Mortars

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(§1) Mortar is the matrix used in the beds and the side joints of brickwork and for plastering walls and floors. Its functions are as follows:

1. To distribute the pressure throughout the brickwork;

2. To adhere and bind together the bricks;

3. To act as a non-conductor and prevent the transmission of heat, sound, and moisture from one side of wall to the other.

(§2) Mortar consists of an inert aggregate bound by a cementing material. The cementing material is most important in determining characteristics of the mortar. The usual cementing materials used for constructional work are hydraulic limes or Portland cement.

(§3) Clean, sharp pit sand is the best aggregate. Old bricks, burnt ballast or stones ground in a mortar mill may be used as substitutes for sand.

(§4) Mortars may be classified as follows:

a) cement mortars;

b) cement-lime mortars;

c) lime mortars.

(§5) Lime Mortar. This is a mixture of quick lime and sand in the proportion of 1 part lime to 2 or 3 parts sand in addition to water. It is the principal material used for bedding and jointing bricks, stones etc.

(§6) Non-hydraulic Lime Mortars must be well slaked before use. This type can be stored in a heap for several days after mixing. These mortars are not suitable for work below ground level, especially if the ground is water-logged.

(§7) Hydraulic Lime Mortars should be used within an hour after being mixed. Any mortar which has stiffened and cannot be knocked up by means of a trowel to a sufficiently plastic condition should never be used.

(§8) Cement Mortars. It is stronger than lime mortar and it is used in the construction of piers and load-bearing walls; it is also employed for work below ground level and for external walls. Cement Mortar is extensively used during winter, owing to its relatively quick-setting property.

(§9) Lime-Cement or Compo Mortars. Compo is a mixture of lime, cement and sand. It is usual to mix the lime mortar and then to gauge this mixture with the necessary proportion of Portland cement immediately before the mortar is required for use.

(§10) Cement Mortar produces the strongest brickwork; non-hydraulic lime mortar is approximately half the strength of that in cement mortar; hydraulic mortars are intermediate between that of cement and non-hydraulic lime mortars. The strength of compo mortars depend upon the cement content and may be very little less than that of cement mortar.

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