External plastering of buildings was at one time greatly in vogue in European countries, and there are many examples of "stucco"-covered buildings in the older portions of this country. Formerly lime and sand were used for the purpose, but this material is not very durable. If it is desired to plaster a brick building to imitate stone ashlar, Portland cement is the only material that should be used. It should be mixed with clean sharp sand, not too fine, in the proportion of 3 parts sand to 1 of cement. The wall to be covered should itself be dry, but the surface should be well wet down with a hose to prevent it from absorbing at once all the water in the cement; it should also be sufficiently rough to form a good key for the cement. Screeds may be formed on the surface, and the cement should be filled out the full thickness in one coat and of uniform substance throughout. When cement is put on in two or three coats, whether for exterior or interior work, the coats already applied should on no account be allowed to dry before the succeeding layers are added, otherwise they are quite sure to separate.
The manufacturers of Acme cement plaster claim that where brick buildings are to be plastered with cement on the outside, that their plaster is superior to Portland cement for the first coat, as it adheres more firmly to the brick, and will hold the Portland cement and the base upon which it is spread together.
The cement may be marked with lines to represent stone ashlar before it becomes hard. If it is desired to color the cement, mineral pigments must be used, such as Venetian red or the ochres. The natural color of the cement may be lightened by the addition of a very little lime.