1900c. The mortar or cement should be such as will quickly set, to prevent the superincumbent weight pressing the joints closer, and thereby causing settlements, which even with the greatest care, often take place unequally. As o'ten as it is conjectured, from the nature of the soil, or from the foundation being partly new and partly old, that the work will not come to its bearing equally, it is better to carry up the suspected parts separately, and to leave at their ends what are called toothings, by which junctions may be made when the weaker parts have come to their regular sound bearing.

1900d. The thickness of walls has furnished the subject of previous pages: we shall therefore only add, that too much care cannot be bestowed on strengthening all angles as much as possible, and well connecting the return of one wall into another; that piers or pilasters are exceedingly useful in strengthening walls, inasmuch as they act by increasing the base whereon the whole stands; and, lastly, that in carrying up walls to any considerable height, it is usual to diminish their thickness by sets off as they rise. IR houses, above the ground-floor, the sets off are usually made on the inside, having the outside in one face; but, if it be possible, it is better to set off equally from both faces, because of the better balance afforded.

1900e. Joints in brickwork are finished on the face in several ways. The most common are the struck joint,' which is merely finishing the joint by drawing the point of the trowel along it or jointed,' as done by a tool called a jointer (par. 1890, art. 8), so as to leave a line impressed on the mortar : or 'flush joint, in which case the joint is drawn at top and bottom with the trowel when the brick is laid, and afterwards when the mortar is partially set, the middle of the joint is flushed flat with the jointer;' this is sometimes called a 'high joint.'

1901. A bricklayer, with the assistance of one labourer. can, if he be so inclined, lay in one day about 1000 bricks in common walling; but the trades unions now prevent him from laying more than about one-third that number. Occasionally, for a higher remuneration some non-union man may be found to lay near the former number, and then he would complete a rod of brickwork in four days and a half, its area being 2724 feet superficial of the thickness of one brick and a half. When, however, there are many apertures or other interruptions to his work, he will be proportionably longer over it. The weight of a rod of brickwork is about 13 tons. Generally may be taken as consisting of from 4300 to 4500 stock bricks, allowing for waste according to the quality of the bricks. 27 bushels of chalk lime, and 3 single loads of drift sand, or 18 bushels of stone lime and S single loads of sand. In cement, of 36 bushels, and the same quantity of sharp sand. A rod of brickwork laid dry contains 5370 bricks. A cubic yard contains 384 bricks, and requires about 64 cubic feet of sand and 2 of lime. A ton of bricks contains about 373 on an average. 330 well burnt bricks weigh generally about 20 cwt., so that a cubic foot weighs about 125 lbs.

1902. Brick-nogging is a method of constructing a wall or partition with a row of posts or quarters 3 feet apart, whose intervals are filled up with occasional plates of wood with brickwork between. It is rarely more than the width of a brick in thickness, and the bricks and timbers on the faces are flush. It should never be used where thickness can be obtained for a nine-inch wall. A half brick nogged partition will require about 500 bricks; a whole brick-nogged partition about 1000 bricks; and with brick on edge about 340.

1902a. A half-brick partition built in mortar is now adopted in many of the model lodging houses, sometimes with an occasional hoop-iron bond. These are built four, five, and six stories in height, the joists of the floors steadying them as they are carried up. Of course the apartments in such places are small in all their dimensions, being about 12 feet long, 9 feet wide, and from 9 to 9 feet 6 inches in height. A half-brick wall of greater dimensions may be built in cement, and when the floor joists are laid upon it, it becomes very steady, strong, and little likely to be injured by a fire. Thin slabs of stone have been used as partitions in small houses near a quarry. Tiles in cement with wood plugs inserted for the dressings, make a sound partition, and when plastered direct upon the tiles, it takes up much less room than a one-brick wall.

