BRICKS AND BRICKMAKING.

Auckland Star, Volume LV, Issue 116, 17 May 1924, Page 5

BRICKS AND BRICKMAKING.

ADVANCES IN AN ANC-ENT ABU The earliest mention of the manufacture of bricks is to be found in the ___toricai books of the Old Testament, where Noah's three sons, together with their wives and children, departed from the eastward and travelled into the land of Sbinar. "And they said one to another, go to, let us make brick, and burn them thoroughly, and they had brick for stone, and slime had they for mortar.' Whether these bricks were really exposed to the action of fire, as the. passage seems to imply, or merely dried in the sun, is a point by no means settled; but according to the testimony of Herodotus—a Greek historian, who flourished between 485 and 424 8.C., and who was on the spot, the bricks which composed the tower of Babylon, were baked in furnaces. Unburnt bricks were used in ancient Egypt, the making of which was one of the tasks imposed on the Israelites during their servitude in that country, but the oldest edifices remaining there are built principally of stone. At what time burnt bricks were introdu_-d, or in what country, cannot be determined, but it is probable that burnt bricks existed in China contemporaneously with the productions in porcelain which date back to 2600 B.C. In England, bricks do not appear to have been generally used until the middle of the 15th century, and the art of brickmaking was undoubtedly introduced by the Romans. Until comparatively recent times all bricks were hand made, and of these there were two kinds —slop moulded and sand moulded. Tho work was usually carried on in the open fields, and the natural mixture of clay and sand called loam, and marl, which consists of lime and clay w-ith little or no sand, were the materials employed in the manufacture. It is to be noted, however, that other materials than loam and marl are extensively used in present day brick manufacture. Apart from what we may consider as the true clays, there are a number of varieties of brick making earths, which do not lend themselves to the plastic processes and consequently are looked on with some disfavour by the ignorant and thoughtless. Among the brickmaking earths may he included various shales, papa, volcanic mud, etc. These materials can only be treated in a dry, or nearly dry state, but when so treated, not only produce the highest quality of goods, but are more economical in their cost of productionCuriously enough it is a fact that the jgcoolgist and chemist are by no means i of one mind regarding earths and clays, and their application, and frequently the skilled and resourceful manufacturer comes forward with productions which completely confound the theories of both scientists. •■*,,„ .... Early English Practice. Y ** r '- To come back to the early manufacturer in England, the general process was the digging of the clay in the autumn and exposing it during the winter to the action of frost and air, called weathering. The clay was next placed in shallow pits or pens and soaked for several days. The next step was to thoroughly work and temper the clay, which was mostly done by the treading of men or animals. When these operations were carried out in the neighbourhood of large towns and where large quantities of bricks were required. The operation of kneading and tempering was carried out in a horsemill, which was the forerunner of the present day pug-milL The plan adopted for slop moulding, so called because the mould is dipped into water before receiving the clay is: the workman receives the clay already worked to proper consistency and throws a conveniently sized lump of the clay with some force into the mould, presses it down with his hands to uniformly fill the mould, and then strikes off the surplus clay with a straight edge. The mould was a rectangular frame of the exact shape and size of the brick, plus the pre-determined allowance to be made for shrinkage in drying and burniing. In operation the sand moulding is ■ identical witj. the slop process, except in that the clay used is of slightly stiffer consistency, and instead of the mould being dipped into the water, the inside is lightly dusted with sand in order to facilitate the delivery of the made brick from the mould. In the latter process a considerable saving of time is effected before the. bricks are dry enough to be taken to the kiln and also t. c bricks are somewhat less disposed to crack and warp in the event of uneven drying. Also the ratio of production is nearly two to one in favour of sand moulded. The slop moulded, however, had used to find much favour and it is curious to note that in the case of ordinary sizes, 9 x 4J x 3 approximately, bricks made by the two different process from identically. the same clay, the slop moulded is denser, closer in texture, and nearly a pound heavier than the sand moulded. When the brick was made, the next process was drying, and in the case of the sand moulded, they were at once set up on their edges in tiers with sufficient space between for air to circulate and so wait until ready for burning. The slop moulded, however, had to be laid flat on one side, either on a drying floor, heated by flues or laid out on boards —either case being an obvious drawback. After being sufficiently dried they were usually burnt in clamps. Tt may be noted that in the handmade bricks there is 25 per cent of water to be evaporated before it is safe to bum them—the* lost about one-fourth their weight in drying and a further one-third in burning. The Process of Burning. A clamp was usually prepared and built by raising its site above the level of the surrounding ground, and draining it so that it be kept free from water. The surface was made dish shaped so tbat when the green bricks were packed for burning they would have a tendency to fall in towards the centre of the clamp. One or two courses were then laid diagonally with about two inches between them! the spaces between the bricks being filled with coke-breeze or fine coal. Flues were left in the layers and filled with wood faggots. Over the diagonal layers about six inches of breeze was spread and on this the first layer of green bricks was laid on cdjie. on which was another four or six inches of breeze. From then on the bricks were built up in alternate layers of headers and stretchers until the required height was reached. The clamp would be ctl practically any size—often from 40 feet to 50 feet square and frequently contained 50,000 to 60,000 bricks. When all the bricks had been stacked and the sides and ends covered with a daub of wet clay, the clamp was allowed to burn for varying periods, sometimes from three to six weeks. . L, S-fr£_-_^ei_?lg-»^,tot^JTi3^

