Mastic was first introduced from France by Hamlin. but is now sold only by Messrs. Francis and White, :it Nine Elms. it is composed of pounded stone, silver sand, lithatre. and red lead, and, when manufactured, has the appearance of very fine sand. The manner of working Mastic is entirely different from that of Roman cement.
To one ewt. of Mastic add one gallon of linseed-oil, and let well incorporated by the labourer, which must be effected by treading them together with the feet until the amalgamation is complete, which may be easily ascertained by smoothing a portion of the mixture with the shovel : should any bright spots be observable, the must lie again and again repeated until they completely disappear, when it is considered fit for use.
The manner in which Mastic is used is as follows :—The joints of the brickwork being \Yell cleaned out, the work must he correctly plumbed up by means of flat-headed nails. and screeds, for the ellidanee of the floating-rule, thrilled with Roman cement, and kept about one inch in breadth. This done, the bricks must be well saturated with boiled lin seed-oil of the best qnality. and the Mastic laid on with the hands. assisted occasionally by the laying-trowel, until the space between the screeds be covered to the thickness required. The floating-rule is then passed carefully over the work ; and when the space between the screeds is sufli eientiy filled up, it must be floated with a hand-float. com posed of sycamore or beech, until it assumes the same aprearanee as highly-polished stone. Thus a space of large dimensions must be folowed up until the whole is completed, when the screeds Twist be cut out. their places filled with Mastic, and compactly hand-floated into the rest of the work.
Within the last few years various compositions have been for the co% ening of the exterior of Stich as Roman Cement, Terra Cotta. Bailey's Composition, and a host or others, all more or less patronized the public.
It would be impossible for us to give descriptions of all these compositions; but we shall shortly explain the mode aprepa•ing and using the Roman cement. This cement,
finniliarly known among plasterers as Comp°, was first intro duced to public notice by Messrs. Parker and Wyatt, who took out a patent for it, and who succeeded in obtaining for it an extensive sale.
It is prepared from the kind of stone called clay-balls, or septaria, by being. after a manner of mantifitcturing plaster, first broken into pieces of a convenient size, slowly calcined in kilns or ovens, and afterwards ground to a fine powder, and put into proper casks, great care being taken to preserve it from damp. Two parts of this composition. with three parts of clean grit-sand, will form a very durable substitute fir stone. in selecting the sand, great care must be taken to procure it free from clay or mud, and of a sharp and bind ing quality. or it must be washed until perfectly clean.
This composition, when it is intended to compo, as it is termed, the exterior of a building, is thus used : After the walls have been well soaked with water, the cement must be prepare] by the hawke-boy on a stiff board made for the purpose, adding as witch water as brings it to the consistency of paste, but no more must be mixed than can be used in ten minutes. It must be laid on with the greatest possible expedition, in one coat of three-quarters of an inch in thickness, and after being well-adjusted with the floating-rule-, the hand-float must lie incessantly used to bring it to a firm and solid surthce before it sets, which it does in about fifteen minutes.
The work should then be drawn and jointed to imitate well-bonded masonry, and afterwards coloured with a wash composed of live ounces of copperas to every gallon of water —a sufficient quantity of fresh lime and cement—and to the whole adding the colours necessary to imitate any particular stone that may be required.
Terra Cotta, or artificial stone, is an excellent and durable composition, advantageously used at the present day for all kinds of exterior decoration. It is a compound of pipe-clay, stone-bottles, glass, and flint, well pounded together, and sifted through a fine sieve, a small portion of silver-sand afterwards added.