2G0 COTTAGE, FARM, AND VILLA ARCHITECTURE. kinds common in Britain, Parker's and Mulgrave's ; the Puzzolano ; the tarras ; the gypsum ; the mastic ; Frost's cement ; the metallic cement ; and Bailey's composition. The first two, and the gypsum, possess in an eminent degree the power of setting almost instantaneously, either with or without an admixture of sand. Puzzolano earth, tarras, and Frost's cement are better calculated than the Roman cements to indurate with lime ; because they do not set so quickly. A very hard and durable cement may be formed of stone lime recently burned, and, immediately after being slacked, mixed with clean, sharp sand. This about London is called Bailey's composition, and is packed dry in casks, and sent to any distance. The usual proportions are, three of sand to one of lime. Mastic is a calcareous cement, which consists of earth, and other substances almost insoluble in water, to which, when pulverised, are added any of the oxides of lead, and also a quantity of glass, or flint stones ; the whole reduced to a fine powder, and intimately incorporated with any cheap vegetable oil. This is rather too expensive a cement for cottages ; but it forms a better imitation of stone, especially of freestone, than any other, and has this great advantage over all the others, that, when put up into casks, it will keep without injury for any length of time. In general, wherever good fresh lime and clean sharp sand can be had, an excellent cement may be formed. Mr. Frost has proved that lime, even chalk-lime, burned in a close kiln, and cooled without coming in the slightest degree in contact with the atmosphere, will, when afterwards slacked, and mixed with sharp sand, set as rapidly as Roman cement, and this even under water. ( See the Spe- cification, of the Patent in the Repertory of Arts.) In England, the scrapings of the public roads, where limestone or sandstone is the material employed, are found to serve as a substitute for sharp sand, provided care be taken (o wash from them their finer earthy particles. But on the subject of cements we shall enter more at length in a future part of this work. 528. The object of coverinff the outside of the walls of cottages ivith cement is generally to imitate stone. In this imitation, care must be taken that the lines drawn do not represent stones of too large a size ; that the shapes of the stones at the corners, and for the lintels and sills of doors and windows, be suited to their situations and uses ; and that, in the regular courses, the joints alternate and show bond properly, as in regularly built stone buildings. A dwelling with the walls of brick will often be much improved in appearance by forming the string courses, the facings or architraves to the doors and windows, the corner stones, the cornices, the tablings, and especially the chimney-tops, of cement in imitation of stone. Where the cement used for either of these purposes is lime and sand, it will resemble stone with little or no colouring matter added ; but where Roman cement, or Puzzolano, or tarras, is used, the colour, after being laid on, will be dark, and the cement must therefore be brought to a stone colour by washing it over with washes, composed in proportions of five ounces of copperas to every gallon of water, and as much fresh lime and cement (to which some add tallow), as will produce the colour required. The copperas, or sulphate of iron, oxidises with the atmosphere, and produces a reddish tinge. The forms of the stones, defined by the lines, should, some days afterwards, be touched with umber, ochres of different shades, and occasionally with vitriol ; which colours, if laid on by a painter who knows how to imitate tlie tints of nature, will produce a harmonious effect. Oil colours should not be used on cement laid on walls in the open air for a year or more, till the water mixed up with it is either solidified or evaporated. When cement is once thoroughly dry, its hardness and durabi- lity is greatly increased by washing it over with any oily or greasy matter, with or with- out a mixture of colour incorporated. There are various litliic paints for covering cement, all of which are composed of oxide of lead, powdered glass or other vitrified matter, and the colour of the stone to be imitated, intimately mixed together, and beaten up with oil. 529. Roughcasting, or Harling as it is called in Scotland, is a mode of outside finish- ing well calculated to protect walls from the weather. It is not capable of such a high degree of beauty as a covering of cement, because a roughcast wall is only a plastered wall with a rough surface, instead of a smooth one ; but then it is considerably cheaper than any description of stucco. It is much used for covering rubble stone walls and houses, in Scotland and Ireland. The following is the process : — Plaster the wall over with lime and hair-mortar ; when this is dry, add another coat of the same material, laid on as smoothly and evenly as possible. As fast as this coat is finished, a second workman follows the other, with a pail of roughcast, which he throws on the new plas- tering. The materials for roughcasting are composed of fine gravel, reduced to a uniform size by sifting or screening, and with the earth washed cleanly out of it ; this gravel is then mixed with pure newly slacked lime and water, till the whole is of the consistence of a semi-fluid : it is then forcibly thrown, or rather splashed, upon the wall with a large trowel, which the plasterer holds in his right hand, while in his left he has a common whitewash brush. With the former he dashes on the roughcast, and with the latter.
