This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Lime Mortar. This mortar is prepared in much the same way as pure cement mortar. For mixing lime mortar, a bed of sand is first made in a mortar box, and the lime is distributed as evenly as possible over it, both the lime and sand being first measured in order that the proportion specified may be obtained.
The lime should then be slackd by pouring on water, and covered with a layer of sand, or, preferably, a tarpaulin, to retain the vapor given off while the lime is being slaked or converted into hydrates of lime by action of the water. Additional sand is then added if necessary, until the mortar contains the proper proportions. The proportion of sand to lime usually specified, and called for by the New York and Boston building laws, is 3 of sand to 1 of lime. If, however, both the materials are of good quality - that is, if the lime slakes freely, becomes a fine, impalpable powder, resembling flour in texture, and perfectly free from foreign matter, and the sand is clean and sharp - 1 part to 4 is sufficient; but more sand than this is injurious.
It is considered better to make lime mortar in large quantities; then to leave it in piles for use as it may be needed, after stirring and tempering.
Cement And Lime Mortar. For this mortar, the cement, lime, and sand should be well mixed together before water is added, as described for cement mortar. Cement and lime mortar should be used shortly after it has been mixed, before the cement sets.
Cement Mortar. This should be mixed in the proportion of from 3 to 4 parts of sand to 1 of cement. It is advisable that these parts should be actually measured in barrels, and the architect should see that this is done. (It is a common practice with many builders to have one laborer shovel cement or lime, while three or four of the strongest men are shoveling sand, it being called one of cement, to three or four of sand; this is a very unreliable method of measuring.) After the sand and cement are thrown on the platform, they must be thoroughly mixed by shoveling the two materials together, at least twice, so that the cement may be thoroughly incorporated with the sand. A little lime may be added in winter to prevent freezing. Sufficient water is now added to make a stiff paste, and the mortar must be immediately conveyed to the work and used, as the cement sets, or hardens, very rapidly, and after it is once hard the mortar cannot be used again.
There are two totally different architectural objects aimed at in using colored mortar; one is to get the effect of a mass of color by concealing the joints; the other is to use a contrasting color to emphasize the joints.
Common brick lose much of their rough effect when mortar of the same color as the brick is used, and the chipped or uneven edges do not show as plainly as they do when the bricks are laid in white mortar.
162. Most of the mortar colors and mineral pigments are sold either as a dry powder or in the form of a pulp or paste. Pulp colors seem to mix better with the mortar than dry colors, and are therefore preferable for the better class of work. Mortar colors, whether used in dry or pulp form, should never be mixed with lime until the lime has been slaked at least twenty-four hours. The color should, however, always be mixed very thoroughly with the lime putty before any sand is added; if the work is very fine, the colored mortar putty should be strained through a coarse sieve. When a quantity is required, the color should be mixed with the sand and set aside in barrels, and the cement added when required for use.
The colored mortar looks different in the bed than when dry. The final color can be seen by taking a little from the bed and permitting it to dry thoroughly.