« PreviousContinue »
clear. I do not think much is to be gained by making the pipes less than 5′′ in. diameter and, on the other hand, a greater capacity is certainly not required for the purposes of an ordinary household. I therefore look upon it as a useful dimension for ordinary cases.
As there is an absence of hydraulic pressure in cast-iron pipes used for the conveyance of ordinary house-drainage, no extra thickness of metal is required on that account, and they may therefore be made thinner than ordinary street mains. The following is a table of the thickness and weight of pipes of different diameters suitable for the purpose.
In practice, I believe, pipes 5-16ths of an inch in thickness are sufficient for drainage purposes, and this would give about 100 lbs. as the weight of a 6 ft. length of pipe, 5 in. diameter.
Among the various kinds of joints that known as the socket joint' appears to me to be the best suited for iron house drains, and although the pipes themselves may be made lighter than main pipes, the socket should not be reduced in weight or strength because they are subjected to the same strain from the staving of the lead. Great care should be used in this respect, the more so as workmen may be employed who are not so experienced as those in the service of water companies.
A joint has been brought under my notice which has been patented by Mr. Eaton, C.E. It is intended for the use of Spence's metal or sulphur, and consists of an eccentric ring with a pouring hole on its top side. This overlaps the joint on both ends, and would be useful I think where it was required to insert a length of pipe between two already in position, as this could be done without the necessityof lifting more than the piece which was to be removed. The North British Plumbing Company have carried out work upon the plan shown at the National Health Society's Exhibition under my direction for Mr. Wills, M.P., in his house at Hyde Park Gardens. The cast-iron air chamber floor which was exhibited is an effort to simplify the arrangement now so frequently adopted with advantage of having a manhole with a floor composed of half pipes as a channel for the passage of the sewage and a trap beyond it to cut off the drain from the main sewer. In the cast-iron substitute | for this appliance the mouth of the trap is practically extended so as to form a floor for the manhole in ❘ itself, and this extension has the advantage of affording a provision for side inlets for the passage of surface water and for other purposes. At the same time provision is made for a cleansing eye towards the sewer which is fitted with a brass plug.
The formulas which are commonly used for calculating the velocity of water in pipes running full must be considerably modified for the flow of house-drainage in 5-inch pipes. Taking
At the further or house end of the drain, instead of building a shallow manhole a cast-iron terminal is provided which is easily accessible and made secure by means of a similar plug to the one in the front just spoken of. In making a connection between a lead soil pipe and an iron socket, it is well to have a strong copper piece with a brazed lap seam slipped over the lead pipe and securely soldered to it. This allows for an oakum and red lead joint to be made with sufficient substance to admit of caulking. As regards the comparative cost of iron and earthenware for house drains, it must be borne in mind that a great proportion of the total expense of lifting an old drain and laying a new one is common to both systems. For instance the cost of excavating, filling in, and making good is practically identical. The time occupied in making good the joints of an earthenware drain is as six to one as compared to an iron drain, the number of joints being as three to one in the case of 2 feet lengths of stoneware, and 6 feet lengths of iron, and I consider the time occupied in each as two to one in favour of the metal. This nearly balances the extra cost of the material. The connections, including the air chamber floor, are more costly than earthenware, but this, in the case of an ordinary London house drain should not amount to more than 57. in all. I think that the greater security to be obtained from the use of cast iron quite justifies the expenditure of the additional cost, and this will hold good so long as cast iron is to be obtained at its present price.
