The object aimed at in using colored mortars is either to get the effect of a mass of color, by concealing the joints, or else, by using a contrasting color, to emphasize the joints. Rougher bricks may also be used with nearly as good effect by using a mortar of the same color as the bricks. Chipped or uneven edges do not show as plainly with mortar of the same color as the bricks as they do when laid with white mortar.
Objections to Mortar Colors. - The objection is sometimes made to the use of colored mortars that they are not as strong as white mortars and that the color is very apt to fade.
These objections undoubtedly have much truth in them when cheap colors are used and the mortar is not properly mixed, but it is very doubtful if the better grades of mortar colors now on the market affect the strength of the mortar to any appreciable extent, and when properly mixed with lime putty they seldom, if ever, fade.
Most, if not all, of the coloring materials sold under the name of "mortar colors," or stains, consist of mineral pigments put up either in the form of a dry powder or in the form of a pulp or paste.
Pulp colors are said to be susceptible of more uniform mixing with the mortar than dry colors, and, as a rule, appear to have the preference for the better grades of work.
Paste or pulp stains should not be allowed to freeze, and should be kept moist by covering with water.
A great deal of colored mortar is made by using Venetian red, or the cheap grades of mineral paints for the coloring matter. The ordinary Venetian red is very apt to fade and also weakens the mortar, and the cheaper grades of mineral colors are not much better. The cost of the coloring matter is so small an item that only the very best grades should be used.
Among the brands of mortar colors generally recognized as belonging to the first grade are the "Clinton," "Peerless," "Peoria," "Edinburgh," "American Seal," "Milwaukee" and "Cabot."
The principal colors used are red, brown, buff and black, although green, purple, gray and drab mortar colors are also made.
Mortar colors, whether in dry or paste form, should not be mixed with lime until the latter has been slaked at least twenty-four hours, and the best way is to keep a lot of lime putty on hand and mix the color with it as needed.
The color should be thoroughly and evenly mixed with the putty before the sand is added, and for very fine work the colored putty should be strained through a coarse sieve.
For cement work the stain should be thoroughly mixed with the sand or gravel and set aside in barrels, and the cement added in small quantities as required for use.
Like all water paints, the color of the mortar looks different in the bed than when dry. To get the final color of the mortar a little should be taken from the bed and permitted to dry thoroughly, when the permanent color may be seen.
The amount of coloring matter required to stain a given quantity of mortar varies with the different colors and brands. The following quantities may be taken as the average amounts required in laying one thousand face brick :
Red or terra cotta, 50 pounds.
Buff, brown or French gray, 25 pounds.
Black, 22 pounds.