Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/102

 86 THE BUILDING NEWS. Fes. 2, 1872. steamship, and many other works to which the term ‘ great”’ was not inapplicable if we limit its meaning to size. Sir Isambard Brunel was so confident of the use to be made of brickwork in cement, strengthened with hoop-iron bond, that he proposed to con- struct arches without centreing, where there was to be more than one, by beginning to turn them by equal additions on each side of a pier, inserting hoop-iron bond longitudinally in the spandrels as the work proceeded. The cement he used was one that set very quickly, so that he was able to add course after course with tolerable quickness, always preserving on each side of the pier an equal number of courses until he reached the crown of the arch; and supposing another half-arch to have been in progress from the opposite pier or abutment to meet it, the arch would haye been keyed in, or, rather, it would have re- quired no key, for although in the form ofan arch, the structure wasreallya beam, depend- ing for its stability on the tensile strength of the hoop-iron in the upper part, and on the compressive strength of the brick at and near the springing. de did not propose to turn the arch of the full width at once, but to first turn a rib of about four feet in width, using a templet in the manner in which it is used in building a curved wall, to preserve the form of the arch, and, when the rib had been turned, to add to its width on each side until the required width had been attained. Brickwork is measured by the cubic yard in structures such as bridges, retaining walls, and other large masses, and in the midland and northern counties by the square yard of walling, the thickness being stated as one brick, brick and a half, two bricks, &c., for each of which builders have their prices per square yard. But in the London district walling is measured by the rod, and builders and contractors have become so accustomed to measurement by the rod that other kinds of work are sometimes measured also by the rod. A cubic yard contains 27 cubicfeet; a square yard 9 square feet, Arodis 53 yards in length, or 163ft.; a square rod, therefore, contains 272} square feet. A rod of brick- work is 2724 square feet of the thickness of a brick and a half, or 154in., and as the Ht. is neglected in practice, the rod contains 272ft. x 1fft. = 306 cubic feet, = 111 cubic yards. In walling of various thicknesses the quantity is reduced to the standard thickness of a brick and a half, and is estimated at ‘‘per rod reduced.” Thus, in measuring three walls, one of which is 9in. thick, another 13fin., and the other 18in. thick, the area of each is taken and multiplied into the number of half bricks in the thickness ; the wall 9in. thick by 2, the wall 14in. thick by 3, and the wall 18in. thick by 4; the sum of these divided by 3 shows the number of rods of brickwork reduced to the standard thickness. If odd feet remain over a number of rods the quantity is stated in rods and feet, or in rods and fractions of a rod, or in rods and decimals. Thus, if a wall be measured as 50ft. long, 9ft. high, and one brick thick ; another 30ft. long, 12ft. high, and a brick and a half thick; and another 30ft. long, 18ft. high, and two bricks thick, the measure- ment would stand thus— 30x 9X2 = 540 30 x 12 * 3 = 1080 30 X 18 x 4 = 2160 3) 3780 1260 square feet a brick and a half thick, and 1260 172 372 I79 212 LIZ 4-63 rods. Another method of reducing dimensions to the standard thickness is first to find the number of cubic feetin the work, and then to multiply them 8 times, and divide the product by 9, those being numbers which are proportionate to 12 and 13} respectively, rods, = 433 rods, 68 = 4rods 172ft. = 4 = or, in other words, one-ninth is deducted from the number of cubic feet to reduce them to the standard thickness; thus, taking the former dimensions— S0ft. SiS 9) an = 202'5 cub, tt 30,, X 12, X 134,, = 405 3 80,;, 18S), = SLO 4 14175, 8 9) 11340 1260 sq. ft. a brick and a half thick, as before. In some counties in England, where stone walling is cheaper than brickwork, and also in Ireland, the custom is to measire by the perch. A perch is then understood to be a length of wall of 7 yards, or 21ft., 1ft. high and 18in. thick, that thickness being the usual one for stone walls. If these dimen- sions are reckoned up they come to 314 cubic feet. When the standard thickness of walls is 18in. it is convenient to take an even num- ber of yards or feet, say 7 or 21, for each foot in height, and to call that a perch—in some places a rod, for in olden times a rod, pole, or perch were synonymous terms for the same quantity. But in measuring brickwork by the same standard the difficulty has been that it has been about twice as expensive, so, in measuring brickwork, while adhering to the standard of the perch, or rod of 7 yards, the standard thickness has been proportionately reduced, and for brickwork a perch or rod of walling is taken to be Qin. thick, which gives a cubical measurement of 153 cubic feet. These local customs are very awkward, and insuch aunited kingdomas this of Great Britain and Ireland one would think some more reasonable standard of measurement would be established ; for not only do the different counties in England differ, but, while we adopt the Irish method of measurement by the perch of walling in some counties, we know nothing of it in others. Then in measuring by the rod, as in the London dis- trict, and reducing all thicknesses