I shall now say a few words about the other kinds of materials used for house drains, omitting bricks as obsolete. The practical objections to the use of earthenware pipes are, 1st, their liability to twist in firing. (Mr. Ernest Turner, in his excellent book Hints to Househunters,' speaks of having rejected as many as 60 per cent. of pipes 'sent from wellknown manufacturers'); 2nd, their liability to fracture. Concussion, without fracture of the surface, is often sufficient to detach a branch piece from a pipe in which the material seems to be continuous, although the connection is often secured by little or nothing but the glazing. As such a contingency may delay a squad of workmen for several hours until another pipe and branch has been obtained, there is a temptation to make use of defective pipes. Experience shows that workmen are not above yielding to the temptation of concealment. Broken bends and bad connections are frequently found in places which are most available for the passage of sewer gas into a dwelling. 3rd. The short lengths in which earthenware pipes are made necessitate an excessive number of joints in order to make up the length of an ordinary house drain. The joints when made with clay are inefficient, and when made with cement are subject to many drawbacks which nothing but great and uncommon pains on the part of the workmen can overcome. The projection of cement to the interior of the joint is a necessary condition, and this must be removed. In doing so the pipe is liable to movement during the critical period when the cement is setting. The position of a pipe at the bottom of a deep cutting renders it difficult to pack the joint from the bottom. Only a small proportion of earthenware house drains are found to be tight when tested with a pressure of even a few inches head of water. These are among the considerations which have led me to adopt iron in preference to other materials, and I shall be glad if this paper has the effect of calling further attention to the subject.
BY JOHN SLATER, B.A.
Fellow of the Royal Institute of British Architects.
II. BRICKS AND MORTAR.
THE geological nature of a country always determines the character of its buildings. Where good natural building stone is abundant it is sure to be quarried and used, but where this does not exist recourse is had to some artificial material which will take its place. The material which has been more extensively used than any other is brick, the manufacture of which dates from the most remote antiquity of which we have any record.
Herodotus relates that the walls of Babylon were constructed of this material, and there are numerous very interesting pictorial representations of brickmaking and brick-laying in the hieroglyphic literature of ancient Egypt which has been preserved to us in stone blocks and mural tablets. Moreover, the existing ruins of some of the most ancient monuments of Egypt have enabled modern explorers to obtain specimens of bricks which must be several thousand years old, the great care taken in their manufacture and the extreme dryness of the climate having tended to preserve them. For instance, there is at Memphis a pyramid still partially standing built entirely of brick, and it is very probable that this was erected by Asychis, who succeeded the son of Cheops, the builder of the Great Pyramid. It is probable that burnt bricks, such as were used in this pyramid, were the exception, and that Egyptian bricks were for the most part sun-dried only, nearly all the common dwellings being constructed of this material, but burnt bricks were occasionally used.
In Assyria, also, sun-dried bricks were very largely used, the huge mounds upon which the palaces were erected being thus built, and the walls of the palaces themselves having a brick backing faced with alabaster. But the recent researches of M. Botta and M. Victor Place have resulted in the discovery of some admirable examples of Assyrian brickwork of burnt bricks, the most interesting being the arched gateway of the entrance to the palace of Khorsabad, which, both in materials and execution, would do no discredit to the best modern builder. The archivolt of this gateway is formed of wedge-shaped burnt bricks, which are enamelled in six different colours. Vitruvius mentions three kinds of bricks as having been used by the Greeks, called didoron, tetradoron, and pentadoron; these differed only in size, and were more like tiles than our bricks. The two latter kinds were square on plan, and Vitruvius says that those called tetradoron were used for private buildings, the others for public. Roman bricks differed considerably in size: they were frequently square, and in thickness rarely exceeded an inch and three quarters the clay was evidently well tempered, and the bricks thoroughly burnt, the surfaces being in many cases scored deeply in order to form a key for the mortar. The Romans carried the art of brickmaking to very great perfection, and used this material for nearly all their principal buildings, employing it as a backing to their walls even where more costly materials were used for facing. They introduced brickmaking into the various countries which they conquered where suitable earth was found, among others into England, and frequent remains of Roman brickwork still exist in fact so good were their bricks, that in numerous instances
they have been re-used in later work. St. Alban's Abbey, which was built in the latter part of the eleventh century, is a good example, a very large number of bricks used in its construction having been taken from the ruins of the old Roman city of Verulam. The art of making bricks in England seems to have languished if not to have died out altogether from the time of the departure of the Romans until towards the end of the thirteenth century; the oldest existing example of brickwork being Little Wenham Hall in Suffolk, which was built about 1260. In the time of Henry VIII. brickmaking had considerably developed, and very elaborate mouldings were executed which were probably copied from some of the specimens of brick architecture which are to be met with in many parts of the low countries. The seventeenth and eighteenth centuries afford many excellent examples of moulded brickwork, and the number of bricks made in this country kept on increasing until the manufacture received a temporary check at the end of the last century by the imposition of a tax, which varied at times from 2s. 6d. to 5s. 10d. per thousand until it was entirely repealed in 1850. Since that date the manufacture has developed very largely in consequence of the great increase in building operations, and the number now made annually in this country cannot fall far short of ten thousand millions.