C

B

19026. Many varieties of hollow bricks are made for a similar purpose. The "patent bonded hollow bricks or rebated tiles "(fig. 617a.) of Hertslet and Co., were employed in 1846-7, by Henry Roberts in the model lodging house in George Street, St. Giles's; as also in the so-called Prince Albert's model houses, erected in Hyde Park in 1851, and removed to Kennington Park. A is a bond stone; B concrete, C floor boards, and D a tie rod. When used for partitions, or for roof and floor arches, these hollow bricks are fireproof, deaden sound more effectually, and are considerably ligher, than solid brickwork. bricks as a lining to stone or flint walls, supersede the necessity for battening. They are also well adapted for cottage Boors. Hollow bricks can be made by any good tile machine,

Such

Fig. 617.

in the same manner as ordinary drain-pipes. They are more compressed, require less drying, and are generally better burned than ordinary bricks. An interesting and complete paper on the subject, with illustrations on the English and French systems of making hollow bricks, is given in the Building News for 1858.

1902c. HOLLOW WALLS, formed of ordinary stock bricks, were employed for two-story cottages early in this century. Three methods are usually adopted in the construction of a wall. I. All the bricks placed on edge, as fig. 6176, the stretchers and headers breaking joints, and the headers

forming the

bond.

Many persons consider that this arrangement produces a disagreeable appearance on the outside face. II. All

the bricks laid flatways, but the stretchers are sawn in half, so as to leave a space of 4ins. between them; and in laying the headers, as fig. 617c. care must be taken only to fill up with mortar the joints

Fig. 617c.

Fig. 6176.

III. To

over the half brick on edge, so as to leave the middle of the joint open. lay all the bricks flat in the usual English bond, leaving a space of about 2 inches between each face, and to make up the thickness thus caused. viz. 11 or 11 inches, by a bat to each header. This may be varied by using a less number of headers, and placing two or three stretchers together, according to the strength of the work required. At Southampton, and perhaps elsewhere, headers are not used, the two faces being bonded together by hoop-iron cramps (fig. 617d.), with forked ends, ths byth inch, tailing into the frogs of the brick

(fig. 617e.), and having a bend in the middle of its

length partly as a strut to the inside, and partly to prevent any moisture

running along it to the inside face. A cast iron cramp (fig. 617f.) is also made, inch by ths in. thick. Jennings has adopted bonding bricks of stoneware for hollow walls. Fig. 617g. shows the application of the three sizes; A is 13 inches long, to be used in garden walls and other places where an uniform face is not required; B is 11 inches long,

A

B

c

Fig. 617g.

Fig. 6174.

where but one uniform face is required (the brick is shown to a larger size in fig. 617h.) the end of the bond brick being faced with a closure of the same material as the wall; and C is a brick 9 inches long, when both faces are to be uniform, closures being used at both ends of it. A 16 inch hollow wall can be built with a 9 inch inside wall, a 2 inch space, and a 4 inch wall outside, and so on. Such a wall is of very common erection in North America, and it is found to stand very well for country villas of good dimensions.

1902d. Much diversity of opinion exists as to whether the space so left should be ventilated by air gratings just above the ground, and also by others under the coping, to obtain a current of air and secure dryness if water be blown through the outer brick work. In exposed situations, especially on the sea-coast, if hollow walls are not built, either the wall has to be slated on the outside; or it has to be battened on the inside, even when cemented on the outside, to prevent damp showing on the interior surface. Hollow cement blocks have lately been introduced in France, and are said to be cheap, as durable as stone, ventilation easily secured, and provide for the ready formation of shafts for warm air or for flues. The blocks have a resistance of 430 lbs. to the square inch, and are adapted to walls about 20 inches thick as well as to partitions of less width.

1902e. Mr. Taylor has adopted an arrangement of an interior face of common bricks B, with an exterior facing block of a better manufactured brick A, in the shape of the letter

I, leaving a cavity of 2 or more inches between them, (fig. 617i).

1903. GROINED ARCHES. A groin is the angular curve formed by the intersection of two semi cylinders or arches. The centering for raising the more simple groins that occur in using brick arches, belongs to the section CARPENTRY. The turning a simple arch on a centre only requires care to keep the courses as close as possible, and to use very little mortar on the inner part of the joints. executing a brick groin, the difficulty arises from the peculiar mode of making proper bond, at the intersection of the two circles as they gradually rise to the crown, where they form an exact point. At the intersection of these angles, the inner rib should

In

Fig. 6171.

