Concrete : its use in building and the construction of concrete walls, floors, etc.

Preface

This small work is intended to deal in a practical manner with the treatment of a material that has yet undoubtedly to come into more general use. No attempt has been made to give the “ reason why ” in many cases the behaviour of concrete stands so pre¬ eminently above all other materials for special pur¬ poses, nor to explain the theory of cement setting, and the chemical process developed in the operation of making concrete ; these subjects have already found more capable exponents; but simply to give an unprejudiced statement of the various forms in which concrete can be applied, and most suitable purposes oi which h is adapted. Also to reconcile those extremes of individual opinion engendered on the one hand by inability to see that concrete possesses any defects, and on the other by that veneration for existing forms and processes of building, that creates a burst of indignant feeling when innovation of any kind is even suggested.

Statements herein made as facts are the result of personal observation and experience, except where the authorship is acknowledged, and are based upon long practice under variable conditions.

The Importance of Proper Specifications for Concrete Buildings. 168

Index

A.

Page

Accident to a concrete building on Metropolitan Bailway. 41

Adie’s cement-testing machine . 61

Advantages and disadvantages of concrete roofs. 133

Aesthetics of concrete . 5

„ burnt clay, 37; chalk, 38; coke, 37; flints, 34;

mill cinders, 37 ; old stones, bricks, &c., 33; pea gravel, 33 ; pit gravel, 36 ; pottery and brick yard debris, 35 ; river gravel, 35; sea beach, 36;

slag, 32; Thames ballast . 34

„ proportion of smaller materials in . 13

„ error in selecting . 41

,, experiments with various kinds of . 52—54

„ materials suitable for . 32—39

,, necessity for clean. 42

,, suitable for fire-proof construction . 117

„ size of . 33

„ shape of . 33

,, washing of impure. 34

Air slaking ordinary lime. 73

Alberti on concrete . 10

Amalgamation of materials, necessity for proper . 30, 31

Amount of water necessary for making concrete . 82, 153

Appliances for forming monolithic structures. 84—97

B.

Beton, buildings executed by M. Coignet with Blake’s stone crusher .

Index.

viii

Page

Block building with concrete . 24

Blue lias lime as a matrix . 72—74

Board of Works and the Building Act . 21

Bonding concrete and the Metropolitan Board of Works . 21

Brannon’s patent floors, ceilings, &c. 105

Brickwork v. concrete . 55

Bridge built with concrete . 18, 19

Brighton concrete sea-wall . 15

Broomhall Company’s patent facing blocks . 26

Broughton’s patent appliances. 95

Builder, Building News, and Field on concrete. 17

Building-in window and door frames . 142

Building News— prize for a concrete villa. 166

C.

Casting pier caps, sinks, water-troughs, copings, &c. 144

Causes for concrete not being more generally adopted . 7—9

Chalk as an aggregate . 38

Change of form a disadvantage of concrete. 125—128

Chilton Candover farm buildings . 161

Clean aggregate a necessity for good concrete. 42

Cob and mud walls. 13

Coignet, M., and “ beton agglomeres ” . 16

Comparison of cost—concrete v. bricks. 155, 156

„ ,, concrete v. stone. 158—160

Concrete, Alberti on .... 10

,, accident to buildings erected with . 41

,, buildings, necessity for correct plans of . 134

,, building, workmen most suitable for . 135, 136

„ bridge on the Metropolitan Railway . 18, 19

,, block building with. 24

„ block building and Mr. Reid, C.E. 25

„ blocks, Sellar's patent . 27, 28

„ blocks, Broomhall Company’s . 26

„ v. brickwork, comparison of strength . 55

,, building appliances . 84—97

,, buildings erected by Mr. Ranger . 16

„ disadvantages of block building with. 24—28

„ disadvantages of... 93, 94

Index.

IX

Concrete,

99 9 9 99 99 99

experiments with various kinds of.

exaggerated description of the properties of _

foundations for bridge over the Liffey.

floors without iron supports .

floors j. .

French system of forming floors of.

frames, time necessary to remain fixed .

failure of floor made with.

house near Gloucester .

how to make .

houses, and the late Emperor of the French .

lighthouse at Jersey ...

mixing machines.

materials employed in making .

muddy water fatal to sound.

necessity of care in building with .

not a modern invention .

prejudice against .