The subject of bricks and brick-making is a very wide one, and it would be obviously impossible to treat it fully in a short article. The number of different kinds of bricks is so large, the processes of manufacture vary so widely in different parts of the country, and the scientific principles underlying these processes-involving, as they do, a wide knowledge of physical science-are so complicated and so little understood that several volumes might easily be written on the subject. I shall merely attempt to describe briefly what are the qualities of a good brick, and upon what these qualities depend, and to point out the sanitary evils which result from the use of such bricks as are too frequently employed in the erection of those suburban villa residences which are the mushroom growths of the happy hunting-grounds of the speculating builder.
A brick is not an ultimate fact of nature, but its qualities as a building material depend upon the constituents of the earth from which it is made and the manner in which this earth is prepared, dried, and burnt. It is frequently imagined that a brick is simply a rectangular piece of burnt clay; but the varieties of clays are very numerous, and, as a matter of fact, it is extremely rare to find natural earths suitable for brick-making nearly all require the admixture of sand, loam, chalk, or other substances.
Brick-earths may be divided into three classes, clays, marls, and loams. These all contain silica and alumina, and generally a trace of oxide of iron.
Among the natural earths suitable for bricks is that mild alluvial clay or marl which used to be found near London combined with a calcareous substance called 'race.' This clay produced the fine yellow malms which give a special character to London brickwork of the early part of the century.
The marls have a considerable portion of lime mixed with them, and the loams are light, sandy clays with an excess of silica: firebrick clays are almost entirely free from lime, magnesia, &c. All these constituents are chemically combined, and it is a curious fact that it has hitherto been found im
possible to mix artificially the component parts in the same proportions in which they exist naturally, and to obtain that quality of plasticity which is in the natural substance.
Pure clays are nearly always too strong for brickmaking, and require to be mixed with milder earth, and the loams are so sandy that the admixture of lime is required in order to bind together the siliceous particles.
quite rotten, and falls to pieces at a single blow. This kind of brick is called a shuff, and if it is attempted to use such in a building damage is sure to result. During the drying process the bricks have to be protected from frost and wet. The next operation is burning, and London bricks such as have just been described, in which the breeze is mixed with the earth, are always burnt in a clamp. A clamp is an erection formed mainly of the raw bricks to be burnt, cased in and partially supported by burnt bricks. The raw bricks are placed in layers slightly inclined towards an upright wall in the centre of the clamp, and between each layer of bricks is one of breeze or cinders, the latter being thicker at the bottom of the clamp than at the top. Open flues are left at intervals which are filled with faggots for the purpose of firing the clamp, and after these have been ignited and the breeze is well alight the openings of the flues are stopped up with clay, and the whole mass burns until the breeze is all consumed. The courses of brick are laid on the incline, and not horizontally, in order that as the breeze burns away there may be no tendency for the bricks to fall outwards. It is manifest that in this method of burning it is quite impossible that all the bricks should be equally burnt, those near the cutside being underburnt, and those close to the flues, where the draught is greatest, being frequently completely fused. The former are called place bricks, and should never be used for outside work, or in situations where they are subject to great pressure, which they are not calculated to resist the fused bricks are called burrs or clinkers, and are extremely hard; they may safely be used for foundations, if not too irregular in shape, but are of course not suitable for facings. Between the two extremes of place bricks and clinkers there are many gradations in the bricks from the same clamp, and they are sorted out and sold as malms, seconds, &c. It is frequently imagined that the variations in the quality of bricks when burnt are owing to differences in the making, but in nine cases out of ten these are due solely to the burning.
