Bond is the arrangement of bricks in the wall so that the vertical joints do not form a continuous straight line. To maintain strength the bricks must be lapped over each other both along the courses and through the thickness of the wall. In housing, cavity walls are now always used and they are formed with bricks laid lengthwise along the wall so that the wall is 112.5 mm or half-brick thick. This is called stretcher bond. The bond is achieved by starting alternate courses with a half brick. This half brick is formed by the return brick at corners,, or by cutting a brick in half at the end of a straight wall, or at an opening. Where two walls join, the bond has to be maintained and some cutting has to be undertaken. Pieces of brick are called bats and for bonding at the junction of a half-brick wall two ¾ bats will be needed at alternate courses.
The two leaves of a cavity wall are held together with metal ties made of galvanised metal and shaped to form a drip at their centres, so that moisture will drip down to the bottom of the cavity and escape through the weep holes provided at the base of the wall. They are spaced at 900 mm centres horizontally and 300 mm centres vertically and are also staggered so that they do not form vertical rows.
When 225 mm walls are being built, the bonding pattern becomes more complicated and there are a number of patterns from which to choose. The strongest bond is called English and consists of a course of stretcher bricks followed by a course of headers. These are bricks that are laid at right angles so that their ends show at the face of the wall. In order to stagger the vertical joints to provide the bond a brick cut lengthwise has to be placed after the first header of each heading course. This cut brick is known as a Queen Closer. Closers are bricks which are cut along their length.
Junctions of walls which are built in English bond are not complicated, but they must be carried out correctly or continuous vertical joints will occur in the centre of the wall. They may not be obvious when looking at the face of the brickwork, but they will weaken the structure.
Another bond which is not often used now is Flemish. This is simpy courses of one stretcher brick followed by one header along the length of the wall. The header must be in the centre of the stretcher of the course above and below and to achieve this a queen closer has to be placed after the first header of successive courses. This bond is weaker than English bond because a straight vertical joint occurs inside the centre of the wall on each side of the headers.
A variation of English bond, which is more often used, is garden wall bond. This is three courses of stretchers followed by one of headers. Some straight vertical joints occur inside the wall but they are not detrimental. The number of stretcher courses can be increased for simple garden walls where no specific strength is required. It is not usual to exceed six courses of stretchers between the courses of headers. Flemish garden wall bond consists of three stretchers followed by a header throughout each course. A queen closer occurs after the first header in alternate courses.
Gate posts and free-standing piers must be large enough to withstand the strain that will be placed on them; bonding is not their only requirement, as they must have sufficient sectional area or they will break apart at the bed joints, especially at the point where the crook of a hinge is built-in. The minimum size for the average gate is not less than 330 mm, that is V/1 brick square, but a two-brick square pillar 450 mm square is better and more able to withstand the vibrations of the slamming gate. A coping or cap should always be provided to protect the top of the brickwork and make the rainwater drip clear.
Bricks are cut to the various shapes which are required, by means of a bricklayer’s bolster chisel which is like a cold chisel but has a thin blade two to four inches wide and a small club hammer. Final trimming to shape is done with the chisel end of the brick hammer.
Blockwork construction techniques
Concrete and insulating blocks are made in larger sizes than bricks, the average size being 457 mm X 228 mm and thicknesses are from 50 mm upward. The insulating blocks used for the inner leaf of a cavity wall are 100 mm thick and the dimensions must allow each course of blocks to be level with a course of bricks on the outer leaf of the wall. There are usually three courses of bricks to each course of blocks.
This also applies to the blocks used for partition walls inside the building, as these walls are bonded into the inner leaf of the cavity walls whether or not they are bricks or blocks. The method used to bond blocks to a brick wall is to set alternate courses into the brickwork and when the outer walls are being built, holes are left in the brickwork at the appropriate positions so that the internal walls can be bonded-in later. Sometimes, stone-faced decorative blocks are used for the outer leaf of cvity walls and these decorative blocks may be of regular size or in random sizes, but whichever type is used they must be made to course up with the inner leaf at regular intervals so that the wall-ties can be inserted in their proper places. These bonding patterns apply to all internal brick or block walls whether load-bearing or non-load-bearing.