B

be perfectly straight and perpendicular to a diagonal line drawn on the plan. After the centres are set, the application of the brick to the angle will immediately show in what direction it is to be cut. With respect to the sides, they are turned as for common cylindrie vaults. Mr. George Tappen, an ar

chitect of great practical skill, introduced a method of constructing groins rising from octangular piers, which had the advantage of not only imparting strength to the angle, which in the common groin is extremely deficient, but of increasing the space for the stowage or removal of goods, and further, of strengthening the angles of the groin in this construction by carrying the band round the diagonals (fig. 617k.) of equal breadth, and thus affording better bond to the bricks.

1903a. The Metropolitan Building Act, 1855, requires that under a public way, an arch, if it be employed, of a span of not more than 10 feet, is to be at least 8 inches thick; when not exceeding 15 feet, it must be 13 inches at least; and beyond that width the thickness requires special appro

Fig. 617k.

bation. If of iron construction or other incombustible material, it must be built in a man ner approved by the district surveyor. An arch over a public way must be formed in the above manner, but a span not exceeding 9 feet must be 84 inches thick at least. A like special approval is required if the arch or floor be of iron.

FIREPROOF ARCHES, FLOORS, AND ROOFS.

1903b. Light arched flat floors, composed of bricks cemented with gypsum or plaster, have been in common use in Roussillon from time immemorial. Rondelet is of opinion that the segment of a circle is a better form for such arches than the low semi-ellipse. He describes apartments of 18 feet by 25 feet, as used at the War Office at Versailles, covered with brick arches of which the rise was onlyth part of the span and in five stories. The coach-houses and stables of the Marshal de Belle Isle at Bisy near Vernon, were arched in an elliptical form, having a rise of th of their span, which was 32 feet 9 inches. They were not finished until a year after the walls and roof had been completed. The walls were built of rubble-work having chains of cut stone at intervals of about 16 feet. They were 2 feet 8 inches thick, being about equal to th part of the span. These arches were formed of a double thickness of bricks laid flat, and in plaster, built in succession, with the vertical joints broken. The haunches were filled up with rubble stone in plaster. The springing was formed by notches in the wall, above which the regular courses of stone projected inwards as gathering courses. Above all, a third course of flat bricks was laid horizontally, forming a pavement. Rondelet considers that arches of small and light materials cemented by gypsum become as it were one body, and exert little or no lateral pressure upon the abutments excepting at first, because that cement has a tendency to swell in setting. Rondelet relates that a stone of 4000 lbs. or 5000 lbs. weight was dropped upon one of these arches from a height of 4 or 5 feet, which made a large hole through the arch, without doing any further injury. If mortar be used the parts must be thicker, and the centering left, until the work has set. Portland and Roman cement might be better than gypsum for work in England. Rondelet also states that it is better to use coved arches springing from the four walls, than a common arch springing from two opposite walls only.

1903e The arch brick floors, used in the dwell ngs for workmen at Birkenhead, by the architect, C. E. Lang, were 7 feet in span, worked in half-brick except at the springing and the skew-backs, with a few three-quarter and other parts of bricks inserted, so as to form a toothing or vertical bond with the concrete with which the spandrels were filed. The six or seven courses at the crown were wedged in with slate while the mortar was wet, and in no instance did the least subsidence take place at the crown, although subjected to very severe trials, such as that of men jumping from the walls upon the arches. The span of 7 feet is perhaps the limit of a half-brick arch turned in mortar with the ordinary rough brick. The arches rise about one inch to every foot in span. Tiles were laid in mortar on the concrete, which made the thickness of the floor at the crown of the arch 53 inches. There were altogether about 1200 arches of this kind turned, and without the slightest accident. This explains the usual method of forming fireproof floors, by turning brick arches between iron girders, which are in large spans tied together at the springing by iron tie rods; a subject which has been so often considered and discussed, and nowhere more so than at the Institute of Architects, as detailed in their Transactions.

