The Useful Arts Employed in the Construction of Dwelling Houses. Second Edition

The material mainly employed in the construction of buildings depends partly on the purpose for which the buildings are intended, and still more, perhaps, on the prevailing geological character of the surrounding country. In such a place as London, where there is an immense mass of tenacious clay beneath the vegetable soil, and where solid stone is not to be had, except by bringing it, at a great expense, from a distance of many miles, clay seems to be the natural material for dwellings; and thus we find that almost all the London houses are built of brick formed of clay. In other parts of Great Britain, such as Glasgow or Edinburgh, the case is very different; for, in those places, clay is scarce, and stone is plentiful. There are quarries not far from Edinburgh, and others within the very precincts of Glasgow, where an abundant supply of good building-stone is obtained at a very low rate. Hence it follows as a natural consequence, that the houses in those two cities exhibit a large proportion of stone structures; so much so, indeed, that an inhabitant of London, who is accustomed to see stone appropriated only to large important public buildings, is apt to imagine that the houses in the two northern cities must necessarily be very costly. This is by no means certain, however, for the builders in each city make use of those materials which may be most available.

Whether stone form the main portion of the walls of a house, as in the cases just named, or whether it is only used in smaller degree, as in London houses, the operations by which it is worked and fitted are pretty much the same; and we will therefore devote this chapter to a brief description of the principal kinds of building-stone, followed by an outline of the Mason’s operations.

Principal Varieties of Building-stone.

Granites are rocks which have been formed by the union of three different minerals in a state of fusion; these, on cooling, have crystallized and become distinct from each other in the mass. It is on the varied proportions in which these three constituents are combined, that the colour, hardness, durability, and beauty of the various granites depend. The light-red and rose-coloured granites contain the felspar in greatest abundance and in the largest crystals; but this mineral varies in hue from the purest white to nearly black; it is the ingredient most acted on by the atmosphere; the rock, therefore, which abounds in it, though it may be more beautiful to the eye, and more easily worked at first, is not so durable as that which contains it in smaller crystals, and with a larger proportion of quartz. It is to this last-named mineral that granite owes the sparkling appearance which it presents when the sun shines on it; quartz is the hardest and most imperishable of the three minerals which form the granite-rock. The third, mica, is distinguishable from the other two by its satiny, shining, dark hue, and is very apparent in the coarse-grained, handsome stone of our own country, brought from Cornwall.

When the felspar is replaced by another mineral called hornblende, the stone is of a dark-greenish hue, and the component parts are in a finer form and less distinguishable from each other. The Aberdeen granite is an example of this kind, which is more durable than the former, though not so pleasing to the eye.

Granite occurs in all the larger mountain-ranges, and in isolated masses in every country; not being a stratified rock, and being excessively hard, it is difficult to quarry and get out in manageable masses. Blasting with gunpowder is the mode usually employed in this country; the pieces detached by this means are hewn roughly into form on the spot by a small pickaxe. Aberdeen granite is quarried by cutting a deep line some yards long, and placing strong iron wedges at equal distances in this line; these wedges are struck in succession by heavy hammers till the mass splits down. This, or analogous modes, may always be employed when the rock approaches a slaty or stratified structure, as is the case with some nearly related to granite. Another method of detaching masses of rock, is by driving wooden wedges into a deep fissure, either natural or artificial; the wedges are then wetted, and the consequent expansion of the wood bursts the rock asunder.

As granite has always to be brought from a great distance to the spot where it is wanted, because its natural localities are far from the places where edifices are usually constructed, and also on account of its hardness, this rock is only used for important buildings, such as bridges, markets, churches, &c., and not commonly even for these. London and Waterloo bridges, Covent Garden and Hungerford markets, and the York column in Pall Mall, are instances of its use in London.

The principal kinds of stone used in building are the LIMESTONES, or calcareous rocks of the geologist; of these it would be useless to describe or enumerate more than a few. In our own country, the Portland stone, so called from its principal quarries being in Portland Island, in Dorsetshire, holds the first rank, and is that almost exclusively used in London for building, and for the ornamental parts of edifices. It unites the qualities of being easily sawn and worked, when lately quarried, and of subsequently hardening by exposure to the air; it is close and even in its texture, admitting of being wrought into delicate work, and receiving a very smooth surface, which it will retain for a considerable period, though it is surpassed in durability by many other rocks. It is said that the Banquetting-house, Whitehall, was the first building in London in which this stone was employed. St. Paul’s, Westminster and Blackfriars’ bridges, Newgate, and, indeed, most of the public buildings of the metropolis, are examples of its use.