CHAPTER XIII Tue MATERIALS Usep IN SANITARY WoRK (Part 2)

turned over together two or three times before the water is added. The proportions range from one part of cement to one of sand, to one of cement and four sand. For jointing drain pipes, joints of brick sewers and similar work, one of cement and two of sand is a good proportion. Not more should be mixed than is immediately THE MATERIALS USED IN SANITARY WORK 423 required, as mortar which has commenced setting should not be re-mixed. Concrete. As will have been seen, concrete, which is really an artificial stone, is largely used in sanitary work. There are two chief varieties of concrete, lime concrete and cement concrete; but the former is now but little used, cement concrete being desirable for any work required to be waterproof. Bituminous concrete is also sometimes used, this being a compound of bitumen with broken stone, the former taking the place of cement. Cement concrete consists of three materials, Portland cement, sand and a larger aggregate, such as broken stone. The cement and sand, which has been sufficiently described above, together form a matrix or mortar which binds together the aggregate. The aggregate may be of broken stone, broken bricks, gravel, Thames ballast, coke breeze or furnace slag; the remarks made about the two last-mentioned materials, when dealing with sand, will, however, apply with equal force to their use as aggregates and they are not generally used in sanitary works. If unscreened gravel or Thames ballast is used no sand will be needed in addition to that which is contained in the ballast. This material is of un- certain quality. It used to contain about a reasonable amount of sand for the making of concrete, but now very often contains far too much. It all depends on the part of the river from which it is obtained and must therefore be regarded with caution. Substitutes for Broken Stone. Whatever the nature of the aggregate chosen, it should be free from clay, loam and earth, or else freed from these by washing. If stone or brick is used, it should be broken to a size suitable to the character of the work to be executed, only pieces which are capable of passing through a screen of specified mesh being used, whilst small stuff, which passes through a much smaller screen, should be rejected. Gauge of Aggregate. For heavy retaining walls or foundations the material should be capable of passing through a screen of 2 inches or 24 inches mesh; for work which is to be watertight, such as the walls of a sedimentation tank, a gauge of 1 inch would be reasonable, whilst for thin slabs of concrete and for reinforced concrete the maximum gauge should be about ? inch. Proportions. The proportioning of the materials is of great importance, the ideal proportion for strength and watertightness being that in which the cement completely fills the voids between the grains of the sand, and the matrix so formed completely fills the voids between the pieces of the larger aggregate. This pro- portion can be determined roughly in the following manner. A 424 THE MATERIALS USED IN SANITARY WORK watertight box of known capacity is filled with the broken stone and water is poured in until the spaces between the stone are completely filled; the volume of water is carefully measured as it is poured in and this will be an indication of the amount of sand required. A similar test can be conducted on the sand, the amount of water added in this case being an indication of the amount of cement required. It will generally be found that the proportions arrived at by these means will be about one part of cement, two parts of sand and four parts of stone, so that in reinforced concrete and other work which has to be watertight, these proportions can be used if great care is taken in the mixing. To allow for uneven mixing the proportions may be 1, 1? and 34 in important work. For the foundations of ordinary buildings, for support of sewers and other work in which watertightness is of no importance and only moder- ate strength is required, the proportions are commonly made 1, 3 and 6 respectively. Watertight Work. Where a strong or watertight concrete is required the proportion of water added is of great importance and should be carefully controlled. It should be as little as is possible in order to produce a concrete which is easily workable. This proportion will vary with different aggregates and sands according to their initial wetness and their porosity. Only clean water should be used. Concrete Mixing Machines. Concrete is preferably mixed in machines, in which there are fittings for measuring the various materials, including the water. In cases where a mixing machine cannot be used the ingredients should be carefully measured in gauging boxes and tipped on a boarded platform. They should then be turned over carefully at least twice, to mix them thor- oughly, in the dry state. After this, clean water should be added through a rose, and the whole turned over again at least twice in its wetted condition. Concrete should not be tipped from a height, or the heavier particles will separate from the lighter. It should be gently lowered into position, deposited in layers not more than 1 foot thick, and each layer well rammed. If any layer has set before the next is added, it should be allowed to set hard and should then be roughened, brushed, wetted and coated with cement and water, a mixture known as “cement grout’’, before a fresh layer is put on. Manufacture of Ware Pipes. The relative advantages of stone- ware and fireclay for the manufacture of drain pipes have already been referred to. They are both manufactured, by