
9. Unless brick-on-edge is specified, the bricks must be laid on their proper beds with their frogs pointing upwards.
10. The courses of bricks at the plinth, window sill, floor/roof level and at the top of parapet wall should invariably be laid with brick on edge.
11. The progress of work in raising masonry should be such that all the connected brick work should be carried up in uniform layers at one level.
12. The buttresses, counterforts etc. should be built up course by course, maintaining proper bond with the main wall and should not be added or joggled afterwards.
13. Iron fixtures like pipes, hold-fasts of doors and windows etc. which are to be fixed in the bricks wall should be embedded in cement mortar or in cement concrete.
14. The face joints are generally raked to a minimum depth of 10-15 mm. when the mortar in the joints is still green. This is done to provide proper key for the plastering or pointing.
15. Plastering should be done after about 28 days of completion of brick masonry. This permits adequate time for the shrinkage in masonry and concrete to take place before plastering operation is carried out.
16. In works where plastering or pointing is not desired, the mortar joints should be struck flush and finished at the time of laying.
17. All the finished masonry work should be kept wet for at least seven days.
18. When an existing wall has to be strengthened by making it thicker, 20 cm. x 20 cm. x 10cm. (dimensions of one brick) recesses are cut in the existing wall. The recesses are staggered taking care that one recess is made in every square meter of the wall. This enables the new work to be properly bonded to the old one. This operation is termed as back-bonding.
19. When it is desired to increase the length of the wall under construction at a future date, the wall is stopped with a toothed end. This is necessary to ensure continuous bonding between the old and the new work.
20. It is found that with an average winter-summer temperature differences of about 100o F a brick masonry wall expands by about 10 mm. in every 30m. length of wall. Hence it is desirable to provide minimum 18 mm. wide expansion joints after every 30 to 45 mm. length of wall.
21. When the timber floor or roof is required to be supported on masonry walls, the ends of timber joists (supporting the floor or roof) should rest on corbels or brackets as far as possible. In cases where the ends of timber joists have to be built into the wall itself, it is necessary to apply suitable preservative treatment to the embedded portion of the joists and in addition some space should be left around them to minimize chances of attack by termite and to ensure free circulation of air.
22. Bed blocks of stone, concrete or reinforced concrete should be provided at the ends of beam carrying heavy loads.
23. The bearing of R.C.C. floor or roof slab resting on brick masonry walls should not be less than effective depth of slab or 10 cm. whichever is more.
24. As a general practice, quoin brick should be headers and stretchers laid in alternate courses and the bond is developed by placing a quoin closer next to the queen header.
25. Half brick partition walls should be reinforced with suitable reinforcement placed at every third or fourth course of the brick work. The reinforcement may be in the form of mild steel bars, flat bars, hoops iron, expanded mesh, or steel fabric etc.