Roman cement

“ Roman cement mortar should consist of one or one and a half parts of cement to one part of sand. Selenitic lime mortar is usually in the proportions of one to four or five, and must be mixed in a particular manner, the lime being first ground in water in the mortar mill, and the sand gradually added. Blue or black mortar contains equal parts of foundry ashes and lime; but is improved by the addition of a proportion of cement. For setting fire-bricks fire-clay is always used. ”

“ When a bone is too imperfect to be united as a whole, it may be imbedded in Roman cement, or plaster of Paris, which when dry may be coloured of the prevailing tint of the rock. For large heavy specimens, the cement is preferable; it is of easy application, and the fissures and cracks of the bones may be filled up with it, taking care first to cover the parts with thin hot glue, or the cement, when it dries, will shrink and fall out. ”

“ The common cement used in building, which is called mortar, is made of sand and quicklime mixed with water. Roman and Portland cements consist of certain kinds of clay burnt and ground. Plaster of Paris forms a useful cement, it is to be mixed with water to the consistence of cream, and it hardens in a few minutes. Glue is an invaluable cement for wood and many other purposes, it also joins any kind of broken glass or china that will not have to be subjected to much wetting. Shellac dissolved in spirit is a useful cement ”

“ The employment of Roman cement, plaster, &c., for masonry work, hardly comes within the limits of Domestic Manipulation.
2504. Cement for Leather and Cloth
An adhesive material for uniting the parts of boots and shoes, and for the seams of articles of clothing, may be made thus:—Take one pound of gutta-percha, four ounces of India rubber, two ounces of pitch, one ounce of shellac, two ounces of oil. The ingredients are to be melted together, and used hot.
Go to Bed with the Lamb and Rise with the Lark.
2505. Birdlime
Take any quantity of linseed oil, say half a pint ”

“ The mortar also was such as may be usually found in mediæval buildings, but presented none of the characteristics either of Roman mortar or Roman concrete. Nor were there any such unmistakable substances found attached to the tiles, the rubble, or the stonework which made up the section of the City wall. Roman mortar is not easily mistaken; so hard and so durable is it that it is frequently easier to break the stones themselves than the cement which holds them together. ”

“ The lime, in the state in which it comes from the kiln, is first ground to powder, and is then mixed with sand and gravel, and chippings of stone. The purposes for which the mortar is required indicate the coarseness and quantity of the intermingling gravel. When wanted as concrete, to form, independently of other materials, the foundation of some heavy structure, stony fragments of larger size are mingled with the lime than when the mortar is to be used to cement chiselled stones, or even than when wanted to constitute with rubble the interior of a wall. ”

“ The most characteristic constituent is the oxide of iron, which gives the cement a reddish colour, and the presence of manganese also differentiates Roman from Portland cement, which rarely contains appreciable quantities of that element. The high percentage of alumina causes the cement to be quick-setting, and it becomes hard in about five minutes. It resists the action of water, salt or fresh, very well, and is therefore useful in situations where the work is likely to be submerged immediately after it has been put in place. ”

“ The cement is white lime, and the layers are much thicker than is seen in any of the burnt brick edifices at Babylon; approaching nearer to the style of the Greek and Roman masonry found among the ruins of Alexandria, where the layers of lime are almost as thick as the bricks themselves. At Babylon the cement is scarcely perceptible. The symmetry of the work bears considerable resemblance, however, both to the Birs and the fine fragments of brick-masonry of the age of the Caliphs, still remaining at Bagdad. ”

“ When mixed with lime it forms a very strong hydraulic cement, of equal use in concrete, mortar or undercoats of stucco. It is to this material that the concrete walls of Rome owe their enormous strength and durability, in many cases far exceeding those of the most massive stone masonry. ”