1903d. The Denn tt arch. A fireproof system, patented by Messrs. Dennett, of Not tingham, and used since about 1855. They execute a groin, dome, or circular ceiling of any length, width, or height, wi hout tie rods or intermediate supports, at much less c st than can be done by any other fireproof material: circular ceilings of 36 feet diameter, with coffers in them, or any amount of decoration, can be executed on the soffits, and the upper surface can be finished sinooth in itself, or with stone, wood, tiles cement, or asphalte, and a current of air ensured underneath. Very few iron girders are required. For floors, although in an arched shape, it is in reality a beam, as a complete floor can be turned from wall to wall, resting on a projection of brickwork, and the material be left without any abutment Its durability equals stone; and its strength is equal to brickwork. The floors are bad conductors of heat; leave no harbour for vermin; ventilating pipes may be laid in them, and also flues. The material (a concrete of broken stone or brick embedded in gypsum calcined at a red heat) can be be used for a sound-proof construction, when laid in the old method between wood joists, as at St. Thomas's Hospital.

1903e. Three courses of plai tiles laid in cement and well bonded have been for many years employed for slightly curved roofs to form terraces; roofs for cellars under paving; as roofs over small back buildings, and for similar purposes. Where the walls are well backed

up, tie rods may not be necessary. It has been asserted that the tiles should not be covered with the cement. Portland or other cements laid on brick arches, or on tile, or on a flat concrete roof supported by iron joists; also asphalted roofs; all generally crack and let in wet, especially where there is any traffic on them, or their foundations are not perfectly stable. At Austin and Seeley's artificial stone works, New Road, flat roofs, floors and steps are formed in their material. The terrace roofing is formed of plain tiles in three courses, rendered on the top to the thickness in all of about 4 inches, carried over by arches slightly cambered, springing from small brick piers, and tied by light iron rods, which form their chord line. These flats have an immense weight upon them, and are cast in one piece, as it were, there being no perceptible joint; they are completely water-tight, and can be easily cleaned.

1903f. Light arches may likewise be formed by placing thin iron plates between joisting of iron or wood, bending them to a slight curve, and filling in above them with concrete to form solid work. Mallet's buckled wrought iron plates, are usually made in square or oblong shapes, having a slight convexity in the middle, and a flat rim round the edge, called the fillet. These plates are considered the best form yet devised for the iron covering of a platform, and are usable for the above purposes. They are often placed so that the convex part is compressed, and the flat fillet stretched; when they give way under an excessive load, it is usually by the crushing or crippling of the convex part. The safe loads given in the tables published by the inventor, for a plate 3 feet square, inch thick, and with 1.75 inch of curvature, are 4.5 tons for a steady load, and 3 tons for a moving load. The square form, supported and fastened at all the four edges, is the most favourable to strength. The buckled plates used by Mr. Page for the platform of new Westminster bridge measure 84 inches by 36 inches, with a curvature of 3inches, and thickness of inch; they bear 17 tons on the centre without giving way (Rankine, Ciril Engineering).

1903g. In India, where all buildings of any importance have flat roofs, the long established practice is to form them of tiles, mostly 12 inches square and 1 inches thick; in Calcutta they are generally 18 inches square and 2 inches thick. These tiles are made with great care: they are burnt the same as pottery, and are used both for roofing and for flooring. In roofing a room of 20 feet span, it is first covered with teak beams 12 inches deep by inches broad, placed 3 feet apart, which carry burgahs or joists, 3 inches square, fixed 1 foot apart, and on these the tiles are placed in two layers carefully jointed with each other. Above them is laid 6 inches of concrete, formed of broken bricks and lime, spread evenly and beaten down to 4 inches, and beaten until the mass is dry; finally it is plastered, and rubbed or polished. If well made and of good materials, it is impervious to wet, and will last as long as the timber under it.

