Rudimentary treatise on limes, cements, mortars, concretes, mastics, plastering, etc

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Preface

The object the author of the following treatise has proposed to himself has been to put into as condensed a form as was consistent with the nature of the subject the knowledge and information dispersed through a numerous collection of authors who have treated thereupon. They are mostly in foreign languages ; for it is much to be regretted that our own scientific authorities have not thought it worth their while to occupy themselves with this highly important branch of practical chemistry.

The author has endeavoured, as conscientiously as possible, to avoid any questionable theory, or to quote as practical results any cases of whose correctness reasonable doubts might be entertained. There are, it is true, some theories propounded, some practices recommended, which are in direct contradiction to those usually received in England. They have not, however, been so advanced, unless the long experience of the most distinguished foreign engineers has warranted him in believing that our own practice is based entirely upon prejudice. We are, whether for good or for evil, essentially a practical nation — we have a dislike to theory, almost to analysis — we examine reluctantly any habit we have long followed. As in politics, so

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PREFACE.

we are even in building. Our forefatners made mortar in one way, as perfect as their knowledge admitted, and doubtlessly that way was all that was practically necessary to secure the results then sought for — so we continue without examination in the track they beat for us. Our requirements are, however, very different. Railroads, and the constructions they necessitate, have modified very materially the science of construction. In England, especially of late years, works have been executed which so immeasurably surpass in boldness anything which had been previously attempted, that we may be justified in expressing our surprise that so few attempts have been made to ascertain the real nature of the materials dealt with. Is it not to this neglect that we may attribute the numerous failures we read of?

Some of these failures have been so remarkable, and some recent business transactions have displayed so singular an inattention to the nature and properties of lime, that the author deems it his right to provoke a discussion upon the subject, trusting that abler heads and hands will complete what he has so imperfectly begun. This branch of chemical knowledge has been so entirely revolutionised ” of late, so much uncertainty still remains to overshadow it, that it would be worse than folly to make any assertion which would lead to a belief that even the very fundamental principles were not, even now, susceptible of modification. That which is to be desired above all things is to rouse the professions of engineers and architects from the apathy with which they treat such subjects as the one before us — the very alpha and omega of their business. There is, however, something so invidious in attacking

PREFACE.

vii

openly a generally received opinion, as the author has done with respect to the mode of making mortar practised in this country, page 66 and subsequently, that he throws himself upon the consideration of his professional brethren, in the hope that they will excuse his boldness on the score of his sincere desire to advance the true interests of science.

At the same time the author would beg to protest very energetically against the rule-of-thumb ” methods which prevail in England in the manipulation of mortars. Architects and engineers, it is true, prescribe certain proportions of lime and sand to be employed ; but in practice the foreman of the pug-mill,” as the labourers call the person entrusted with this work, is the only authority, and he mixes the ingredients precisely as it suits his fancy. In reality, mortar-making is a branch of practical chemistry — on a large scale, it is true — one which does not admit of the care and exactness of the laboratory. But the safety of a building often depends upon the perfection with which this operation is executed, and a certain amount of scientific acquirements is necessary to insure that perfection. For more than twenty-five years the author has been employed in building operations ; but in the whole course of his experience he never saw in any construction, in England, a measure used to ascertain the proportions of the ingredients employed for making mortar.

We have seen of late years far too many accidents happen, too many absurdities committed, not to render it necessary to protest loudly against the carelessness with which the use of limes is regarded. One of the most important works executed of late years in London

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PREFACE.

was built upon concrete made of stone lime, to which iron filings were added at a most tremendous and useless expense. Another large work was described in the specification to be executed with hydraulic lime ; and the engineer allowed common Medway stone lime to be used, although it is very far from being what is properly called an hydraulic lime. We have known viaducts with piers 100 feet high executed with chalk lime ; they have fallen, and been rebuilt with the hydraulic lime which only ought to have been employed ; and we hfear of pozzolana being used still in sea works. Surely, therefore, any examination of the nature of the materials to be used, which will hereafter prevent a repetition of such mistakes, must be of service.