fasgoi- in the arches of the lowes; oaarses, the fire passing upwards from one layer of breeze to the whole clamp was thoroughly burned, and where combustion appeared to be proceeding too rapidly in places * ™* checked by closing tbe arches or covering tt»t part on the top of the clamp with clay or«an__. This manner of burning entailed a great deal of waste; m th_s interior «_ the clamp, wheTe the beat I» greatest, often large numbers of bricks were fused together into a shapeless and useless mass and many on the exterior were insufficiently; burnt, so being soft and friable. Revolution by Machinery. Such was the old order of that branch of manufacture, but in recent years great strides have taken place, both as regards the introduction of machinery and the development of more satisfactory and economical means of burning. "'The introduction of mechanical brick making appears to date from about 1820, and the objective mostly in view was to produce an article ready or as nearly as possible so, for immediate burning, but in this respect, except in special cases and with peculiarly adaptable material, it cannot be claimed to possess any advantages over the present day plastic system. By far more appreciable improvements have taken place in recent times in the planning and construction of kilns. Prom the old style of clamp various forms of the intermittent type have been evolved, on both up and down draught principles, until the introduction of the continuous kiln by Hoffman, Germany, in 1859, practically revolutionised the art of hrickmaking, or, at least, in so far as its perhaps most important operation tends. The size of the modern brick was not fixed by tl_e manufacturers to suit the convenience of either architects or builders; but by English Parliament to meet the Excise laws which prescribed a tax of 5/10 per 1000 - up to 150 cubic inches in conteift and 10/ per 1000 email bricks above this size. Ordinary _a_Ddsxig bricks, ia order -Eharfc ;ood work may be done with them, should ie uniform in size aud shape. Each ihould be of such size and shape tha. ta length is twice its width, plus the hickness of a mortar joint. They should lave true rectangular faces with sharp orrises, and when they are broken the ractured surface should present a uni:orm appearance. The amount of water l brick will absorb also gflbrds a good :est of its quality. Bricks intended for strong'-Vorfe-shcraM lot absorb more than 15 per cent of iheir own weight of water and the water :hat is absorbed should be taken up reluctantly. The brick should also part with the ibsorbed water with facility at an ardinary temperature; i.e., the water absorbed in the brick should readily some from it and leave the brick dry when exposed to ordinary atmospheric influences. All bricks should be uniforcrdy iburnt. _ot vitrified in one part and under baked in another, and when struck together the result should be a metallic clanging sound and not a dull earthy or wooden one.