This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
1. It unites the bricks together by its adhesion to their surfaces, thus causing the whole of a structure to act as a homogeneous mass.
2. It distributes the pressure evenly over the united surfaces of the bricks by filling up all the irregularities of these surfaces.
3. It fills up the joints of the brickwork, and thus prevents the penetration of moisture and the passage of the air, and so prevents any excessive changes of temperature within.
A clause very frequently introduced into a Specification is that no four courses of bricks together with four mortar joints shall measure more than one inch in excess of four courses of the bricks laid dry. This means that the average thickness of the mortar joints is 1/4 inch. It is obvious, however, that the thickness of the joint depends in great measure upon the regularity of the surfaces of the bricks. With common bricks it is usually essential to have joints at least 1/4 inch thick, in order that there may be a cushion of mortar between every part of the surfaces united; while with bricks of better quality the joints may be less, even down to 1/32 inch for carefully gauged work.
The most usual methods of laying bricks, especially in walls of no great thickness, is that known as Shoving, which is performed in the following manner: -
- A bed of mortar is spread with a trowel over the course of bricks last laid, and the quoin brick is carefully laid in position. The vertical edges which come on the face and end of the wall are buttered - that is to say, mortar is scraped on to these edges with a trowel, so that when the adjoining bricks are placed in position the vertical joints will be thoroughly filled with mortar at the outside ends. The adjoining bricks are next shoved into position with a downward sloping motion towards the quoin brick, so that the mortar oozes up into the vertical joints. It is then tapped with the handle of the trowel, and thus moved slightly in one direction or another until it exactly occupies the desired position, with its face vertical and flush with the surface of the wall, the mortar which oozes out of the joints on the face of the wall being scraped off with a trowel and thrown on to the interior of the wall. The next facing bricks are then laid, and the operation is continued until two or three feet of facings have been laid. The bricks on the interior of the wall are now laid, being shoved with a diagonal sloping motion against the facings and the last brick laid, this being necessary with the interior bricks so as to cause the mortar to ooze up into the vertical joint on two or three sides as the case may be.
Grouting is a process used when a fine joint is required, as in rubbed or gauged work. The bricks are laid in position on a bed of fine mortar, with the external edges of the facing bricks buttered. The interior bricks are then filled in, and the vertical joints are filled up with grout, i.e. mortar watered down to the consistency of cream and poured in from a can.
Grouting should never be used when the joints to be filled are large, as in that case there is a tendency for the sand to sink to the bottom of the joint.
In thick walls the most economical way of building is by a method called Larrying. In this the face bricks are first laid by the shoving method, the mortar being spread by means of a trowel. Hods or barrow loads of fairly liquid mortar are then tipped on to the interior of the wall and spread in a fairly thick even layer by means of a larry (see Fig. 174), and the interior bricks are shoved into position as already explained.
Bricks should always be wetted before laying, for two reasons: - 1. To remove any dust from their surfaces. 2. To prevent them from absorbing the water from the mortar.
If there is any dust on the surfaces of the bricks the mortar will not adhere to them, and thus the strength of the work is considerably impaired.
If the water is absorbed from mortar it will not set properly, and it will crumble away.
If possible the wetting process should be performed by soaking the bricks in water, in a tub, for the space of 24 hours. Ample provision should be made, as bricks will absorb about one-sixth their weight of water, which is equivalent to one pint of water per brick, or 550 gallons per rod of brickwork. Less water is required when the bricks are sprinkled with a hose or dipped in a bucket, and generally a bricklayer has a bucket of water by his side when at work, in which he immerses the bricks for a short time before setting them in the work.
It is very important that brickwork should be protected from the effects of the weather. It is better in frosty weather to suspend the work altogether, as the water contained in the mortar freezes and expands, thus weakening the work. There is danger, too, of a frozen wall buckling should the sun shine upon and thaw the ice in the joints on one face. Should it be necessary to continue the work in cold weather it should be done during the intervals between the frosts, and it should be covered with straw or sacks whenever the thermometer falls below freezing-point. When brickwork is built in Portland cement it may be continued in during a frost, as the cement sets before the water has time to freeze. If the wall is built in lime mortar the addition of about one-fifth of its bulk of quick-setting lime will enable the work to be carried on without danger with the thermometer well below freezing-point.
Rain and sleet without frost will not injure brickwork, but are actually a great advantage, as they thoroughly wet the bricks; but the tops of walls must be covered over with weather boards to prevent the water from running down the face of the work and discolouring it.