Brick Masonry Walls

Construction of brick units bonded together with mortar (a mixture of cement/lime/mud and sand) is known as brick masonry. Bricks have been known to be part of wall construction since ancient times. The quality of bricks depends on the type of soil and the methods of production. There are two types of bricks burnt and unburnt. Unburnt bricks are the ones which can be produced in a small scale in formal units requiring less machinery and equipments with less capital. The only significant input is unskilled labour. Thus the cost of production relatively low. With mechanized production techniques, bricks with compressive strength upto 100 kg/cm2.

The Burnt bricks are mainly of three types i.e. country brick, the table moulded brick and wire cut brick. Country bricks are made by a single four sided mould. These bricks are moulded by the soft-mud process where soil is mixed with water and pressed. The moulding is done on level ground and the wet bricks is left on the ground to dry. After drying the bricks are stacked in a clamp and burnt using fossil fuel.

The Table moulded bricks are made of stiffer mud and use five sided mould. The use of lesser moisture during moulding leads to improved shape and strength for the brick. The wet brick is released by turning the mould upside down on a level platform. These bricks generally have a `frog' on one of the bedding faces. These bricks are then dried in shade and burnt in continuous kiln Bulls Trench Kiln. This kiln requires larger area of land and capital cost however this is the most popular form of brick production in northern part of India. These bricks are much stronger than country bricks with strength varying from 35kg/cm2 to 75kg/cm2.

The Wire cut bricks are produced by a more mechanised operation. The selected soil is pugged adequately and then extruded into a continuous slab of clay. This slab is then sliced by a wire frame into a number of bricks. After drying, the bricks are burnt in a Hoffmann's kiln. The strength of these bricks vary from 100kg/cm2 to 200kg/cm2. This is an expensive brick however can be used as cost effective option for load bearing construction upto five storeys in place of RCC framed construction. There are number of production units in NCR region.

It is interesting to note that the strength of bricks varies from region to region. The North Indian regions have brick strength 100kg/cm2 to 200kg/cm2 where as in South India the strength is below 100kg/cm2. However, the characteristic of wire cut bricks is somewhat same all over India.


