MASONRY, the art of preparing stones, so as to tooth or indent them into each other, and form regular surfaces, either for shelter, convenience, or defence: as the habitations of men, animals, the protection and shelter of goods, &c.
The chief stone used in London is Portland, which comes from the island of Portland, in Dorsetshire. It is used for public edifices, not only in ornaments, mouldings, and strings, but in all the exterior parts. In private buildings, where brickwork predominates, it is used in strings, window-sills, balusters, steps, copings, &c. It must be observed, however, that under a great pressure it is apt to splinter or flush at the joints, and fin. this reason the joints cannot be made so close as many other kinds of stones will admit of. When it is recently quarried it is soft, and works easily, but acquires great hardness in length of time. The cathedral of St. Paul, Westminster-bridge, and almost every public edifice in London, are constructed wholly, or in part, of Portland stone.
Purbeck stone comes from the island of Purbeck, in Dor setshire also. It is mostly employed in rough work, as steps and paving.
stone is also used where strength and durability are requisite, as in paving and coping. Ryegate stone is used fbr hearths, slabs. and copings.
In Edinburgh, a very fine stone, called Craigleith, brought from a village of the same name, in the neighbourhood of that city, is most commonly used in the construction of edifices. They have also very good stone from the Hails quarry, but rather inferior in point of colour.
The Craigleith quarry produces two kinds of rock, one of a fine cream or butt colour, called the liver rock, which is almost unchangeable, even though exposed in a building to the weather.
The city of Glasgow is built of various kinds of stone, the best of which are the Posse] and the Lord President's quarry ; most other kinds are not only perishable, but liable to change their colour.
the north of England, stone fit for hewn work is chiefly of a reddish colour. There is a very good white stone, how ever, in the vicinity of Liverpool, of which several of the public buildings are constructed.
All the stone fit to be squared, or squared and rubbed smooth, for the use of building, is mostly composed of sand. The stone used for the same purposes in the south of England is, in some parts, entirely chalk, and in other parts limestone. The Bath and Oxfbrdshire stone has so little grit in its tex ture, as to be wrought into mouldings with planes, as in joinery, and the surfaces are finished with an instrument called a dray.
Marbles, with regard to their contexture and variegation of colour, are almost of infinite variety some arc black, some white, some of a dove colour, and others beautifully variegated with every kind of rich colour. The best kind of
white marble is that called statuary, which, when cut into thin slices, becomes almost transparent, a property the others do not possess. The texture of marble, with regard to work ing, is not generally understood, even by the best workmen, though upon sight they frequently know whether it will receive a polish or not. Some marbles are easily wrought, some are very hard, and other kinds resist the tools alto gether.
Mortar is another principal material used in cementing the stones of a building. The reader who wishes to obtain a full knowledge of this department of masonry, may consult the articles CEMENT, MORTAR.
Wherever it is intended to build upon, the ground must be tried with an iron crow, or with a hammer : if' found to shake, it must be pierced with a borer, such as is used by well-dig gers; and it' the ground generally prove to be firm, the loose or soft parts, if not very deep, must be excavated until a solid bed appears.
If the ground prove soft in several places to a great depth under apertures, and firm upon the site of the piers, inverted arches must be turned under the apertures, so that if the foundation sink, the arches may resist the re-action of the ground : and then the whole wall will sink uniformly, or descend in one body. And even where the ground is of a uniform texture, it is always eligible to turn inverted arches under apertures, wherever there is a part of a wall carried up from the fbundation to the sill of that aperture : it is from neglect in this circumstance, that the sills of windows in the gronnd-stories of buildings are frequently broken ; indeed it is seldom or never otherwise.
Arches adequate to this purpose should rather be of a para bolic form than circular, the figure of the parabola being better adapted to preserve an equilibrium than the arc of a circle, which is of uniform curvature. If unfortunately the soft parts of the ground prove to be the site of the piers, and, consequently, the hard places under the apertures, piers should be built under the apertures, and arches suspended between the piers, with their concave side towards the trench, as usual.
The use of concrete has, however, made a great change in the art of preparing foundations, the general practice now being to excavate the trenches for the footings of the walls, and put in a bed of concrete, on which is laid the masonry. For more information upon this subject, see the articles