The different scientific associations connected with building would confer a great boon upon the public if they would undertake a series of investigations upon the still undecided questions connected with the chemistry of their respective professions, and also if they would make a statistical statement of our mineral wealth, as far at least as building materials are concerned. We require a series of observations upon the geological and geographical distribution of the rocks able to furnish hydraulic limes. A synopsis of the building stones is also a desideratum ; for the Parliamentary report upon the subject was very far indeed from being a satisfactory solution of its difficulties. Such an inquiry should be undertaken under the auspices of the united bodies of the engineers and architects.

Contents

Chap. Page.

I. Cursory view of the progress of discovery in the science

connected with limes, &c. . . ^ . . . . . 1

Chapter I

CURSORY VIEW OF THE PROGRESS OF DISCOVERY IN THE SCIENCE CONNECTED WITH LIMES, ETC.

The use of some cementing material to bind together the small stones or other materials employed in the construction of walls, and also for the purpose of giving them a smooth surface adapted to receive polychromic or other decoration, dates from a very high antiquity. It is, however, probable that it was subsequently to the discovery of the art of brickmaking, that the ancients arrived at that of burning lime. Indeed, the use of moistened clay, which was found to have a certain ductility, and to harden also in drying, was likely to have preceded that of lime, as a cement; for the qualities and the mode of obtaining the latter were of a nature to require long study and great experience.

The Assyrians and Babylonians appear to have employed either moistened clay, or the bitumen so plentifully supplied by the springs in their country. Some doubt, however, exists as to whether these people did ever really use mortar. Captain Mignan sometimes

B w ON LIMES^ CALCAREOUS CEMENTS,

talks of bricks which were cemented together with a coarse layer of lime. "^At others/^ he says, that '^between the brickwork at irregular distances a layer of white substance is perceptible, varying from ± in. to 1 in. in thickness, not unlike burnt gypsum or the sulphate of lime. From the peculiarly mollified state of the bricks I apprehend this white powder is nothing more than common earth, which has undergone this change by the influence of the air on the clay composing the bricks.^^

The Egyptians, however, used mortar in the construction of their pyramids; and Mr. Cresy has given an analysis of that employed in the construction of the pyramid of Cheops, which shows that they possessed nearly as much practical knowledge of the subject as we do at the present day. [Theory and Practice of Engineering^ pages 717 and 718.)

Sir Gardner Wilkinson also mentions that the inte* riors of some of the pyramids were stuccoed, but he does not give any description by which we might even guess at the nature of the materials employed.

The Greeks, at a very early period of their civilization, used compositions, of which lime was the base, to cover the walls constructed of unburnt bricks. According to Plinius and Vitruvius, the palace of Croesus, the Mausoleum, and the palace of Attains were protected, or ornamented, in this manner. According to Strabo, the walls of Tyre were built of stone set with gypsum, a very common material apparently in Asia Minor, and the centre of the old Assyrian civilization. ^

In Italy the first people who employed mortar in their buildings were the Etruscans. Gori, in his Museum Etruscum^ mentions that in the tombs found near their ancient cities, such as Iguvium, Clusium, Volterra, the constructions were made with mortar. Near Volterra also, in 1739, a cistern, entirely built and lined with that material, was discovered. A branch of this nation, known under the name of Tyrrhenians, w^ere considered by the Greeks to have invented, or at least considerably improved, the art of masonry. The most ancient authors, such as Homer, Hesiod, Herodotus, and Thucydides, speak of them under that name, and call their walls by the word tyrsis,^^ instead of teichos,^^ the one used by the more modern authors. The word ^^tyrsis^^ is supposed to have had the same signification in the Etruscan language ; and the towers erected for the purpose of fortification were also called ^^tyrseis^^ by the Greeks.