Palladio and.

public misstatements relative to .

roofs.

reasons for not coming into more general use of

river walling at Chatham and Woolwich.

slabs, Lascelle’s patent.

slates unsuitable for use in.

stairs .

is subject to expansion and contraction.

sea-walls at Bighton .

Semple and .

the Land Improvement Commissioners and .

the Builder, Building News, &c., on.

the Metropolitan Board of Works and.

walls, ventilatmg flues in .

walls, packing of.

walls, and “ broken bond”.

,, walls, result of moving appliances too quickly

,, walls of Reading Abbey.

„ walls of Corfe Caste.....

Cost of water tanks .

„ concrete in farm buildings .

Page

. 38

.. 53—55

. 9

. 11

. 115

.102—124

. 116

. 136

123, 124

. 16

.. 74—83

. 85

. 19

98—101

. 23

. 10

. 8

131—134

. 8, 9

. 15

... 28, 29

. 35

. 151

125—128

. 15

. 11

. 17

. 17

. 21

. 142

. 137

. 143

. 136

. 11

. 11

. 150

. 162

X

Index.

Page

„ fixing concrete appliances . 155

,, iron and concrete floors . 109

„ blue lias lime. 73

„ selenitic cement . 71

„ Blake’s stone crusher . 33

D.

Dennett’s patent material for floors and ceilings. 103, 104

Diminution in bulk of concreted materials. 154

Disadvantages of concrete appliances . 93

„ concrete for building purposes .125—130

„ concrete block building. 25, 26

Drake’s patent concrete appliances . 88—90

E.

Error in selecting aggregates. 41

Experiment with chalk concrete . 38

„ in building cottages. 158,160

,, with concrete floor . 107, 115—116

External treatment of concrete walls, &c. 163—167

E.

Farm buildings and cottages . 160

Fire-proof construction, aggregates suitable for . 117

„ Dennett’s material for . 118, 119

Floors for basements, cellars, &c. 118

Floor construction . 102—124

Floors of concrete, experiment with. 102, 107

„ Frost’s patent . 103

„ Turner’s patent . 104

,, Dennett’s patent . 103, 104

„ Brannon’s patent... : . 105

„ and iron joists. 107—114

Index.

xi

Page

Floors of concrete, experiment with .107, 115

„ cost of . 109

„ methods of finishing . 109_ 112

„ relative cost of wood floors and. 109, 111

„ French system of making . 116

„ failure of . 123, 124

Flat concrete roofs . 131 , 133

Flint facing to concrete walls .. 164

Flues, construction of . 139

Foundations, good materials necessary for. 41

Frost’s patent floors and ceilings. 103

G.

Garden paths. 146

Granite Breccia. 17

Grant, Mr., on the comparative strength of fioman and Portland

cements .. 44

„ experiments with Portland cement, by. 51—64

„ on the strength of vatious aggregates. 52

,, on the fitness of sands for mixing with cement... 56, 57

,, and selenitic cement . 70

H.

Half-timbered buildings . 166, 167

Hastings Cottage Improvement Society and cost of concrete

walls. 157

Homersham, Mr., on the cost of concrete walls . 157

Horticultural purposes, concrete for . 145

House built with concrete near Gloucester . 16

How to make concrete .75—83

I. Incombustible and fire-proof floors.114_117

Introduction ..... 1 21

Invention of conci’ete building appliances...,. 21

Index.

xii

Page

Iron and concrete floors .107—114

Iron hoop as bond for walls . 127

Iron joists stronger when embedded in concrete . 112

L.

Land Improvement Commissioners and concrete. 17

Lascelles’ concrete slab buildings .29, 29

Lime concrete more impermeable to sound than cemeot concrete 130

Lighthouse built of concrete ... 19

Lintols not required in concrete walls . 140

Lish’s patent concrete appliances .92, 93

Lord Kinnaird’s buildings in Perthshire. 157 — 159

M.

Macleod’s concrete-building appliances . 85

Materials suitable for aggregates. 23

Matrices ...43, 64

„ Roman cement .43, 44

,, origin of the term . 43

Parker’s cement . 44

„ Medina cement. 45

,, Poitland cement .45, 64

„ Scott’s cement . 65

,, Selenitic cement .66—72

„ lias lime.72—74

Measuring boxes.78—81

Medina cement . 45

Metal gutters and concrete roofs. 132

Method of making concrete.%.,...81—83

„ finishing surfaces of concrete floors.109—112

„ forming temporary supports for concrete floors... 119, 120

„ finishing under tides of floors and ceilings.120, 121

Messent’s concrete miser. 98

Michele’s cement-testing machine . 63

Mixing boards .34,76, 77

Index, xiii

N.

