III. RUBBLE-STONE MASONRY. 394. With good mortar, rubble work, when carefully executed, possesses all the strength and durability required in structures of an ordinary character; and it is much less expensive than cut stone. 395. The stone used for this work should be prepared simply by knocking off all the sharp, weak angles of the block; it is then cleansed from dust, &c., and moistened, before placing it on its bed. This bed is prepared by spreading over the top of the lower course an ample quantity of good ordinary-tempered mortar, into which the stone is firmly embedded. The interstices between the larger masses of stone are filled in by thrusting small fragments, or chippings of stone, into the mortar. Finally, the whole course may be carefully grouted before another is commenced, in order to fill up any voids left between the full mortar and stone. 396. To connect the parts well together, and to strengthen the weak points, throughs or binders should be used in all the courses; and the angles should be constructed of cut or hammered stone. In heavy walls of rubble masonry, the precaution, moreover, should be observed, to lay, the stones on their quarry-bed; that is, to give them the same position, in the inass of masonry, that they had in the quarry; as stone is found to offer more resistance to pressure in a direction perpendicular to the quarry-bed than in any other. The directions of the lamina in stratified stones show the position of the quarry-bed. 391. Hammered stone, or dressed rubble, is stone roughly fashioned into regular masses with the hammer. The same precautions must be taken in laying this kind of masonry as in the two preceding. IV. BRICK MASONRY. 398. With good brick and mortar, this masonry offers great strength and durability, arising from the strong adhesion between the mortar and brick. 399. The bond used in brick-work is very various, depending on the character of the structure. The most usual kinds are known as the English and Flemish. The first consists in arranging the courses alternately, entirely as headers or stretchers, the bricks through the course breaking joints. In the second the bricks are laid as headers and stretchers in each course. The first is stated to give a stonger bond than the last; the bricks of which, owing to the difficulty of preventing continuous joints, either in the same or different courses, are liable to separate, causing the face or the back to bulge outward. The Flemish bond presents the finer architectural appearance, and is therefore preferred for the fronts. of edifices. 400. Timber and iron have both been used to strengthen the bond of brick masonry. Among the most remarkable examples of their uses are the well, faced in brick, forming an entrance to the Thames Tunnel, the celebrated work of Mr. Brunel, and his experimental arch of brick, a description of which is given in the Civil Engineer and Architect's Journal, No. 6, vol. I. In both these structures Mr. Brunel used pantile laths and hoop iron, in the interior of the horizontal courses, to connect two contiguous courses throughout their length. The efficacy of this method has been further fully tested by Mr. Brunel, in experiments made on the resistance to a transversal strain of a brick beam bonded with hoop iron, accounts of which, and of experiments of a like kind, are given by Colonel Pasley in his work on Limes, Calcareous Cements, &c. 401. The mortar-bed of brick may be either of ordinary or thin-tempered mortar; the last, however, is the best, as it makes closer joints, and, containing more water, does not dry so rapidly as the other. As brick has great avidity for water, it would always be well not only to moisten it before laying it, but to allow it to soak in water several hours before it is used. By taking this precaution, the mortar between the joints will set more firmly than when it imparts its water to the dry brick, which it frequently does so rapidly as to render the mortar pulverulent when it has dried. 402. On this point the late General Totten, Chief of Engineers, in his instructions for building brick masonry, observes: "The want of cohesion" between the brick and mortar, in the case of some gun practice against brick embrasures," was due to the interposition of dust, sometimes quite free, but more generally composing a layer slightly cohering to the body of the bricks. The process of laying must be to cause every brick to be thoroughly soaked in water, and to be laid the moment it ceases to drip." 403. Concrete Walls. The use of hydraulic concrete for the construction of both solid and hollow walls for houses has very much increased within a few years; and it is claimed that they are drier, stronger, and cheaper than walls of brick of equal thickness. In some of the cheaper structures of this class put up in Paris, the concrete was composed of one part in volume of Portland cement, and from five to eight parts of clean screened gravel from the size of pearl barley to that of peas; and in some cases instead of gravel what is known as brick ballast, or the small fragments of ordinary brick from which all the fine dust is screened out, is used, taking eight parts of this to one of Portland cement. 