The Romans, as is well known, derived all their knowledge of the arts either from the Etruscans or the Greeks. They added little to the general stock of knowledge as to the use of limes, but Vitruvius is the first author upon the subject whose works have descended to us. The text of this remarkable man^s work shows that the ancients, although they adopted a different scientific phraseology from that in fashion in the 18th century, knew as much of the laws regulating this branch of chemistry as the moderns of that time. For all practical purposes Vitruvius is even now as safe a guide as most of the authors who treated the subject subsequently ; at least until we arrive at the researches of M. Vicat. (See Vitruvius^ book ii., ch. 5.)

Plinius and St. Augustin treat occasionally about limes and cements; the former, principally to complain of the malpractices of the builders ; the latter, to seek metaphysical comparisons. On the revival of litera-

B 2 ture, after the Cimmerian darkness of the middle ages, which it is now so much the fashion to admire, the authors who treated upon the art of building, such as " Alberti, Palladio, Barbaro, Philibert de POrme, Scamozzi, Savot, Bullet, and Blondel, did little more than follow in the traces of Vitruvius. There was a difference of opinion, it is true, as to the quality of sand which it was most advisable to use : some new limes, some puzzolanos, terrass, and ashes, were employed to give to certain other limes the faculty of setting under water : but until about the middle of the last century no advance seems to have been made towards ascertaining the principles which regulate this branch of chemistry. '

It is, indeed, worthy of remark, that the more useful arts appear to be carefully studied until the practical results they are capable of producing are ascertained : then the rules drawn from such results are received implicitly for a long period, and any attempt to ascertain the laws which regulate them is regarded as useless. We, the human race, appear to attain empirical knowledge quickly; scientific knowledge arrives at a much later period. So it was with limes : so it is with the casting and puddling of iron — a subject equally, if not more, interesting.

The first serious attempt made to ascertain the causes which gave some limes the power of setting under water, and which modified their rates of hardening, was made by the father of civil engineering in England, John Smeaton, in 1756. Being at that time engaged in the construction of the Eddystone Lighthouse, he found it necessary to have a cement capable of hardening at once in the water ; he therefore began a series of experiments, which are detailed in his account of the building of that work ; book hi., chap. 3. The results he arrived at were very remarkable, not only for their practical utility, but also as an illustration of the ease with which a very acute observer may stop short on this side of the attainment of a great truth. Smeaton found that the commonly received opinion that the hardest stones gave the best limes, was only true as far as regarded each quality considered by itself. That is to say, that of limes not fit to be used as water cements,^^ those made of the hardest stones were the best for certain uses in the air; but that whether obtained from the hardest marble, or the softest chalk, such limes were equally useless when employed under water. He found that all the limes which could set under water were obtained from the calcination of such limestones as contained a large portion of clay in their composition. His experiments led him to use, for the important work of the lighthouse, a cement compounded of blue lias lime from Aberthaw, and of puzzolano brought from Civita Vecchia, near Rome. Even at the present day it would be difficult to employ a better material than this, excepting that the price would ensure a preference to the Roman cement, then unknown. But Smeaton, after giving a table showing that all the water limes were obtained from limestones containing clay in chemical combination, in proportions varying from -fV goes on to say, ^^that it remains a curious question, which I must leave to the learned naturalist and chemist, why an intermediate mixture of clay in the composition of limestone of any kind, either hard or soft, should render it capable of setting in water in a manner no pure lime, I have yet seen, from any kind of stone whatsoever, has been capable of doing. It is easy to add clay in any proportion to a pure lime, but it produces no such effect : it is easy to add brick dust, either finely or coarsely powdered, to such lime in any proportion also; but this seems unattended with any other effect than what arises from other bodies become porous and spongy, and therefore absorbent of water as already hinted, and excepting what may reasonably be attributed to the irony particles that red brick-dust may contain. In short, I have as yet found no treatment of pure calcareous lime that rendered it more fit to set in water than it is by nature, except what is to be derived from the admixture of trass, puzzolano, and some ferruginous substance of a similar nature.”

