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TO THE READER.
The well-merited celebrity and eminent character of NICHOLSON'S OPERATIVE MECHANIC AND BRITISH MACHINIST, are so fully established, that no commendation need be bestowed on a production which deservedly ranks as the first of all works hitherto published on the Literature of the Useful Arts : but as many divisions of that work, however interesting they may be to the general student, or important and useful to the intelligent Operative in their particular departments, may nevertheless possess only a secondary interest to persons not immediately engaged in those peculiar pursuits, the Proprietor of that work has printed the Section on BUILDING separately from the rest of the work, in order to furnish an invaluable manual to those engaged in the various occupations of that division of practical science, at a very moderate expence,
As a clear, concise and easy INTRODUCTION TO THE PRINCIPLES OF GEOMETRY AND MENSURATION is highly desirable to all persons engaged in Building, a few pages of APPENDIX are added, with the requisite explanatory Engravings, in order to furnish an interesting source of valuable instruction to the scientific mechanic, and to explain with great ease many useful problems, which will facilitate the comprehending a great number of important calculations and operations, which a long course of practical experience, unassisted by such help, might in vain endeavour to effect.
UNDER this general term, which implies the construction of an edifice according to the rules laid down by the different artificers employed, we purpose to treat of the respective business of the Mason, Bricklayer, Carpenter, Joiner, Plasterer, Plumber, Painter, and Glazier; previous to which it will be necessary to consider the sinking of the foundation, the due mixture of the ingredients which compose the mortar, and the art of making bricks ; upon the whole of which materially depends the stability of an edifice.
As firmness of foundation is indispensable, wherever it is intended to erect a building, the earth must be pierced by an iron bar, or struck with a rammer, and if found to shake, must be bored with a well-sinker's implement, in order to ascertain whether the shake be local or general. If the soil is in general good, the loose and soft parts, if not very deep, must be excavated until the labourers arrive at a solid bed capable of sustaining the pier or piers to be built. If not very loose, it may be made good by ramming into it very large stones, packed close together, and of a breadth proportionate to the intended weight of the building; but where very bad, it must be piled and planked.
In places where the soil is loose to any great depth, and over which it is intended to place apertures, such as doors, windows, &c. while the parts on which the piers are to stand are firm, the best plan is to turn an inverted arch under each intended aperture, as then the piers in sinking will carry with them the inverted arch, and by compressing the ground compel it to act against the under sides of the arch, which, if closely jointed, so far from yielding, will, with the abutting piers, operate as one solid body; but, on the contrary, if this expedient of the inverted arch is not adopted, the part of the wall under the aperture, being of less height, and consequently of less weight than the piers, will give way to the resistance of the soil acting on its base, and not only injure the brick-work between the apertures, but fracture the window-heads and cills.
In constructing so essential a part as the arch, great attention must be paid to its curvature, and we strongly recommend the parabolic curve to be adopted, as the most effectual for the purpose ; but if, in consequence of its depth, this cannot conveniently be introduced, the arch should never be made less than a semi-circle. The bed of the piers should be as uniform as possible, for, though the bottom of the trench be very firm, it will in some degree yield to the great weight that is upon it, and if the soil be softer in one part than in another, that part which is the softest, of course will yield more to the pressure,
and cause a fracture.
If the solid parts of the trench happen to be under the intended apertures, and the softer parts where piers are wanted, the reverse of the above practice must be resorted to; that is, the piers must be built on the firm parts, and have an arch that is not inverted between them. In performing this, attention must be paid to ascertain whether the pier will cover the arch; for if the middle of the pier rest over the middle of the summit of the arch, the narrower the pier is, the greater should be the curvature of the arch at its apex. When suspended arches are used, the intrados ought to be kept clear of the ground, that the arch may hove its due effect.
When the ground is in such a state as to require the foundation merely to be rammed, the stones are hammer-dressed, so as to be as little taper as possible, then laid of a breadth proportioned to the weight that is to be rested upon them, and afterwards well rammed together. In general, the lower bed of stones may be allowed to project about a foot from the face of the wall on each side, and on this bed another course may be laid to bring the bed of stones on a level with the top of the trench. The breadth of this upper
bed of stones should be four inches less than the lower one; that is, projecting about eight inches on either side of the wall. In all kinds of walling, each joint of every course must fall as nearly as possible in the centre, between two joints of the course immediately below it; for in all the various methods of laying stones or bricks, the principal aim is to procure the greatest lap on each other.
