A seventh sort of work is seen in the ancient walls of Naples, where two outside walls are built of squared stones laid in regular courses, PP, Fig. 12, bound to gether by transverse or cross walls at certain distances, as QQ, and having the remaining spaces between these walls filled up with stones and earth.
The ancients bestowed great pains upon forming the beds and joints of the stones ; they were frequently so fine as to escape the eye. They usually worked only at first the bed and joints, and having set the stones in this state, afterwards polished the faces.
Palladio directs, that as the wall rises above the ground, its thickness should diminish in the manner of a pyra mid ; that the inside face of the wall should be in a per pendicular line; that the thickness of the podium or foot of the wall, be half that of the foundation ; in the mid dle of the wall, or front band, the thickness be diminished half a brick ; at the top, or crown of the building, ano ther half brick to be taken away ; and that some sculp ture, or bas relief, should conceal outwardly the gradual diminution. That great attention should be paid to ren der the angles as firm as possible by means of long and hard stones ; and that the openings, windows, &c. be removed, at least to the distance of their own breadth from the angles.
In modern house building, the bedding joints of the squared stones or bricks have always a horizontal posi tion. In piers, quays, and bridges, the bedding joints are generally laid at a right angle with the latter of the outside faces ; and these latter are sometimes worked iu the reticulated manner, that is, the courses are laid at an angle of 45° with the horizon. But this subject will be more fully discussed under the article MASONRY.
The footings in the foundations of stone walls should be composed of large square stones, all of the same course, being of an equal thickness. If the foundations are made to taper much, the superstructure will depend on the back parts of the lowermost stones, and unlcis these are very truly worked and laid, it will therefore be liable to give way. Where the direction of a wall is up the face of steep ground, cut into steps, the footings must be bedded with great care ; and all the upright joints of an upper footing stone, should break joint, or fall upon the middle of the stones below. In laying the founda
tions of thin walls, where stones of proper size can be had, each course of the looting should consist of stones reaching the entire thickness of the walls, with the pro per projections. But in thicker walls, when only a part of the stones can be had of sufficient length, then every alternate stone may be laid quite across the wall ; the in terval consisting of two stones in breadth, after the man ner of Flemish bond in brickwork. If even these bond stones cannot be procured, then every alternate stone may be in length two thirds of the thickness on one side the wall, and on the other side a stone of one third of the same breadth may be placed, and the order reversed in the next course, which will form a sufficiently strong bond. In broader foundations, where stones cannot be procured equal to two thirds of the breadth, they may be built with the joints of the upper course of each foot ing resting nearly on the middle of the stones in the course below it.
When the superstructure of a wall consists of unhewn stone laid in mortar, it is called a Rubble Wall, which may be either coursed or uncoursed; of these the latter is very common in ordinary buildings. The greater part of the stones are used as they come from the quarry ; some have a slight hammer dressing. This sort of wall is very inconvenient for receiving bond timbers ; but if bond timbers be preferred to plugging, the backing- must be levelled in every height where the bond timbers are required. When the stones are very small, and of irre gular shape, it will add to their stability to work in slen der laths or old hoop iron ; and care must be taken to dispose the longest sort of the stones so as to create the greatest possible bond ; and the work must be carried very regularly up round every wall of the building, and with not too much rapidity, in order that it may have time to indurate or set, to a certain degree of firmnass,_ before a great weight comes upon it ; and on no account should thin stones be set on edge, which thoughtless and unprincipled workmen arc but too much inclined to, ei ther from haste, or for the purpose of making a smooth out-side facing.