Mortar, a preparation of lime and sand, mixed with water: it serves as a cement, and is employ ed by masons and bricklayers In erecting walls, houses, etc. Mortar being an article of extensive utility, it becomes an object of considerable importance to discover such a method of preparing it, together with such materials, as will perfectly cohere, and at the same time resist the action of the weather.
Having already treated, at some length, on this subject, under the head of Cement, we shall at present state two of the most simple methods of preparing strong and durable mortar.
The proportions of lime and sand usually employed in making the common mortar, are two parts of the former to three of the latter, which are mixed up with soft water ; but its quality and durability will, according to Dr. Anderson, be considerably improved, if the lime be slaked, and the sand mixed up with lime-water, instead of the common. The reason assigned for this opinion is, that the fluid drawn from weds contains a large portion of fixed air ; which, by mingling with the mortar before it is used, reduces the quick-lime into a kind of inert calcareous earth, similar to chalk, and thus spoils the cement. But, if the mortar be worked up in a perfectly caustic state, it attracts, the air so slowly, that it concretes into a kind of stony matter, which, in the course of time, becomes as hard as the rock from which the lime-stone was taken.
In the year 1777 was published (in French),an ingenious"Inquiry concerning the Manner in which the Romans prepared the Lime they used in Bui/ding ; as also on their method of mixing and using their Mortar;" by M. DE: LaPaye.— The principal circumstance appears to be the mode of slaking the lime without liquefying it, so as to reduce it to powder; and at the same time to leave it sufficiently caustic to yield a strong mortar; which, in proportion to its age, will acquire additional strength.-To effect such object, it is requisite to select good fresh lime, made of hard line-stone, which is to be broken into pieces of the size of an egg. These should be placed in a shallow open basket, which ought to be plunged into water, till the surface of the fluid begin to boil. The basket is then drawn out, and suffered to drain for a short time; after which the lime is put into casks, where it speedily grows hot, and crumbles into powder.
The lime thus prepared, is to be mixed with various compositions of mortar, according to the purposes for which they are designed. It may be preserved for a considerable time, and will retain its useful properties, by simply covering the casks with straw.- M. Guy-ton states, in a late volume of the Annales de Chimie, that he employed this lime, 18 years since, in the construction of a small aqueduct, which was intended to convey water to an artificial nitre-bed. The mortar consisted of equal parts of the following three ingredients, namely, sand, fragments of cal-careous stone, and lime slaked according to the directions above given : in a short time, it acquired an uncommon degree of firmness, which has re- mained unimpaired since that period.- See also BuiLD-ing, vol. i. p. 382.