As the natural marls became exhausted, some one-it is not known who-discovered the possibility of making an artificial marl or malm by mixing chalk and clay together, after thoroughly washing them and reducing them to pulp, much in the same way as in the preliminary process of making Portland cement; and this process is now very largely adopted for the best bricks in the neighbourhood of London. The general routine of brickmaking is as follows:-The ordinary brick-earth is dug in the autumn, and turned over so that it may be broken up by the frosts of winter. It is then laid on a hard floor, and 'malmed' in the spring; that is, the liquid artificial malm, made as above stated, is conducted on to the earth and covers it completely. The proportion of malm to brick-earth depends entirely upon the nature of the earth. The whole mass is left to settle for some weeks, and it is then 'soiled' that is, covered with fine sifted ashes; and this operation is a very important one, as upon the proportion of ashes to the whole bulk of earth the quality of the brick when burnt will mainly depend. No general rule can, however, be laid down, as very much depends upon the nature of the material itself, also upon its state of humidity and upon the meteorological conditions of the atmosphere at the time of mixing. A very large amount of actual experience is required, and it frequently happens that the individual who has this experience is unable to impart it to others.* After soiling, the heap is again left undisturbed till the moulding season commences, when it is tempered-that is, turned over with a spade and watered to bring it to a proper consistency, after which it is thrown into the pug mill and thoroughly kneaded together when it is ready for moulding, in which process a small quantity of sand is mixed with it, and it is formed by hand into the size and shape of an ordinary brick. Now all these processes, which have been briefly described, have to be conducted with great care. The clay is hardly ever found without pebbles, and if means are not adopted for screening them off or crushing them they will become imbedded in the brick, and will cause it to crack during burning; if the chalk is not thoroughly ground up, unslacked nodules will find their way into the bricks and will eventually slack and blow the brick to pieces; if the tempering in the pug mill is not well done the bricking mill, but for ordinary kinds the tempering is done will not be homogeneous; and if the moulder does not press the clay well and uniformly into the mould it will when burnt lack density, and probably be very porous. Equal care has to be given to the next process, which is that of drying the bricks in hacks before burning, and it is this stage that probably is most neglected. A considerable proportion of the contained water must be evaporated before it is safe to burn the brick, and if this is not done it turns out
A similar peculiarity has been noticed in the case of men who are accustomed to mix colours for dying purposes, the proper proportion of the various tints being very important; and often the best mixers use no measures at all, but are able to tell by a species of instinct the amount that is required to bring about the desired result,
In the provinces generally the processes of digging and turning over the brick earth are carried on much in the same way as in the London brick-fields, but in many cases the earth is very hard, and contains lumps of limestone, and here the process of grinding and crushing the earth is resorted to. This is an excellent practice so long as ordinary care is used in the selection of the earth, but just as is found to be the case when a mortar mill is used for grinding and mixing mortar, there is a strong temptation to use almost any earth, whether suitable or not, and the consequence is that bricks are frequently turned out that are quite worthless. For the best class of bricks the earth is passed through the wash
by treading and by the spade, as in the London district, but no breeze or fuel is mixed with the earth, and this constitutes the principal difference between the stock brick and other kinds. The tempered earth is moulded and dried in the usual way, and the bricks are then burnt, or rather baked, in a kiln or oven, which is in some districts rectangular in shape and in others circular, with a domed top. Arched fire-holes are formed opposite each other and connected by flues formed of the bricks which are to be baked the number of the fire openings depends upon the size of the kiln, which varies considerably. The arrangement of the bricks in the kiln is a work of some skill, as care must be taken that the heat
should be able to pass all round each brick, and that there should be a proper draught throughout. Coal is used for fuel, and fires are made up in the various fire-holes, and the heat applied very gradually, in order that the steam may be driven off before the actual baking commences. When the full heat is attained the top and all openings are carefully covered over with clay or turf to avoid unequal draughts, and a steady heat is kept up for a time, which varies according to the nature of the brick-earth and the kind of brick which is to be burnt, after which time the fires are extinguished and the kiln is allowed to cool. The same thing happens with kiln-burnt bricks as with those burnt in a clamp, viz., that different qualities are taken from the same kiln, the bricks that are close to the fire always becoming partially vitrified and nearly black, and those which are under-burnt being usually of a mottled colour.
