This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The proportion of sand used in mortar should vary with the kind of cement and the use for which the work is intended. With Rosendale cement, the proportion of sand should not exceed three to one, and for piers two to one. Portland cement may contain sand in proportion of four to one, and lime mortar three to one. The object of using sand in mortar is to prevent too much shrinkage, and as a cheaper material than lime or cement, its functions being mechanical rather than chemical. It strengthens lime mortar, by supplying a base to which the particles of lime adhere more firmly than to each other, but its presence in cement mortar is a weakness. In all eases a thorough mixing is essential, the object being to so thoroughly mix the particles that no two grains of sand shall lie against each other without a film of cement between. The cement and sand should be mixed dry, the process being to spread them in layers and then turn and work the mass until it is thoroughly mixed,
Fig. 118, Stone Skewback.
HOUSE AT CANTON, ILL.
R. C. Spencer, Jr., Architect, Chicago, Ill.
If too much sand is added the mortar will stick to the trowel and will not work easily. The superintendent should become, as soon as possible, familiar with the appearance of good mortar so that he can tell readily whether too much or too little sand has been added. If the mortar slides easily from the trowel it is usually of the right proportion. In ordinary practice, the lime and sand are mixed as soon as the lime is slaked and allowed to stand until needed, but it is better not to mix the sand until ready for use. Coarse sand makes a stronger mortar than fine sand, and a fine, loamy sand, although it works easier than sharp coarse sand, does not make a strong mortar.