machine, in THE MATERIALS USED IN SANITARY WORK 425 the same way. The machine is arranged so as to extend through two floors of the building. On the upper floor is a steam cylinder, working a steel ram up and down. Below the ram is a hopper or funnel, formed in the floor and into which the clay is charged. Connected to the outlet of the hopper, and situate in the room below, is the steel pipe mould, having a core inside it, the socket being lowermost. There is a space between the core and the mould, which, if filled, and the mould and core then removed, would leave the partly finished pipe. At the lower end of the mould is a small platform which can be readily raised or lowered, and on this is the socket part of the core. The clay is charged into the hopper and the ram allowed rapidly to rise and fall, so as to make the mould compactly filled; clips, holding the platform to the base of the mould, are then released, and the ram allowed slowly to come downwards. This causes the pipe to descend out of the mould, following the movable platform downwards. When a sufficient length of pipe is through the mould, it is cut off by a thin steel wire to a length rather greater than its ultimate length. It is then taken to a revolving table, cut to its true length, trimmed up, and the grooves on the socket and spigot formed. The platform is brought up to its original position, re-clamped, arid the operation goes on again and again. Bends are formed by the pipe moulder taking the lower end of the pipe, as it issues from the mould, and pulling it round to the desired eurve. Junctions are formed of two pipes moulded as just de- scribed, a hole being cut in the side of the one, and the other cut to fit, the moulding being carefully completed by hand. More complicated pieces of stoneware are moulded in two halves and then put together, the joint being carefully made good. Drying and Burning. ‘The next step is to dry the articles, which is generally done in a drying shed, often over a kiln. They are then stacked in a dome-shaped kiln, having fire holes around its base, and burned for about three to four days, according to the composition of the clay. While in the kiln they are, when suffici- ently burned, glazed by the vaporisation of common salt, applied either at the fire holes, or at the top of the kiln. The heat decom- poses the salt into a gaseous vapour which coats every atom of exposed surface in the kiln, and forms an alloy with the surface of the clay. For this reason the salt glaze cannot be chipped off the pipe without taking off also a piece of the pipe itself. An alternative method of glazing, of greater expense, and with many disadvantages, is that known as lead glazing. This is applied, after the pipes or other articles have been burned and removed 14* 426 THE MATERIALS USED IN SANITARY WORK from the kiln, by coating them with a mixture containing, among other things, oxides of lead and tin, silica, china clay, and borax. This forms, when burned in another kiln at a temperature of about 1000° F., a thin surface coating of a glassy nature, but one which does not combine with the material of the pipe, and can be readily chipped off. Stoneware pipes, if required to be of “tested” quality, are tested by means of a hydraulic press, the objects of the test being to ascertain their powers of resistance to absorption, percolation and pressure. As mentioned in Chapter [IX the British Standards Institution have issued standard specifications for salt-glazed pipes and for tested salt-glazed pipes; to these standard specifications reference can be made in any specification for work (B.S. No. 65 for pipes and B.S. 589 for the corresponding fittings). Cast Iron, Wrought Iron and Steel. The manufacture of these materials is too large a matter to be dealt with fully in a work of this kind, but the difference in composition and properties can be dealt with. The main difference in composition is in the propor- tion of carbon contained. Cast iron contains from about 2 to 6 per cent., wrought iron from 0 to 0-15 per cent., and steel from 0-12 to 1°5 per cent. Cast iron is obtained by smelting the ore in blast furnaces and running the metal into moulds termed pigs. The pig iron should be remelted in order to obtain a good quality of iron. There are three kinds of cast iron, white, grey and mottled, which contains both the grey and white varieties. White and mottled cast iron are less liable to rusting than the grey variety, but the last men- tioned is the material which, for its greater toughness, is used for structural castings. Cast iron is crystalline in structure, gives but little resistance to tension, but great to compression. It is lacking in toughness and elasticity, being hard and brittle. Wrought iron is obtained from cast by a series of processes, the object of which is to remove the carbon and the impurities which made the cast iron brittle. Wrought iron is of fibrous structure, very tough and ductile, easily forged and welded but not fusible, and gives high resistance to tension, though but little to compression. Steel may be produced by adding carbon to wrought iron, or by removing a portion of the carbon from pigiron. There area large number of processes by which this may be brought about. Mild steel is a material which is superior to wrought iron for all ordinary structural uses, principally in that it is stronger and more uniform THE MATERIALS USED IN SANITARY WORK 427 in texture. It has great tensile strength, and has greater resistance to compression than wrought iron, with a harder surface. It is also more elastic in nature. Mild steel is forgeable and weldable, like wrought iron. Given