of walling to one standard of a brick and a half, it is but a rough method, for the proportion of face- work to cubic contents is greater in thin than in thick walls, and ought in some measure to govern the price of the work. Then in re- ducing thicknesses to 1} brick, a brick is as- sumed to be Qin. long and 44in. wide, but bricks of different sorts vary so much in size that a wall may be considerably thicker or thinner than the assumed thickness, and the bricklayer’s work will be influenced by that. Now, a yard is understood all over the country to be 3 feet, or 36 inches; why, therefore, should not a cubic yard be the standard for all common work, and a cubic foot for ornamental work, adding in both cases the superficial measure- ment of the face-work? A builder who has a large business will probably be quite satisfied with things as they are, because at the year’s end he will have done a sufficient amount of work of various kinds to bring to bear the rule of averages, and if he should have lost something in some cases he will probably have gained as much in others; but that is accidental to his large business, and ought not to be reckoned upon in fixing standards of measurement. A yard certainly has the disadvantage of being small, perhaps petty ; then let a name be invented for a measure- ment of 10 eubic yards, which would ap- proach in bulk nearly to a rod. ‘The number of bricks required to build a given cubic capacity of work varies consider- ably with the different kinds of bricks. It is stated in Dobson’s treatise on the manufac- ture of bricks and tiles that bricks are made at Nottingham as large as 9} X 48 x 3 1-16, and that they weigh Slb.; that Suffolk bricks are 9F x 415-16 x 3} in the mould, and that they shrink in drying 7 inch in the length. If we take a proportionate shrinkage in the width and thickness, the dimensions of the brick would be 9 x 43 x 8. The weight is stated to be 6lb. Staffordshire blue bricks are stated to weigh 8lb. loz., and to have a specific gravity of 1-861. It is stated that London stock bricks are 83 x 41 x 23, and that they weigh 5lb. The average thickness of all bricks is pro- bably 2} inches, and when that is the actual average thickness of any particular sort of bricks, four courses to the foot in height makes the best work. In that case it requires about 350 bricks per cubic yard of work ; but taking London stocks at only 24 inches thick, four courses to a foot in height would make the bed joints too thick ; a greater number of bricks, therefore, is required. A rod of brick- work requires 4,500 stocks, allowing for waste; but in house-building, the flues, which are measured solid, and the bond timber, wood bricks, &c., which are measured in, sufficiently allow for waste, and in house- building a rod of brickwork requires 4,300 stocks. The weight of the brickwork varies, of course, with the specific gravity of the bricks, and is influenced by their individual size. If we take the dimensions and weights before stated, we find the specific gravity of Suffolk bricks to be 1:398; of Nottingham bricks, 1:637 ; of London stocks, 1:°654, and of Staffordshire blue bricks, 1-861. On the whole the weight of brickwork in mortar exposed to the weather may be said to average 1 cwt. per cubic foot, or 27 cwt. per cubic yard, or about 15 tons per rod. The quantity of mortar is about one-fifth of the whole mass when the bricks are straight and square, and are well and closely laid, but with the ill-shaped bricks sometimes used one-quarter of the whole mass is mortar. ——— DECORATIVE PROCESSES. GILDING. By an Exrerrencep WorKMAN. (Continued from page 50.) ILDING in oil, as we have before said, is not confined to frame gilding, but has avery wide application. It requires a different preparation of ground to that which has been described as used by the frame gilder, although gilding on the enrichments or ornamental parts of a ceiling or cornice which is finished in distemper willrequire to be in some degree prepared in the same manner to receive the oil gold size. When the ornamental parts of a distemper ceiling have to be part- gilt, those parts will have to be done once with two or three coats of clear-cole or one coat of strong size, in order to prevent the oilfrom sinking into the body of the distem- per, and to prevent its spreading and making ragged edges. When the distemper size is dry, the oil gold size should (in etching) be cut in sharp and clear, and about a sixteenth of an inch inside the margin of the coating of parchment size previously laid on, so as to prevent the danger of its running into the distemper. When the gilding isdone it will require to be backed or brushed over with a coat of weak size and water. Wenow come to gilding upon paint. The grounds for gilding upon in these cases are sometimes dead, i.e., without gloss, and some- times with gloss, and polished, and varnished. But whether the gilding has to be done upon dead or gloss paint, it is essential that the work should be got up as smooth as possible. '’he smoother the surface to be gilt the brighter will be the lustre of the gold when finished. When the work to be gilt is painted with flat or dead colour it it will not require any parchment size as a preparation ; but if the groundwork is a gloss colour, a coating of egg-size will be required, which is prepared as follows :— Make a small hole in each end of an egg, and blow with the mouth at one end, which, if done carefully, will blow out the white of the egg through the other, and into a pint 7