the proper shape. They either force out, through a suitable mouthpiece, a continuous column of pressed clay of the proper width and thickness, which is cut by wires into the required brick sizes as it is pressed out from the machine; or press the clay into a mould of the exact size of the brick which is then discharged from the mould on to a table. The former class of machine is a very useful adjunct to a brickfield, where the clay is free from stones, and uniform, but where this is not the case, and also for stock bricks, it would be quite useless, as the cutting wires would drag out the particles of stone or breeze, and the face of the brick would not be even. The pressed bricks made by a machine, as a rule, have extremely sharp arrises and even faces, but it frequently happens that some time after being used in a wall the outer face flakes or chips off. This is probably due to the fact that the extra pressure of The exact tint which properly baked bricks the machine is not transmitted entirely through the assume depends in the first instance upon the nature moist brick, which is thus not quite homogeneous, of the clay, which, if pure, and combined with silica the outer surface being denser than the interior, only, would always burn of a pure white, but as consequently there is great risk of the interior not nearly all clays have in their composition a varying being sufficiently dried before the brick is taken to quantity of metallic oxides, these give all the grada- the kiln, and if this is the case the brick is certain tions of colour which are met with in bricks. If not to last. oxide of iron is present in very small quantities, the resulting tint will be a light tawny yellow so long as the heat of the kiln is not too great. If there be a small proportion of silica and a large quantity of oxide of iron, the favourite red colour is produced. The presence of lime changes the red colour due to iron to a creamy brown. Where oxide of iron is combined with a small quantity of oxide of manganese a black tint results; and clays naturally burning red will turn yellow by the admixture of a fusible white sand. In all cases, however, the final tint of the bricks depends to a very large extent upon the conditions of burning. For instance, in the case of many of the Staffordshire clays, an extra two hours' firing converts red bricks into blue ones, and it is upon an accurate knowledge of these conditions gained by practical experience that the production of any desired tint depends, and its uniformity is secured. The great faults of ordinary kilns are that the fuel is used uneconomically, and that a considerable amount of heat is wasted during the cooling of the baked bricks. These faults have been remedied by the invention of the Hoffman kiln, which is arranged in compartments, so that all stages of burning, from the filling in of new unburnt bricks to taking out the finished ones, can be proceeded with simultaneously. Besides this, the air supporting the combustion of the fuel is gradually warmed by passing over chambers containing the bricks which are cooling until, on its arrival at the burning chamber, it has almost the temperature of the furnace itself, and from this point it is again taken through another series of chambers and utilised for drying the new bricks before passing up the chimney shaft. An arrangement of dampers allows any chamber to be shut off at pleasure, so that practically there is no necessity for allowing the fires to go out at all, and the cost and delay of rekindling are avoided.
Of late years, in places where a large number of bricks are made annually, machinery has almost entirely superseded hand labour in brick-making. Brick machines may be briefly described as of two kinds; first, those which act upon the moist clay after tempering. These consist of a pug mill for tempering the clay, and a means of moulding it into
The second class of machines operate upon clay which is nearly dry, and in these much greater pressure is used than in those which act on the moist clay; in fact some of them are capable of exerting a pressure of between 300 and 400 tons. The clay, before being placed in these dry machines, must be very finely pulverised, and they must therefore be used in combination with a powerful set of crushers for producing this result. In one such machine the clay, after being crushed, escapes into a receiver, from which a band, with small buckets attached, carries it to the hopper of the moulding machine, where it is powerfully compressed by the moulds and turned out in the proper shape. These dry clay machines produce a denser brick than the others, and, moreover, there is a considerable saving of time through their not requiring drying before being burnt. There is, however, great danger that the air which collects between the small particles of the crushed material will not be thoroughly driven out, and in this case the brick would be seriously injured by the expansion of the air during burning. One machine has been constructed so as to give several distinct squeezes at intervals, with a view of obviating the difficulty.
Various patterns of moulded bricks of a red or white colour are now made by different manufacturers, among whom may be mentioned Rosher & Co., the Hartshill Brick & Tile Co., the Bracknell Pottery Co., and Messrs. Brown, of Braintree. The latter firm have some extremely artistic patterns which they keep in stock, and their bricks are, as a rule, of excellent quality, the figures being very sharply cut. Figs. I to 4, p. 6, show some of their moulded bricks, which afford a very cheap means of obtaining architectural effect in the elevations of brick buildings. For obtaining the same effect with more originality of design, some excellent red rubbers and cutters are made by Mr. Lawrence, of Bracknell, and these can be worked by hand into any desired pattern.
