cement bricks

cement brick

The proportions of cement, lime and sand to use depend upon the purpose of the plaster and the nature of the building surface to which it is to be applied. A pure lime plaster is comparatively soft and weak and is slow setting, so it is usually gauged with cement to increase its strength and hardness and to shorten the period of hardening. The strength increases and the period of hardening decreases as the amount of cement increases in proportion to the amount of lime, until with a pure cement plaster with no lime, the strength is a maximum and the hardening period the least. However, as the proportion of cement is increased the plaster becomes less workable and more difficult to apply. The proportion of sand should not exceed three times the combined proportions of lime and cement. A stronger plaster should not be applied to weak porous backing or a strong finish coat to a weak first coat.