“ Concrete (opus caementicium, Vitr. ii. 4, 6, 8) , the most important of all the materials used, is made of rough pieces of stone, or of fragments of marble, brick, &c., averaging from about the size of a man's fist and embedded in cement made of lime and pozzolana-forming one solid mass of enormous strength and coherence. Stucco, cement and mortar (tectorium, opus albarium and other names) are of many kinds; the ancient Romans especially excelled in their manufacture. ”

“ Fancy for a moment the difference for the worse, if all the grim, browned, rotted walls of Rome, with their peeling mortar, their thousand daubs of varying grays and yellows, their jutting brickwork and patched stonework, from whose intervals the cement has crumbled off, their waving weeds and grasses and flowers, now sparsely fringing their top, now thickly protruding from their sides, or clinging and making a home in the clefts and crevices of decay, were to be smoothed to a complete level, and whitewashed over into one uniform and monotonous tint. ”

“ The Italian method is to spread on the wall a thick coating of mastic cement composed of marble dust or powdered stone, lime, and linseed oil; when this cement is partly set a coating of fine plaster is laid on the top and brought up to the level of the intended surface of the mosaic; the design is traced on this surface, and the plaster is then cut away with a fine small chisel, little by little, just sufficient at a time to receive a small quantity of the tesseræ or cubes, which are first dipped in moist cement and inserted in their proper places, matching the colour copied from the cartoon. ”

“ The chocolate-brown earth imported from Pozzuoli or dug from beds in the campagna, is known as pozzolana, and early in the history of Rome her builders discovered that when mixed with lime it made a remarkably strong cement. As such they used it for foundations, for the lining of walls and ceilings. With pieces of brick and stone a concrete was formed which was poured in a liquid state between wooden casings, and when set proved to be one of the hardest and most durable of the materials used. ”

“ The other mark is the peculiar cement with which the wall is lined, called Opus Signinum in Latin, Coccio Pesto in Italian, which is made of broken pottery, and is the hardest cement that is known; it is often impossible to break it, even after it has been exposed to the weather for centuries.
A plan and section of the ground between the two gates, called by Frontinus Esquilina (S. Lorenzo) and Viminalis (Maggiore) , shew the difference of level, and the three aqueducts passing underground in the middle between the two gates, and carried on arches at both ends near the gates (see No. 1938*) . ”

“ The secret is not in the bricks or the stone, but in the cement and mortar, neither of which essentials can we make as the ancients made them.
In modern buildings the cement and mortar are the weakest points; in the buildings which the Romans and Greeks raised thousands of years ago the cement and mortar are the strongest points, and hold good while the very stones they bind together crumble away with age. We cannot, with all our science, make such cement and mortar, and therefore we cannot build such buildings as the ancients raised. ”

“ Among operatives and artists, any cement used to fill up holes and to cover defects in their work. Among statuaries, a mixture of plaster and free-stone is commonly used for this purpose; among joiners and carpenters, a mixture of sawdust and glue, or of whiting and glue; and among coopers, one of tallow and chalk. The name is also given to a stone-coloured mixture used for the fronts of houses, and said to be composed of wood-dust and lime, slaked together, stone powder, and a little ochre, umber, or sienna ”

“ If a long nail or rod or strong stick is placed in the center of this mass, it can serve the purpose as an axis to a templet which will form the contour of the jardinière when moved around in a circular direction. The metal must be good and heavy and sometimes it is necessary to reinforce the templet with wood.
After the clay form is built, cases are made in several sections from the plaster the same as for small forms; and cement and concrete used in large quantities after the same method as for small forms. ”

“ The result is that the mortar so made sets rapidly, and is very hard.
It is claimed that a larger proportion of sand can be used with selenitic lime than with ordinary, thus counterbalancing the extra expense occasioned by royalty under the patent and special care in mixing. When a limestone contains 20 to 40 per cent, of clay, it becomes what is called a cement, and its behavior is different from that of limestones with less clay. Ordinary limestones are, as you know, calcined in a kiln. ”