In making mortar, particular attention must be paid to the quality of the sand, and if it contain any proportion of clay or mud, or is brought from the sea-shore and contains saline particles, it must be washed in a stream of clear water till it be divested of its impurities. The necessity of the first has been clearly proved by Mr. Smeaton, who, in the course of a long and meritorious attention to his profession of an engineer, has found, that when mortar, though otherwise of the best quality, is mixed with a small proportion of unburnt clay, it never acquires that hardness which, without it, it would have attained ; and, with respect to the second, it is evident, that so long as the sand contains saline particles it cannot become hard and dry. The sharper and coarser the sand is the better for the mortar, and the less tlie quantity of lime to be used; and sand being the cheapest of the ingredients which compose the mortar, it is more profitable to the maker. The exact proportions of lime and sand are still undetermined ; but in general no more lime is required than is just sufficient to surround the particles of the sand, or sufficient to preserve the necessary degree of plasticity.
Mortar, in which sand forms the greater portion requires less water in its preparation, and consequently is sooner set. It is also harder and less liable to shrink in drying, because the limë, while drying, has a greater tendency to shrink than sand, which retains its original magnitude. The general proportions given by the London builders is lt cwt., or 37 bushels, of lime to 24 loads of sand; but if proper measures be taken to procure the best burnt lime and the best sand, and in tempering the materials, a greater portion of sand may be used. There is scarcely any mortar that has the lime well calcined, and the composition well beaten, but that will be found to-require two parts of sand to one part of unslacked lime; and it is worthy of observation, that the more the mortar is beaten the less proportion of lime suffices.
Many experiments have been made with a view to obtain the most useful proportion of the ingredients, and among the rest Dr. Higgins has given the following :
Lime newly slacked one part,
Coarse sand four parts. He also found that one-fourth of the lime of bone-ashes greatly improved the mortar, by giving it tenacity, and rendering it less liable to crack in the drying. It is best to slack the lime in small quantities as required for use, about a bushel at a time, in order to secure to the mortar such of its qualities as would evaporate were it allowed to remain slacked for a length of time. But if the inortar be slacked for any considerable time previous to being used, it should be kept covered up, and when wanted be re-beaten. If care be taken to secure it from the action of the atmosphere, it may thus remain covered up for a considerable period without its strength being in the least affected ; and, indeed, some advantages are gained, for it sets sooner, is less liable to crack in the drying, and is harder when dry.
Grout, which is a cement containing a larger proportion of water than the common mortar, is used to run into the narrow interstices and irregular courses of rubble-stone walls ; and as it is required to concrete in the course of a day, it'is composed of mortar that has been a long time made and thoroughly beaten.
Mortar, composed of pure lime, sand, and water, may be employed in the linings of reservoirs and aqueducts, provided a sufficient time is allowed for it to dry before the water is let in; but if a sufficient time is not allowed, and the water is admitted while the mortar is wet, it will soon fall to pieces. There are, however, certain ingredients which may be put into the common mortar to make it set immediately under the water ; or, if the quicklime composing the mortar contain in itself a certain portion of burnt clay, it will possess this property. For further information on this head the reader is referred to the sub-head-Plastering.
The earth best adapted for the manufacture of brick is of a clayey loam, neither containing too much argillaceous mat ter, which causes it to shrink in the drying, nor too much sand, which has a tendency to render the ware both heavy and brittle. It should be dug two or three years before it is wrought, that it may, by an exposure to the action of the atmosphere, lose the extraneous matter of which it is possessed when first drawn from its bed ; or, at least, should be allowed to remain one winter, that the frost may mellow and pulverize it sufficiently to facilitate the operation of tempering. As the quality of the brick is greatly dependent upon the tempering of the clay, great care should be taken to have this part of the process well done. Formerly the manner of performing it consisted in throwing the clay into