1903h. A floor, or even a flat roof, patented by Bunnett in 1858, is formed of hollow ricks, having the two sides each composed of two parellel inclines, and each about half the depth of the block, connected by a horizontal or nearly horizontal plane, and the two inclines on one side are parallel with those on the opposite side. Through these bricks tie rods are passed, and secured at each end to wall plates formed of angle iron; the whole is then screwed up, when the bricks form a slight curved arch in section, and from the inclined sides they over and underlap one another and mutually give and receive support from the neighbouring blocks. This invention has been carried to 21 feet span with a rise of about 2 inches, and about 13 feet wide. Other arches have been constructed for the purpose of testing its bearing powers. One of the latter, 15 feet beween the bearing walls, and 2 feet 3 inches wide, was loaded with 4 tons 10 lbs. (or 267 lbs. to the square foot), and was quite elastic. The detection was about ths of an inch. The bricks are put together with Portland cement and sand. Each brick is 103 inches long, by 93 inches wide, and 6 inches thick, and weighs 21 lbs. 100 square feet comprise :-

1903i. Pots and jars and hollow bricks have all been used in arched work to reduce its weight. Sr John Soane employed jars in the dome of the Rotunda at the Bank of England, which is about 65 feet in diameter. In floors of arched work either iron ties must be used to prevent the walls being forced out, or iron girders employed, thus subdividing the length, and the work arched across the length, i.e. between each girder. The Builder of 1849 records the use of hollow bricks in the vaulting of St. George's Hall, at Liverpool; and Daly's Revue Générale for the same year, the use of such bricks in walls. 1903k. The Indians about Nagpore build their stone vaults in a peculiar method, which might be followed with advantage in some cases in this country. At the springing, stones of a considerable depth are used, having the intrados cut to the form of the curve; six courses are laid, the upper one having a groove 5 inches wide and 2 deep. Then stones of a smaller depth are laid, each having a groove cut in one face, 2 inches in depth and 4 inches in breadth, with a corresponding projection in their other face, the groove being on the upper side to receive the projection formed in the next course. About eight courses having been laid, it then becomes necessary to prevent the work from falling inwards. At every 10 feet in length two strong rods are placed horizontally across the chasm, and the ends are forced into the grooves. From these courses as from a new base similar grooved stones to those already described are continued, the length of each course contracting until the key course is inserted. When this last course is complet. d, the rods are swn across at either end of the finished vault, and the work continued. When the arch or vault is of considerable span, a series of bases may be adopted, each at higher pints than the other, until one part is keyed. A slight scaffolding supports the workman, but no frame or centreing is used.

19037. In view of a fire, and for the preservation of property and life, fireproof floors should be more constantly insisted upon to replace the common wood floors, which (as has been described) usually "consist of one inch of boards and one inch of plastering to separ ate each story in a dwelling." Even these can be improved by some modern inventions. An American (Wight) method is by fixing flat interlocking fireclay tiles, carried by iron clips screwed to the underside of the joists, the underside of these tiles being grooved to formed a key for the plaster. A space of 2 inches is thus left between the plaster and the wooden joists, and as the tiles themselves will stand almost any heat that can be brought to bear on them, the joists are absolutely protected; on the upper side fine concrete or pugging might be used. This system can be affixed to existing floors by simply hacking off the lath and plaster, and it is probably quite new in this country. (J. Slater, New Inventions, in Royal Inst. of British Architects, Transactions, 1887.)

1903m. In the so-called "flats" and suites of offices, the floors are now generally formed of fireproof construction. There are many modern systems. The core or material used to fill in between the wrought-iron joists, which are placed 2 feet to 3 feet apart, is generally determined by local circumstances, or the patent of the inventor of the system. These are, metallic concrete, coke breeze, pit or river ballast, broken stone, broken brick, well-burnt clay ballast, granite chippings, pumice, pots, &c., all generally set in cement. This preparation is covered by an asphaltic, granitic, or metallic surface. Lastly, the upper surface is finished with a floor of boards nailed to small wood joists or sleepers resting on the concrete; blocks are also used for fixing them.

1903n. Archibald D. Dawnay's fireproof flooring is stated to be the simplest, cheapest, and strongest ever introduced; suitable for all buildings to 40 feet span without columns, being composed only of steel or iron joists embedded in a high class con