Laying the Bricks and Blocks
The art of bricklaying can only be acquired by practice. First, the materials must be prepared properly and placed in convenient positions. The board for the mortar must be reached easily and long walls require a number of boards positioned at intervals which will allow the bricklayer to move along the wall and always be within easy reach of a board full of mortar. Bricks must be stacked in similar convenient positions just an arm’s reach from the face of the wall, so that no unnecessary movement is involved. The mortar board is set on a brick at each corner so that it is clear of the ground and the surface of the board and the mortar will be kept clean.
Grasp the trowel firmly with the thumb on the ferrule so that a flexible wrist action is possible. A banana-shaped quantity of mortar is cut out of the heap and picked up on the trowel with an easy sweeping action and is spread on to the wall. Do not make the mistake of laying too thick a bed of mortar as it will only be squeezed out when the brick or block is tapped down to the guide line, with the result that the face of the wall will be stained and the excess mortar will have to be collected on the trowel before it can run further down the wall. With a little practice it should not prove difficult to gauge roughly the right quantity of mortar needed.
The hollow frog of the brick is laid upward, but if hand-made bricks are being laid and they are bent in their length, as they may well be, because this is part of their charm, lay them with their hollow side down, especially where they are used as headers in one-brick or more thick walls.
Engineering bricks are difficult to lay and are not the right type to learn with. Because they are non-absorbent, they tend to ‘swim’ about in the mortar. This makes it hard to keep them in line with the face of the wall and progress is very slow unless a great deal of skill at bricklaying has been acquired.
In summer, ordinary bricks will need wetting to clear off the dust and to reduce the natural suction of the clay. Engineering bricks do not need this treatment of course. At the end of the work the top of the wall must be covered with sacks in the winter to prevent frost damage and the scaffold boards next to the wall should be turned on edge to prevent rain splashing off it and staining the face of the brickwork.
Brickwork starts by building-up the corners or ends of the walls. A string-line is set up on the profiles to mark the position of the face of the brickwork. Then mortar is spread on the concrete foundation. A long spirit level is used to plumb down from the string-line and a trowel mark is made to indicate the position of the corner brick.
Three or four more bricks are then laid in each direction, each one being carefully plumbed into position. A straight edge is used to test the front face of the bricks to ensure that as well as being plumb down from the line, they are also in line with each other. Each brick is also levelled on the top surface and again when three or four bricks have been laid they are levelled with the straight edge. Each brick has a small amount of mortar placed on the end to form the vertical or perpendicular joint. These perpends must be fully filled with mortar and not left half empty with just enough mortar at the face to form a pointing finish.
When four or five bricks have been laid on the foundation concrete, the second course of bricks can be laid. The process is exactly the same except that the first brick is laid on the opposite side of the corner, so that a bond is formed by the overlapping bricks.
When the first corner has been raised five or six courses, work can start on the second corner. Plumbing and levelling must be carried out meticulously as the corner brickwork will be used as a guide for the rest of the wall. The common way of holding the string-line for the wall is to wrap it around metal line-pins which have a flat blade that can be pushed into the mortar joints. A better way, which is needed when the mortar has set hard, is to make a pair of line blocks, which are L-shaped pieces of wood with a slot cut in one side for the line to pass through and a couple more to hold the line tight.
The line is fixed so that it is right on the top corner of the brick. When laying bricks to the line always ensure that a trace of daylight can be seen between the brick and the line. This prevents bricks being laid hard against the line, pushing it forward and eventually putting the whole wall out of alignment. One other tool is essential for good brickwork, and that is a gauge rod. This is a length of timber on which the courses of brickwork are clearly marked. As the corners are built up the rod is tried against them and the courses brought in line with the marks on the rod. By this means each corner is kept the same height and has the same number of courses, because the gauge rod ensures that the mortar joints are the same thickness. If a gauge rod is not used it is possible for the corners to be brought up to the same height, but because of thick mortar joints one could have a course of brick less than the other which would make it impossible for a string-line to be used for lining up the wall between the corners. Building is continued in this manner until all the walls are up to the required height.