Page

Necessity of proper care in erecting concrete buildings.30, 31

„ correct plans of concrete buildings . 134

„ for cleaning concrete appliances . 138

Objections to the block system of building . 28

Osborne’s patent concrete building appliances .87, 88

P.

Packing concrete arches and floors . 122, 123

,, concrete walls . 137—154

Palladio on concrete . 10

Parker’s cement. 44

Patented appliances for monolithic construction. 84—97

Paths . 14G

Pebble facing to concrete walls . 165

Permeability to sound of concrete . 129

Pipes encased in concrete walls . 142, 143

„ when invented . 45

„ adulteration of . 30

„ not properly understood. 45

„ and Mr. John Grant, C.E. 45

,, specification of. 46, 47

„ Board of Works test for . 46

„ original specification of patent for . 46, 47

„ present method of manufacturing . 47, 48

„ weight of . 49

„ advantages of . 50

„ experiments on the strength of. 51

,, most suitable aggregate for using with. 52

,, experiments with, and with various kinds of sand 57

,, method for testing the quality of. 59—64

„ machines for testing . 61—64

XIV

Index.

Page

Porous aggregates . 83

Potter’s patent concrete appliances . 90—92

Precautions necessary in mixing concrete. 82

,> „ with temporary timber supports. 126

„ „ when walls dry too quickly . 128

,, „ with holes and cavities in concretewalls 139, 140

Prejudice against concrete . 6, 17, 18

Proportion of fine and coarse materials in concrete. 40

Purposes for which concrete is best adapted. 161

Q.

Qualifications necessary for concrete appliances. 95—97

E.

Reading Abbey concrete walls. 11

Eeid, Mr., on concrete block building. 25

„ and the origin of the term “ matrix ” . 43

Relative cost of concrete and wood floors . 110, 111

Rennie, Mr. George, and concrete for breakwaters . 14

Result of removing concrete frames too quickly . 136

Ridley’s concrete mixer. 99

River walling at Chatham and Woolwich . 15

Road gutters . 145

Roman cement as a matrix . 43, 44

,, the invention of . 44

Roofs of concrete .131—133

„ houses on the Redcliffb Sstate at Kensington . 132

Rough cast on concrete walls ... . 165

S.

Band most fitting for mixing with cement. 57

Scaffolds for concrete buildings . 140, 141

Scott’s cement . 65

Scott Burn, Mr., and concrete appliances . 84

Sgraffito panels for concrete walls . 164

Sea walls built with concrete . 15

„ water and Portland cement . 50

Index.

xv

Page

Selenitic cement . 66—72

„ and common limes as matrices. 65—74

„ instructions for using . 67

„ meaning of term .,,. 66,67

„ table of strength of... 69

„ cost of . 71

Sellar’s patent concrete blooks. 27, 28

Semple, and the construction of bridge over the Liffey . 11

Shams ia building. 6

Shape of aggregates . 33, 40

Shrinkage of concrete . 154

Size of aggregate . 33

„ test sieves for cement. 49

Slab concrete floors . 107

“ Slaking ” ordinary lime. 72

Slates unsuitable in concrete . 35

Smoke flues, construction of... . 139

Specification for a concrete building . 168—175

Stairs of ooncrete . 151

Stamped patterns for concrete walls ... . 165

Stoney’s concrete-mixer . 99, 100

T.

Table of strength of Portland cement neat . 51

„ „ „ „ and sand . 52

„ „ different descriptions of aggregates . 53

„ „ concrete v. brickwork, and neat Portland

cement. 55

„ „ cement with various sands . 57

„ „ selenitic cement . 69

Tail’s patent concrete appliances. 20, 85—87

Tanks . 149

„ patented appliances for constructing. 92

Testing machines . 61—64

Time necessary for concrete frames or moulds to remain fixed ... 137

To prevent sound passing through concrete walls . 130

Treatment of chalk for concrete . 39

Turner’s patent fire-proof floors and roofs. 104

Tyerman’s iron hoops for binding walls. 127

XVI

Index.

