Cement mortar is mixed by hand for small construction purposes, while large quantities of cement mortar may be mixed by a machine.
1. Hand Mixing
Sand is measured in boxes, and the specified quantity of sand is spread first. Cement is measured by the weight of bags or by considering the volume of 0.035 m3. Cement is spread over the sand. Then they are dry mixed by turning over and over and backward and forward using a shovel or a spade till the mixture attains a uniform colour.
The quantity of mix that has to be used within 30 minutes is separated and mixed again and formed into a heap. After making a small depression at the top, water is added to the centre of the depression and mixed well. Adequate water must be added, as excess water may draw the cement out. The water required is roughly about 70% of the weight of cement for 1:3 mortar. The whole mass is mixed thoroughly for 10–15 minutes by hand mixing.
2. Machine Mixing
Machine mixing of cement mortar is done in a concrete mixer. The sand and then the cement are put into the mixer. Initially, it is dry mixed and then water is gradually added. Wet mixing is then continued for more than a minute till the mixture is brought to a plastic consistency.
Cement mortar has to be used before it begins to set. The entire cement mortar has to be used within a maximum time of 2 hours. While using the cement mortar, water may be added to the mortar when the mortar gets stiffened. This process may be continued to restore the necessary consistency. Such retempering may be allowed only up to a period of 2 hours, beyond which the mortar should not be used.
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