To mix cement plaster, the cement, with or without 10% of lime, should be mixed thoroughly with sand until the colour is uniform. The water is then added gradually while mixing continues and until the required consistency is obtained or until it is just plastic enough to be spread and to hold to the building wall. It must be used within 45 minutes of mixing and no plaster that has begun to set should be remixed with water and used.

To mix cement-lime plaster, the cement, lime and sand may be mixed dry in the required proportions, then mixed wet with sufficient water to give the required consistency. With this method, the plaster must be used within 45 minutes of mixing and no re-tempering of partly set plaster should be attempted. More often, the lime and sand are mixed together first, to form what is known as the 'coarse stuff', this allows for further hydration of the lime before using and makes it easier to apply, more plastic and quicker setting. With this method mix 1 part of lime with 6 or 41/2 parts of sand (depending upon whether the mix is to be 1:1:6 or 1:2:9), first dry and then with sufficient water to give a stiff mix, adding the water gradually. The mortar should then be formed into a heap, covered with wet sacks and left for a week to 10 days. Then, immediately before use, the coarse stuff should be mixed with cement, using 1 part cement to 6 or 9 parts of coarse stuff, adding water if necessary to bring to a workable consistency, just right for plastering a building. After the cement is added the mortar must be used up within 45 minutes and no re-tempering of partly set mortar should be attempted.