V.

Page

Value of hire, or use and depreciation of concrete appliances ... 155 Ventilating flues in concrete walls . 142

W.

Wonnacott, Mr., and the cost of concrete building. lo7

Washing impure aggregates. 34

Water channels, &c. in concrete walls . 142, 143

„ tanks . 149

„ required for mixing concrete, amount of . 153

Weight of concrete appliances. 96

Wilkinson’s concrete stable paving. 30

Wood and concrete floors combined . 103

,, paving to concrete floors . m> H2

„ blocks for fixing joinery thereto in concrete walls. 141

Workmen most suitable for concrete building . 135,136

CONCRETE:

ITS USE IN BUILDING, AND FOR OTHER PURPOSES.

Introduction

When we reflect, that the inhabitants of civilised countries pass, on an average, more than a third, perhaps nearer one half, a lifetime within the walls of their dwellings, or of other buildings, it is something marvellous what apathy, as a rule, is shown to their healthfulness. In no other instance probably is the old adage, “ Out of sight out of mind,” of such universal application, as in the utter disregard paid by so many to the ordinary wholesome construction and main¬ tenance of the houses they live in. If sinks have the indispensable “traps,” it is considered of little importance to ascertain whether they are really what they profess to be, or, as in many known cases they have proved to be, “ fever and death traps.” Provided there are drains supposed to convey away the sewage,, it is assumed there is no need to inquire if they are sound, whether they lead through portions of build¬ ings that should by all means be avoided, or if it were not possible to keep them outside altogether, and whether or not they discharge into cesspools hermeti¬ cally sealed and never emptied. With the “ acme of

B

Introduction.

modern civilisation,” a water-closet, it is qnite possible the foul gases engendered therein have no means of escape, other than through an inefficient water trap, direct into rooms perhaps occupied as sleeping apart¬ ments, or the water for domestic use is obtained from the same cistern which supplies the water-closet, and the cistern itself has perhaps not been cleansed within the memory of anyone who could possibly answer that question. So that the floors of rooms, a few inches removed from the natural soil, or their sleeper timbers partially buried therein (not at all an unlikely occur¬ rence with cheaply-built cottages and villas), are planed to look smooth and clean, it is most unusual to remove a board and look beneath, although probably some curiosities of vegetation and specimens of fungi, emitting most unwholesome smells, would be disco¬ vered, and the space between the floor and the earth found to be deficient of the slightest ventilation.

But if a house has a showy portico, with a flight of stone steps leading thereto, or some other form of attraction, it will—with by far the greater number— atone for a multitude of shortcomings in other respects ; and if moreover the walls are brick-built, the bricks coloured to make them look uniform and hide their defects, and the joints “ tuck pointed,” scarcely one person in a thousand would consider for one moment, whether or not they would absorb an indefinite amount of rain, and what must become of all the moisture they imbibe. If the walls will just, and but just, keep the wet from penetrating as far as the paper-hangings, the house is declared to be per¬ fectly dry, and no thought is given as to the mass of damp material encompassing the inmates on all sides,

I

Introduction. 3

and explaining the chilly feeling experienced, except in hot weather, on entering a room where there is no fire; should rain, however, find its way completely through walls, plastering, and paper, it is assumed, if proposed to make a perfect cure, that the proper thing to do is to batten the walls, and then lath-and-plaster them, leaving an uninterrupted run for rats and mice, who, if they find no other means of entry, will consider it hut little trouble to eat their way through the brickwork itself; hut if battening and plastering is too costly, the more economic method of battening, canvassing, and papering is resorted to. In either case the inmates are little better off than if wrapped in a thick wet blanket, but so that the evil cannot be seen its existence is ignored. If, however, houses are inhabited, or other reasons prevail, then the brickwork is treated externally with some pro¬ fessed water-proofing material—as “Gay’s solution,” “ Szerelmey’s liquid,” “petrifying silicate,” and many others, the manufacture of which —specially to cure damp walls — finds employment for no inconsiderable number of workmen. Correspond¬ ents of technical journals are constantly seeking advice for the same evil, and are recommended gas tar, soap made into a solution with water, a covering of cement or roofing slates, and other specifics.

