FOUNDATION, CONCRETE.
In walling, the bedding joints have most commonly an hori zontal position in the face of the work, and this disposition ought always to take place when the top of the wall termi nates in an horizontal plane or line. In bridge building, and in the masonry of fence-walls upon inclined surfitces, the bed ding-joints on the face sometimes follow the upper surface of the wall or terminating line.
The footings of stone-walls ought to be constructed of large stones, which, if not naturally nearly square, should be reduced by the hammer to that form, and to an equal thickness in the same course ; for if the beds of the stones in the foundation taper, the superstructure will be: apt to give way, by resting upon mere angles or points with inclined beds instead of horizontal. All the vertical joints of any upper course should break joint, that is, they should fall upon the solid part of the stones in the lower course, and not upon the joints.
When the walls of the superstructure are thin, the stones which compose the inundation may be so disposed, that their length may reach across each course, from one side of the wall to the other. In thicker walls, where the difficulty is greater in procuring stones of sufficient length to reach across the foundation, every second stone in the course may be a whole stone in the breadth, and each interval may consist of two stones of equal breadth, that is, placing header and stretcher alternately. But when those stones cannot be had conveniently, from one side of the wall, lay a header and stretcher alternately, and from the other side lay another series of stone in the same manner, so that the length of each header may be two-thirds, and the breadth of each stretcher one-third of the breadth of the wall, and so that the back of' each header may come in contact with the back of an opposite stretcher, and the side of that header come in contact with the side of the header adjoining the said stretcher. In broad foundations, where stones cannot be procured for a length equal to two-thirds of the breadth of the foundation, build the work so that the upright joints of any course may fall on the middle of the length of the stones in the course below, and so that the backs of each stone in any course may fall upon the solid of a stone or stones in the course below.
The foundation should consist of several courses, of which each superior course should be of less breadth than the infe rior one, say four inches on each side in ordinary cases, and the upper course project four inches on each side of the wall. The number of courses must be regulated by the weight of the wall, and by the size of the stones of which the founda tion consists.
A wall, which is built of unhe•n stone, is called a rubble wall, whether with or without mortar. Rubble work is of too kinds, coursed and uncoursed. Coursed rubble is that of which the stones arc gauged and dressed by the hammer, and thrown into different heaps, each heap containing stones of the same thickness ; then the masonry is laid in courses or horizontal rows, which may be of different thicknesses. The uncoursed rubble is that where the stones are laid pro miscuously in the wall, without any attention to placing them in rows. The only preparation which the stones undergo, is that of knocking of the sharp angles with the thick end of the scabbling hammer.
Walls are most commonly built with an ashlar facing, and backed with brick or rubble work. Brick backings are com mon in London, where brick is cheaper ; and stone backing in the north of England and in Scotland, where stone is pleu tiful. Walls faced with ashlar, and backed with brick or unconrsed rubble, are liable to become convex on the outside from the greater number of joints, and from the greater quantity of mortar placed in each joint, as the shrinking of the mortar will be in proportion to the quantity.; and there fore a wall of this description is much inferior to one of which the facing and backing are of the same kind, and built with equal care, even though both sides were uncoursed rubble, \vhich is the worst of all walling. Where the outside of a wall is an ashlar facing, and the inside coursed rubble, the courses of the backing should be as high as possible, and set with thin beds of mortar. In Scotland, where stone abounds, and where perhaps as good ashlar facings are constructed as any in Great Britain, the backing of their walls most monly consists or uncoursed rubble, built with very little care. In the north of England, where the ashlar facings of walls are done with less neatness, they are much more particular in the coursing of their backings. Coursed rubble and brick backings arc favourable for the insert; ri of bond timbers : but in good masonry, wooden bonds should never be in con tinued lengths, as in case of fire or rot, the wood will perish, and the masonry, being reduced by the breadth of the tim ben, will he liable to bend at the place where it is inserted. When it is necessary to have wall timber for the fastening of battens far lath and plaster, the pieces of timber ought to be built with the fibres of the wood perpendicular to the surfitee of the wall, or otherwise in unconnected short pieces, not exceeding nine inches in length.