The correct method of measuring the different aggregates of concrete or cement mortar is to weigh them. But this is not possible at most sites. The common way is to measure the volume. Although this is not a precise method, it is efficient enough if performed carefully. Measuring by the shovelful is not acceptable since this is too inaccurate. Measuring must be done with buckets or wooden boxes, all of equal size. A 1:3 mixture means three measurements of sifted sand to one measurement of cement. These two dry components have to be mixed (see Fig. 3.4) by shovelling a pile of sand with the required amount of cement added from one side of the mixing platform to the other and then back. This procedure has to be repeated 4-6 times until the dry mixture is of equal colour. Before adding water, prepare another pile of dry mixture. A second pile of dry mixture should always be ready before water is added to the first pile. This gives a certain guarantee that there will be no interruption of the supply of mortar for the plasterers.

Water must be added very carefully. It is appropriate to make a test of a small amount first and let the plasterer try to work it. The mortar for ferro-cement must be moist, not wet. If you can take it in your hand and shape a ball without water running through your fingers, this indicates the right consistency. Water should never be visible in the mixture and the mortar should not look shiny. For waterproof plaster on bricktanks, the mortar is slightly wetter, but here, as with ferro-cement, the same problem occurs if too much water is added. In this case the mortar slides on the underground where it settles and horizontal cracks appear. The cracks indicate that the mortar is no longer homogeneous. Work should stop until proper mortar is supplied. The content of water in the mixture is a most sensitive issue. It is called water-cement ratio. For easy understanding it should be realized that where water is, no other material can be. But since water will eventually run off, it will contain cement. The structure will be weakened if too much water is added. It can be said that only 10% more water than necessary to make the plaster workable will reduce the strength of the plaster by 15%. If 50% more water is added, the plaster will lose 50% of its strength. The same applies for concrete, although it can be observed everywhere that concrete is considered to be good and workable if it runs out of the wheelbarrow. This consistency is wrong and creates a weaker concrete.