5.4 Masonry and mortar

The mortar and bricks should have about the same strenght. If the bricks are soft, the mortar must also not be too hard. If a good brick is thrown on to the ground three metres away, it must not break. If the bricks are of poor quality, the walls must be thicker. Mortar consists of sand, water and the binders. Cement gives a solid, watertight mortar. Cement mortar is brittle in masonry construction. Lime gives a soft, sticky mortar.

For masonry construction, cement mortar should always include a certain amount of lime. This makes it more workable, and the masonry becomes more watertight.

Mixing ratio:

Masonry mortar	2 (cement)	: 1 (lime)
		: 10(sand)
or	1 (cement)	: 6 (sand)
Rendering mortar	1 (cement)	: 4 (sand)
better	1 (cement)	: 3 (sand)

The most important part of the mortar is the sand. It must be clean. It should not contain any loam, dust or organic matter. Mortar sand with a high proportion of dust or loam "eats up" much more cement than clean sand.

Fig. 22: Testing of mortar sand 1. Fines (loam, dust): Water glass 1/3 sand, 2/3 water. stir vigorously. Leave to stand for one hour. Measure fines. A maximum of 10 % of the amount of sand is permissible. 2. Organic matter: Bottle with stopper (not cork) to be filled with 1/3 sand and 2/3 soda lye (3 %). Shake repeatedly within an hour. Leave to stand for 24 hours. Water colour clear or light yellow: good; red or brown: bad.

The bricklayer or works foreman must check the sand before use (Figure 22). Sand may contain not more than 10% dust or loam, otherwise it must be washed. Soda Iye can be used to test whether the sand contains excessive organic matter. The following points are important when rendering:

- The rendering mortar must be compressed by vigorous, circular rubbing.
- All edges must be rounded.
- All internal angles must be rounded with a glass bottle.