The stress Smeaton laid upon the presence of the ferruginous substance, led many chemists to attribute the hydraulicity of limes to the presence of the oxide of iron. Guyton de Morveau and Bergmann, finding the oxide of manganese in the hydraulic limes they analyzed, regarded it as producing the effect in question. Their researches were nearly contemporaneous with those of Smeaton. Thirty years afterwards, De Saussure observed that the lime of the Chamouni set under water, though entirely without manganese ; and he, therefore, like Smeaton, attributed this faculty to the presence of clay. In 1813, Colets Descotils, on analyzing the compact marl of Senonches, which yields on calcination a lime capable of setting rapidly under water, found in it nearly one quarter of silex, which led him to the conclusion that the cause of the phenomenon consisted in the presence of a large quantity of siliceous matter, disseminated in very fine particles in the tissue of the stone itself.

To continue the quotation from Vicat : ^^The opinion of Descotils did not weaken or invalidate that of De Saussure, since clay contains generally more silex than alumina; and the two chemists agreed, moreover, in considering the oxide of manganese, if not as a useless element, at least as one which was not essential. This was the state of the question in 1813 ; and it was with the intention of putting an end to all doubts upon the subject that I decided at that epoch to proceed synthetically, and to compose hydraulic limes entirely, by burning different mixtures of common lime, slacked spontaneously, with clay : the success surpassed my hopes. All the clays, rich and soft to the touch, gave the same results ; my experiments were repeated in Paris, iri 1817? with the limes of Cleyes and of Champigny, and the clay from Vauvres ; further experiments, by Mr. St. Leger, in England, and by M. Raucourt de Charleville, in Russia, confirmed the results previously obtained.^^

The subsequent researches of the most eminent chemists and engineers must be considered to have confirmed the theoretical opinion which guided Vicat in his experiments, with a few recent but important rectifications of detail.

Berthier, Dumas, Hassenfraz, Treussart, Thenard, Gay Lussac, Petot, Sganzin, Girard, Parandier, Minard, Kuhlmann, in France — John of Berlin, and Fuchs of Munich — Pasley, Ansted, and Way, in our own country — as well as most of the scientific authors who have treated upon the subject throughout the globe — have arrived at nearly the same conclusions as Vicat with respect to the causes which influence the different actions of lime.

The following condensed statement of the usually j received theory may, therefore, be taken as represent- j ing the actual state of this branch of chemical and ' engineering science.

CHAPTER 11.

CHEMICAL THEORY OF THE ACTION OF LIMES, AND THEIR CLASSIFICATION.

Pure lime, or calcium, as regarded in chemistry, is a metallic oxide, having strong alkaline properties. It is caustic, and turns green the vegetable blues. Its specific gravity, according to Kirwan, is 2*3 ; according to Berzelius, its atomic weight is 20*5 ; according to Dumas, it is 20. It is very difficult of fusion, but greatly assists the fusion of other earthy bodies. At an ordinary temperature, pure water can dissolve of its own weight of lime; but, when boiling, it dissolves less. Dr. Dalton states that water at the following degrees of the centigrade scale will dissolve the following proportions of lime, and of its hydrate ; viz..

At 15° 5 centigrade it dissolves yt2 and -g-iy of the hydrate.

,, 50° 0 „ ,, „

„ 100° 0 ,, „ >»

The pure metallic base never occurs in nature, nor does pure lime, its protoxide. If the pure lime were exposed for a period, however short, it would absorb the water and carbonic acid gas of the atmosphere. We therefore find it in the state of the bi-carbonate.

the carbonate and subcarbonate^ of lime^ in which it is very extensively diffused. The lime of commerce is obtained by the calcination of these carbonates, and the process consists in driving off by heat the carbonic acid gas which is in combination.