Bricks with an enamelled face in various tints have recently been manufactured, and at the recent Building Exhibition some good specimens were shown by the Bourtree Hill Colliery Company. This enamelled face is given by applying to the surface easily fusible
salts, such as the silicates and borates of sodium, &c., to which metallic oxides are added if colour is required, and if the bricks be burnt at a sufficiently nigh temperature, the enamel becomes thoroughly incorporated with the clay, which for this purpose must be a species of fire-clay.
The characteristics of a good brick are-1, that it should be regular in shape, in order that the pressure upon it should be equal over all its surface; 2, that it should be tough and not brittle, so that when a building is being erected, there may not be a very large proportion of bats and half bricks caused by the labourers shooting down the bricks from their hods; 3, that it should have a clear metallic ring when gently knocked against another brick; 4, that when broken it should show homogeneity of structure; and, 5, that it should absorb little water. This is the most important characteristic of all, and one that could be very easily tested, though it is often quite neglected. If a brick absorbs much water, the walls of houses built with it will, during many months of the year in damp climates, never be dry at all, and the warmth of the interior will certainly have a tendency to draw the moisture into the house, the consequence being that wall papers will be soiled, and the rooms rendered damp and unhealthy. Moreover, in winter, frost will find its way into the interior by the bricks, and will tend to break them up. No bricks can be obtained for ordinary housebuilding that do not absorb some water, but the amount should never exceed from 10 to 15 per cent. of the volume of the brick, and those bricks
should be preferred which absorb slowly, for as a rule it is found that the rate of absorption of water is in inverse ratio to that of parting with it, so that a quickly absorbing brick will lose its water very slowly; it is needless to dilate on the disadvantages of such a characteristic.
About fifteen years ago the Manchester Society of Architects issued a report upon brick-making which contained some valuable recommendations to brick manufacturers, one of the most important being that moulds should be adopted in different brickfields which would ensure the bricks when burnt being of one uniform size. This is supposed to be the case now, but as different earths contract differently, it frequently happens that the bricks from different fields differ both in thickness and width, and great difficulty is thus occasioned in making the courses regular, where one kind of brick is used for facing and another for backing. It would be too much to he hoped that the present size of bricks will be generally altered, but for many reasons a longer and thinner brick would be preferable, and for very good work an architect will occasionally have bricks specially moulded; but of course this is impossible for ordinary buildings.
The whole subject of bricks and brick-making has not received the attention it deserves, probably because the opinion was long held that stone must be used for any important building. For London, however, or any other smoky city, brick is a tar preferable material, and now that such eminent architects as the late Mr. Street and Mr. Waterhouse have shown with what artistic effect brick can be employed, we may hope that the subject will be neglected no longer.
Although, strictly speaking, the quality of the mortar in which bricks are laid has no necessary connection with the bricks themselves, yet as bricks are never used except when built into walls, and as the quality of brickwork depends very largely upon the kind of mortar used, a few works on this material may appropriately close this article. All that was stated in the description of concrete as to the necessity of using a good cementitious material, such as ground stone lime or Portland cement, in preference to chalk lime, applies equally to mortar. In districts where chalk lime is plentiful and used for mortar, buildings are never found to stand well when exposed to the weather, as the rain gradually washes out the mortar from the joints. It is also essential that the sand used should be clean and sharp and free from loam or earthy matter. If the sand found in the locality is not very sharp, the mortar would be greatly improved by mixing with it a certain proportion of pulverised coke or smith's ashes. If black mortar is required, the latter should be used as the colouring matter; but builders find it much cheaper to use lampblack, which always deteriorates the mortar. The exact quantities which should be used of the various ingredients depend somewhat upon their quality, but as a general rule three of sand and one of lime makes very good mortar. It is very essential that all the ingredients should be thoroughly mixed up and incorporated together; and the lime should be well ground, as otherwise small unslaked nodules will find their way into the mortar, and will blow-that is, swell in slaking-and damage the mortar after it has set. A mill is now frequently used for mixing mortar; and there is no doubt that very good mortar can be thus made with materials that could not be used if only