230 mm thick brickwork with fps bricks in 1:6 cement mortar in English or Flemish bond		200 mm Thick Brickwork with Modular Bricks in 1:6 Cement Mortar in CBRI Bond
This walling system is very commonly used. Handmade and fired bricks of size about 224x114x70mm with a "frog" are used with 1:6 cement mortar to construct walls using the traditional Flemish or English bond. Handmade bricks have compressive strengths about 100 kg/cm2. Each course is about 75 mm and the wall thickness is 230 mm. Walls are finished with a 12 mm thick plaster on its smooth side and a 15 mm thick plaster on its rough side. Bricks are normally of two types one is traditional (fps) and modular. The fps bricks vary from 21 to 25cm in length, 10 to 13cm in width and 7.5cm in height in different parts of the country. The communally adopted nominal size of traditional brick is 23x11.4x76mm. With a view to achieve manufacture of uniform size of bricks all over the country, BIS has established standard size for brick. Such a brick is known as modular brick. The nominal size of this brick is 20x10x10cm where as the actual dimension are 19x9x9cm)		Modular bricks have a size of 190x90x90 mm. Thus, a brick wall constructed with this type of brick would conserve precious space when built and produce a lighter wall. The lighter wall will provide economy in foundation design. For every 300mm of wall height with modular bricks only three courses of mortar are used compared to four courses of mortar in the conventional fps brick. Thus, there is saving in mortar. Contrary to the accepted thinking that it involves less consumption of clay and coal, it has been recorded by manufacturers that these bricks require twice the normal level of fuel for firing evenly due to their bulk. For the purpose of this analysis, modular brick walls have been considered to have an exposed external face with pointing and 15mm thick plaster on the internal face.
190 mm Thick Brickwork with FBS Bricks in 1:6 Cement Mortar in CBRI Bonad		115 mm Thick waffle wall with FBS Bricks in 1:4 cement Mortar
Load bearing walls upto two storeys can be constructed with fps bricks to develop a wall 190mm thick. Parallel courses of brick are laid on their face as well as edge for a height of 230 mm. This forms one course in this case as far as breaking of joints or perpends within the wall is concerned. Corners and junctions are constructed to break the joint. The allowable basic stress for this wall is reduced to 85% on account of the reduced wall section. This system ensures saving on the material component. However, it is reported that there is no saving in the labour component as compared to the conventional brick wall. Both faces of the wall being smooth, the plaster thickness can be limited to 12mm on both faces.		In this system, sections of wall are made 115mm thick and interspersed with 230 x 230 mm bricks piers. The Piers act as stiffeners and the waffle shape adds stability to the wall. Due to its reduced wall cross section and the resultant slenderness ratio only double storeyed construction is possible with this walling system. The system has been used in housing projects by development authorities of UP.
230 mm Thick Brickwork with FBS BricksBricks I 2:2:12 Cement Lime Mortar
The rat-trap bond was invented and popularised the famous architect Laurie Baker. This system uses bricks-on-edge with a cavity behind every facer brick. Each course of brickwork is 115mm high, comprising of two parallel facers followed by brick placed at 90o to lock the bond. In the next course, the vertical mortar joints are broken by spanning the cavity at its centre with the locking brick. T and L junctions are made solid by filling the cavity with a brick-on-edge. Horizontal courses of brick-on-edge may be taken below the damp proof course (DPC), or at lintel and roof levels to provide horizontal tying. For every 230mm height of brickwork, there is a saving of one layer of mortar. It goes without saying that every three bricks laid saves one brick in this bond. This bond shows better performance against flexure as against the conventional brick wall. This is due to the fact that the through brick in this bond is laid on edge and hence action is against a 115mm depth instead of a 75mm depth. Thus, its overall performance is comparable to conventional bond work considering the cavity in the wall. For the system of external rendering the normal practice adopted is to keep the internal face of the wall smooth which can take a coat of 12mm plaster. The external header face is plastered so that the surface is finished in line with the stretcher face, which is left exposed. Thus the inner surface is protected from damp. (The brick work in rat-trap bond is a cost-effective option and is being used in several affordable housing projects by government and public agencies)
RAT TRAP BOND BRICK WALL
System Components	Initial Cost Structure	Design Example : Wall For A Two Storeyed Building With Rcc Roof
	Local Economy Component = 23% 23 mm thick load bearing wall in rat trap bond brick masonry using cement mortar (1:6) and class I bricks	Load on the Wall = 40KN Length of the Wall =3m One end continuous and the other end discontinuous Effective length = 0.9 x 3 = 2.7m (Table 5 : Section VI : 4 NBC) Thickness of the wall = 0.23m Effective thickness = 0.15m (Table 6 : Section VI : 4 NBC) Height of wall = 3m Effective height of wall = 0.75 x 3 = 2.25 (since roof is RCC) Area of cross section = 3 x 0.15 = 0.45 sqm Slenderness ratio = Min (2.25/.15,2/7/.15) = 15 Stress reduction factor = .78 (Table 8: Section VI : 4 NBC) Compressive stress = 44/.9 = 0.1 N/sqmm. Permissible compressive stress = 0.273 N/sqmm Hence Safe at 23 cm thickness
Critical Factors	Tools Used	DO'S	DON'T'S
1.Curing 2. Quality of Bricks 3. Not used for buildings having more than two floors 4. Quality of sand 5. Availability of skilled mason	1. Trowels 2. Plumb bob 3. Thread 4. Pans 5. Shovel 6. Baskets	1. Curing should be done for seven days 2. Cavity should be broken after six layers 3. Brick should be completely soaked in water before using for masonry 4. Mortar should be used within 30 minutes of adding water to the mix 5. Brick bats should be used at corners and T - Junctions	1. Find sand should not be used for masonry 2. Mortar should not be left in cavities
Construction Process

FLY-ASH BLOCK MASONRY
System Components	Initial Cost Structure	Critical Factors	Tools Used
		1.Curing 2. Placing the corner blocks at the corner and openings 3. Quality of sand 4. Availability of fly-ash near the block making site	1.Trowels 2.Plumb Bob 3. Thread 4. Pans 5. Showel 6. Baskets
DO'S		DON'T'S
1.Blocks should be cured for 14 days and the masonry for seven days 2. Vertical joints in masonry should be properly broken 3. Blocks should be well soaked in water before using for masonry 4. Mortar should be used within 30 minute of adding water in the mix.		1. Find sand should not be used for masonry 2. Masonry should not be allowed to dry quicklys
Construction Process
Take measured quantities of Fly-Ash, Lime and gypsum. Add water and mix thoroughly in the mixing machine	Take the mix out thoroughly mixing	Transfer the mix to moulding machine and compact	Place the wet blocks on open drying
Allow blocks to dry for 14 days	Tie the line and lay the first coarse of blocks	Lay the next course by breaking vertical Joint s	Apply cement mortar over the course
Check vertical levelusing plumb bob	Lay upper masonry after leaving openings for doorsand windows	Fill Mortar in the vertical joints	Apply mortar in the vertical joints and removing excess mortar
Pointing wall surface	A view of a Fly Ash block building