The minerals which contain the carbonate of lime, and which are designated under the generic name of limestones,” or calcareous stones,” are of very various natures. They are mostly composed of carbonate of lime, of magnesia, of oxide of iron, of manganese, of silica, and of alumina, combined in variable proportions; and they are also found with a mechanical admixture of clay (either bituminous or not), of quartzose sand, and of numerous other substances. The name of limestone is more especially applied to such of the above mixtures as contain at least one half of their weight of carbonate of lime. . Mineralogists distinguish the subdivisions by the names of the argillaceous, magnesian, sandy, ferruginous, bituminous, fetid,” &c. These subdivisions, again, are often characterized by varieties of form and contexture, which are known specifically under the names of lamellar, sacchroid, granular, compact, oolitic, chalky, pulverulent, pseudomorphic, concreted,” &c., &c.

This nomenclature is important ; for every description of limestone yields a lime of different quality, distinct in colour and weight, in its avidity for water, and especially in the degree of hardness it is capable of assuming when made into mortar. But the physical and mechanical nature of a stone are far from being certain guides as to the quality of the lime it can yield. A chemical analysis of a hand sample also frequently gives different results from those obtained in practice.

B 5

Experience alone should be the final guide of the engineer or of the builder.

The carbonate of lime occurs in nearly all the geological formations, but it is scarce in the primary ones. In the transition rocks it is more abundant; and it constitutes the great mass of the secondary and tertiary ^ formations. It is worked largely, either for the purpose of obtaining building stones, or for burning for lime. The calcareous rocks of the primary formations, and of the early transition series, furnish the greater number of stones which are worked under the name of marbles. The secondarj^- and tertiary calcareous rocks contain the mixtures of clay and other ingredients which render them the most adapted to furnish limes.

After a calcination sufficient to disengage the carbonic acid gas, the limestone will be found to have diminished considerably in weight, and the resulting material possesses the property of absorbing water, either with or without a disengagement of heat. It cracks and falls to pieces whilst thus combining with the water, or slacking, as the workmen call the process of passing into the state of a hydrate of lime.

The principal characteristics of the hydrate of lime are that it is white and pulverulent; much less caustic than quick lime. It parts easily with the first portions of its water of combination if exposed to fire, or even to mere friction ; but it requires a very high degree of heat to cause it to part with the whole of the water. There is still a great degree of uncertainty as to the chemical action of the hydrates. Generally speaking, they are considered not to absorb oxygen; but Treussart supposes that they do so, and that they undergoimportant modifications in consequence. The quantity

MORTARS, STUCCOS, AND CEMENTS. 11

of water that limes solidify in passing to the state of hydrates, is also a question upon which much doubt exists amongst chemists. Berzelius supposed that the hydrates were formed of water and the metallic oxides, in such proportions as that the quantity of oxygen contained in the water should be equal to the oxygen contained in the oxide. Thus, the hydrate of lime absorbs carbonic acid gas from the air, or even (with the best limes) from water, if immersed therein; and after a period, varying with the nature of the limestones from which it is prepared, it solidifies with an imperfect crystallization. Whilst passing into this state, 100 parts of pure lime, which contain 28T6 parts of oxygen, Berzelius supposes to combine with 32T parts of water, which contain also 28‘3 of oxygen. Thenard, however, does not admit this law to hold in all cases ; and certainly some of Treussart’s experiments would induce us to hesitate before we admit it. The hydrates, under the action of the voltaic pile, assume the same action as the oxides. Bodies capable of decomposing water, always acts upon them, even upon such as heat does not affect; acids also decompose the hydrates when these are produced from the oxides of mineral bases.

If, for the purposes of classification, we observe the phenomena which attend the slacking and hardening, or, to use the workman's phrase, the setting of lime, we find that they may be ranged in the following order. The lime in these experiments is supposed to be perfectly fresh, and is to be immersed in a small basket, in perfectly pure water, for the space of five or six seconds only. It is then to be allowed to dry, or at least the loose uncombined water is allowed to run off, and the contents of the basket are then emptied into a stone or iron mortar.