“ All square joints should be first prepared by raising a fibre, as in veneering work. Apply the cement hot, as glue is spread. In a few hours the solvent will evaporate; then heat the parts sufficiently to melt the cement; press together firmly. The gutta-percha will be found to be an excellent cement for all leaky places in stone, brick or wood work. Mix it with sand, or any fibrous substance, apply hot, or melt it in with a hot iron. The pure gutta-percha will cement broken stone, marble or brick, so firmly that it will remain for years. It is undoubtedly the best cement ever yet discovered. ”

“ After the raw material has been burned thoroughly and is taken from the kiln it looks like little cinders or clinkers about the size of marbles. The cement clinker is then cooled and ground to a powder, after which it is stored away for a little while to season.
The first Portland cement ever made in the United States was turned out by David O. Saylor, of Coplay, Pa., in 1875, but the development of the new industry was very slow, as builders and engineers seemed to be blind to the great possibilities of the material that built Imperial Rome. ”

“ Such hand-built ware does not, of course, include the large painted kraters and amphorai of Athenian make; for these have all the ear-marks of wheel-thrown pottery. Wooden cores are still used today in the making of cement forms. Since the clay cement shrinks upon drying and the wood does not, care must be taken to prevent the former from cracking. The wooden core is therefore made in collapsible form. A wedge is made in the center and a core built around it. When the work is finished the wedge can be drawn out and the sides of the core will fall in. ”

“ And even then it is reckoned a hot and forcing manure, chiefly fit for cold and wet lands. The principal use of lime, however, is as an ingredient in mortar. This, you know, is the cement by which bricks and stones are held together in building. It is made of fresh slacked lime and a proportion of sand well mixed together; and, when used for plastering walls, some chopped hair is put into it. The lime binds with the other ingredients; and in length of time, the mortar, if well made, becomes as hard, or harder, than stone itself. ”

“ For glass, earthenware, porcelain, and all kinds of stoneware, these cements are excellent. A cement for glass and marble is prepared by rubbing together one part of fine pulverised glass, and two parts of pulverised fluorspar, and then adding enough waterglass solution to give it the consistency necessary in a cement.
Waterglass mixed with hydraulic cement to a thick dough makes a good cement for the edges and joints of stone and marble slabs. It is well to mix but little at a time, as it hardens very quickly. ”

“ We know that metal craftsmen{60} often roughen the surface of metal where enamels are to be placed and fired in, to insure more perfect attachment, and a similar treatment to the cement will do likewise for the cement color. When the cement tile has been removed from the water and surplus moisture shaken off a little plain neat cement is placed on the surfaces to be colored and to this the color in thin paste form is dripped from a brush. No back stroke is possible without injuring the finish. ”

“ There are various minor external causes for the failure and ultimate destruction of cement mortar and concrete, but their discussion is a matter for the specialist. Failure from inherent vice in the cement has been already touched on; it can always be traced to want of skill and care in manufacture.
Calcium Sulphate Cements.—Under this term are comprehended all cements whose setting properties primarily depend on the hydration of calcium sulphate. They include plaster of Paris, Keene’s cement and many variants of these two types. The raw material is gypsum (q.v.) ”

“ A strong base for a cement for glass, as well as wood or stone, is made by gradually stirring finely sifted wood-ashes into silicate of soda, or strong acid glue, till a syrup-like substance results. In America the best ashes for this purpose are those of the hickory. Perhaps beech wood yields them equally good.
There is a Diamond Cement which is of special value to attach gems to rings or metal, to make coral or pearl or ivory adhere together, and, in short, for all fine work where a very strong adhesive is required. ”

“ Slag and cinder concretes are for this reason given minor consideration in this volume.
BROKEN STONE.—Stone produced by crushing any of the harder and tougher varieties of rock is suitable for concrete. Perhaps the best stone is produced by crushing trap rock. Crushed trap besides being hard and tough is angular and has an excellent fracture surface for holding cement; it also withstands heat better than most stone. Next to [Pg 14] trap the hard, tough, crystalline limestones make perhaps the best all around concrete material; cement adheres to limestone better than to any other rock. ”