pieces of the same bulk. cast iron of good quality will last much longer than wrought, because of the rapid way in which commercial wrought iron goes to pieces by flaking, a process which does not apply to cast iron. Iron Pipes. Cast-iron pipes are formed in a mould usually having a core in the middle. They can be cast horizontally, vertically or in an inclined position. All three methods are in use, but the vertical method is best, though perhaps less conveni- ent toadopt. It gives pipes of more uniform thickness and greater density. The inclined method, in which the mould is placed at an angle of about 45° with the horizontal, also gives a good quality of pipe. The horizontal method is used chiefly for the lighter kinds of pipe, and does not give such a good pipe as either of the other methods. With the vertical method the pipe is cast with the socket downwards, to give maximum density at that part, and is cast of greater length than needed, by from 6 inches to a foot, so as to allow the dross and air bubbles to rise to the top, this part being afterwards cut off. “Spun” Iron Pipes. Mention has been made in Chapter VII of an alternative method of manufacture in which the iron is “spun” by centrifugal force against a rotating mould, no core being used in this process. B.S. No. 78 specifies vertically cast-iron pipes for pressure pur- poses and B.S. No. 487 similar pipes for drains. B.S. No, 1211 specifies spun iron pipes for pressure purposes. ‘The fittings to be used in conjunction with cast-iron drain pipes are dealt with in B.S. 1180. Wrought-iron Pipes. Wrought-iron pipes are made in three alternative ways. The strongest pipes, such as high-pressure hydraulic mains, are formed by winding a bar of iron spirally around a core, the abutting edges being then welded together. Pipes of this variety are of very great strength, and have been made to stand a stress of several tons per square inch without injury. The second method is that adopted for pipes of gas strength and consists of bending a bar round a core and then welding together the abutting edges, thus forming a longitudinal joint. Such a pipe should not be used for other than gas. The third method is similar, but the adjoining edges are lapped and welded instead of being merely butted together. This class of pipe is what is known as water strength, 428 THE MATERIALS USED IN SANITARY WORK Protection from Corrosion. As has been pointed out in earlier chapters, it is necessary to protect iron pipes from corrosion. The Angus Smith, galvanising and Bower-Barff processes have already been described. Another process is that of glass enamelling the inside of the pipe. This consists of coating them internally with lead glaze, as described for stoneware, and then firing them ina kiln. The great trouble with pipes of this kind is the difficulty of cutting them without removing part of the internal lining of glass and so exposing the iron to oxidation. Steel pipes are specified in B.S. No. 534. Lead. This material is of great importance in sanitary work. Not only is it used for gutters, flashings, flat roofs, cisterns, damp courses, etc., but it is the material of which most of the pipes in a house are often formed. Lead is produced by smelting ores, the ores from which it is principally obtained being galena and cerussite. It is a very malleable material and can be readily worked to almost any shape without applying heat. Sheets of lead can be either cast or milled. Cast sheets are not often used, having several drawbacks. They can be obtained up to about 16 feet long by 6 feet wide, but are of uneven surface and thickness and liable to flaws and sand holes. Milled lead sheets are generally used both for flats and gutters, and also for all other sanitary work. They are obtained by first casting a large, thick block and then rolling and re-rolling it in a mill, having two very heavy steel rollers, until it has been reduced to the desired thickness. Part way through the operation, the sheet which is in process of formation is cut up into parts these parts being dealt with separately. Milled lead is obtainable in sheets up to about 35 feet long and 9 feet wide, though rather smaller sizes are more usual. As previously stated in another chapter, milled lead is described by its weight per superficial foot. The Standard Speci- fication for sheet lead is B.S. No. 1178. Ternary Alloys of Lead. One defect of lead is that under long continued strain, especially when subjected to vibration, it erystal- lises and becomes brittle. It has been found that this does not occur if the lead is alloyed with small quantities of certain other metals, and the resulting alloy is considerably stronger than ordin- ary lead. These alloys are known as “ternary alloys” and refer- ence has been made to them in Chapter VII. Red and White Lead. Lead is also used in sanitary work in quite a different form from the foregoing; that is to say, in the form of red and white lead, as used for jointing in certain cases. Red lead THE MATERIALS USED IN SANITARY WORK 429 is obtained by oxidising metallic lead in a furnace, by exposing it to the action of air. A coating of oxide is formed, and this is removed to expose a fresh metallic surface, this process being con- tinually repeated. The oxide is then ground in water between stone rollers, and again exposed to the action of air in another furnace, which permits it to take up more oxygen and gives it its red colour. It is then re-ground in water and dried. White lead is made by exposing metallic lead to the action of the fumes of acetic acid in the presence of carbonic acid gas. The lead is sus- pended in jars over the acid and