404. For building walls of concrete where a scaffold is not necessary it is only requisite to have a boxing formed of scantling and boards of the width of the wall within, between the two sides of which the concrete is thrown in and rammed. 405. For solid walls requiring a scaffolding, what is termed Tall's bracket scaffolding is used. The concrete is laid with B Α Fig. 28 represents a vertical section of the boxing for laying concrete walls. A, Boarding confined by clamp screws. B, Platform supported by brackets and clamp screws. in the boxing, which consist of boards, A, held together by clamp screws, b, which pass through hollow iron cones placed between the sides of the boxing, which, within, is of the same height and width as the layer of concrete to be laid at a time. When the layer is finished the boxing is taken apart, and the holes left by the cones when removed are used for securing the brackets of the scaffolding, which consists of triangular frames, B, each formed of a vertical pin, a horizontal beam to support the flooring, and an inclined strut to support the outer end of the horizontal beam. The flooring, of sufficient width for the workmen, projects beyond the wall on each side, and the two parts without and within are held together by clamp screws which pass through the holes. When cylindrical flues are to be left within the body of the wall, a cylinder C, with a handle to it, of the requisite diameter, and the length of the thickness of the layer, is placed in position, and the concrete rammed well around it. When a new layer is to be laid the cylinder is drawn up from the one finished. 406. For constructing either solid or hollow walls, an apparatus devised by Mr. Clarke of New Haven, Conn., termed Clarke's adjustable frame for concrete building, is used. This consists of a boxing of boards, A, for laying the concrete which is held together by frames, each composed of a horizontal piece, B, to which are affixed two vertical clamping pieces, C, the interior piece being movable and capable of being adjusted by screws, the two pieces being held together by a clamp screw, a; the frames and boxing being attached to vertical supports, D, within the building, in which holes are arranged at suitable distances to admit of the frame being placed at the proper height. For hollow walls a wedgeshaped board, b, two inches and a half thick at its broad end, and two inches on the other, is used. This board has rectangular notches of the width of a brick, and placed at twenty inches apart, cut into the narrow edge. This forms the core for the hollow portion of the wall. The work is started or continued by placing the bricks in place lengthwise across the hollow so as to tie the exterior and interior portions of the wall together. The core is then placed with its notches fitting on the bricks, and secured in a vertical position, the concrete is filled in on each side between the sides of the boxing. When the layer is finished the core is drawn up. For further applications of Coignet Béton, see Prof. Barnard's Report on the Paris Exposition of 1867, and Gen. Gilmore's Paper, No. 19, on Béton Aggloméré. 407. Uses of beton agglomere in Europe and elsewhere. The most important and costly work that has yet been undertaken in this material is a section, thirty-seven miles in length, of the Vanne aqueduct, for supplying water to the city of Paris. This aqueduct, which traverses the forest of Fontainebleau through its entire length, comprises two and a half to three miles of arches, some of them as much as fifty feet in height, and eleven miles of tunnels, nearly all constructed of the material excavated, the impalpable sand of marine formation known under the generic name of Fontainebleau sand. It includes, also, eight or ten bridges of large span (seventy-five to one hundred and twenty-five feet) for the bridging of rivers, canals, and highways. The smaller arches are full centre, and are generally of a uniform span of 39,37 feet, with a thickness at the crown of 15 inches. Their construction was carried on without interruption through the winter of 1868-'69 and the following summer, and the character of the work was not affected by either extreme of temperature. The spandrels are carried up in open work to the level of the crown, and upon the arcade thus prepared the aqueduct pipe is moulded in the same material, the whole becoming firmly knit together into a perfect monolith. The pipe is circular, 6 feet in interior diameter, with a thickness of 9 inches at the top, and 12 inches at the sides, at the water surface. The construction of the arches is carried on about two weeks in advance of work on the pipe, and the centres are struck about a week later. Water was let into a portion of this pipe in the spring of 1869, and M. Belgrand, inspector-general of bridges and highways, and director of drainage and sewers of the city of Paris, certified that "the impermeability appeared complete." 408. Another interesting application of this material has been made in the construction, completed or very nearly so, of the light-house at Port Said, Egypt. It will be one hundred and eighty feet high, without joints, and resting upon a monolithic block of béton, containing nearly four hundred cubic yards. 409. An entire Gothic church, with its foundations, walls, and steeple in a single piece, has been built of this material at Vesinet, near Paris. The steeple is one hundred and |