1. The lime hisses, crackles, swells, gives off a large quantity of very hot vapour, and falls into powder instantly : or,

2. The lime remains inert for a period of variable duration, but which does not exceed five or six minutes ; after which the phenomena above described declare themselves energetically : or,

3. The lime, again, remains inert for five or six minutes, or the period of its inactivity may extend to a quarter of an hour. It then begins to give off vapour and to crack, without decrepitating to any great extent. The steam formed is less abundant, and the evolution of heat is less than in the two former cases : or,

4. The phenomena only commence an hour after the immersion of the lime, and sometimes even after a lapse of time still more considerable. The lime cracks, without decrepitation, it gives off little steam or heat : or,

5. The phenomena commence at epochs which are very variable, and in fact hardly perceptible ; the heat given off is only distinguishable by the touch ; the lime does not fall easily into powder, and at times it does not do so at all.

Before the effervescence has entirely disappeared, the slacking of the lime should be completed. As soon as the cracking and falling to pieces begin, water should be poured into the vase, not upon the lime, but by the side, so that it may flow freely to the bottom, from whence it would be absorbed by the portions of the lime in a sufficiently advanced state of chemical action to require it. The compost should be frequently stirred, and sufficient water should be added, taking care not to flood the lime, but merely to bring it to the consistence of a thick paste.

Thus prepared, the lime should be left to itself until all the inert particles have had time to complete their action. The end of this is announced by the cooling of the mass, and it may last from two to three hours, or sometimes even more.

The limes should then be beaten up again, and water added, if necessary, until a paste be obtained as firm as possible, but at the same time preserving a certain degree of ductility. Its consistence should be equal to that of clay ready to be worked into pottery. A vase should then be taken and well filled with this paste ; it should be marked and immersed in water, taking note of the day and hour of the immersion.

Careful observations made upon the limes thus treated show that they may be divided into the five following classes, characterized by the phenomena before described : namely, 1, the rich limes ; 2, the poor limes ; 3, the limes middlingly hydraulic ; 4, the hydraulic limes ; and, 5, the eminently hydraulic limes.

Smeaton and the bulk of the English engineers use the term water lime instead of hydraulic ; but it appeared to me advisable, for the sake of uniformity of nomenclature, to preserve the one adopted throughout the Continent. It is, then, to be understood that wherever the term hydraulic lime occurs, it signifies the same as that of water lime, and means one which possesses the property of setting under water.

1. The rich limes are the purest metallic oxides of calcium we possess, and the purer the carbonate of lime from which they are obtained, the more distinctly marked are the appearances from which they derive their name. These are, that they augment in volume to twice their original bulk, or even more than that, when slacked in the usual manner. If employed by themselves without any admixture of foreign substances, their consistency, even after many years of immersion, is the same as on the first day. If exposed to pure water frequently renewed, the very last particle would be taken up in solution by the water.

2. The poor limes are those which either do not augment in bulk at all, or only do so to a very trifling extent, when slacked. They do not harden under water more than the rich limes, and are acted upon by that agent in the same manner, excepting that they leave a small residuum without consistence.

3. The middlingly hydraulic limes set under water after from fifteen to twenty days’ immersion, and continue to harden for some time afterwards ; but the progress of their hardening diminishes after the sixth or eighth month ; after a year their consistence is equal to that of dry soap. They dissolve, but with difficulty, in frequently renewed pure water. The change of bulk they undergo in slacking is the same as that of the poor limes, but never equal to that of the richer varieties.

4. The hydraulic limes set after from six to eight days’ immersion, and continue to harden ; the progress of this solidification may extend to twelve months, although the greater part of it is completed by the end of the first six. At this last epoch the lime is already of the consistence of the softer building stones, and the water in which it is immersed is no longer able to dissolve even when renewed. Its change in bulk in slacking is about the same as that of the poor limes.