The universal love for bricks and mortar, with all their shortcomings and failures, will not probably for some time to come be supplanted to any very great extent by the introduction of any new, or the reintroduction of any old and abandoned material for wall building, no matter how strong, weather-proof,

b 2

Introduction.

durable, or economical it may be. Of late years there have been many substitutes invented, as Ransome’s silicious stone, terra-cotta, and Taylor’s [facing bricks, all which, though equal in appearance and far superior to common bricks in durability and impermeability, can never be employed but to a limited extent, owing in a great measure to their cost, especially in remote districts, where the carriage would form a heavy item. On the other hand, the scarcity of good bricks, and the fact that they are only to be had at an extravagant cost—if quality is a consideration—the high price of labour, and the possibility that any building may experience a rest during construction, should a terra-cotta keystone or ornament happen to be fixed by any one but a recog¬ nised bricklayer, must eventually create a wide-spread feeling that the really most important portion of buildings—the walls—must in many instances be formed of something besides bricks, and the workman¬ ship be capable of execution by others besides brick¬ layers. A material which should be as economical in any neighbourhood as bricks and mortar, should com¬ bine strength with durability, be proof against rains and frosts, withstand the injurious action of smoke, and be easy of application by unskilled labour, has, till within the last few years, been an acknowledged want, and that want, it is improbable, will be nearer realised for some time to come by anything but con¬ crete. That Portland cement and lime concretes must and will, however, come into general use for building purposes eventually, does not admit of a doubt; at the same time local circumstances, with regard to natural productions, and the character and purposes of in-

Introduction.

tended buildings, must still be the means in a large measure of deciding as to what shall be used in construction; and when the prejudice against concrete, like other prejudices, has died out, it will take its proper position as a valuable and, in most cases, an economical material—not to supersede everything else, but as a useful adjunct in building.

It is well worthy of notice, that of late the opposi¬ tion to the use of concrete has resolved itself almost entirely into the question of “ ^Esthetics.” The doubts about strength, durability, and other essential quali¬ ties, have given way to nearly the only remaining important difficulty, viz. how to treat it in such way that shall be reasonable and consistent, without imi¬ tating any other material, and without pretence of being something totally different from what it really is. Unfortunately for the reputation of Portland cement, it has clothed so many dilapidated and rot¬ ten structures, that the very name of stucco, with many, savours of a sham, and no other building material has probably been so well abused and less deserving it. For Portland cement has no rival, save such costly articles as granite and some other natural stones, for defying atmospheric changes, frost, rain, or the chemical action of smoke in large towns. There is nothing can be so easily and economically moulded into any shape or form for architectural purposes without distortion, and that will bear ex¬ posure to the vicissitudes of our own or any other climate; and there is no other material that can be applied to so many various requirements in building with such satisfactory results. The facing of concrete walls with Portland cement, only because it has been

Introduction.

found impracticable as yet to build them with sufficient truth and regularity, and with even surfaces, so as to require no further application afterwards of any finer ingredients of the same nature, is in itself not so much a sham as are the fronts of one half the houses erected. Brickwork, more often than otherwise, is stained to make it of an uniform colour, the joints pointed with quite a different and superior mortar to that used in construction, and the outside portion of the walls built with bricks of a much better quality than the inside. Terra-cotta in walls is scarcely ever more than a few inches in thickness, nor would any advantage accrue w r ere it possible and usual to have it the full wall thickness. Stone fronts of many mansions and other costly, buildings are merely veneers of stone, backed with common bricks. Where scagliola for wall-surface decorations, columns, and pilasters; enamelled slate for chimney-pieces and other fittings—both are openly recognised as imitations of various marbles; parquetry made to represent costly oak wainscoting, (the oak being the thickness of a wafer !) deal is stained to represent oak ; fittings and furniture are made of fir and veneered with the most costly woods; plaster and other orna¬ ments are clothed in gilt and lacquer—where all these and many more shams abound, with many, con¬ crete would not be admitted, if, for appearance sake, it had to be covered with a finer quality of the same kind of materials of which it was composed, and of which it would form an integral part. Possibly there will be nothing invented or introduced as a finish for concrete walls externally, that will require eventually less maintenance, cost less in execution,

Introduction.

and defy climatic changes so well, as a coating or covering of Portland cement and sand, and in favour of this method the remark made by Mr. Eeed, M.P., relative to the ugliness of iron-clad ships will well apply—“ The beauty of a thing consists of its com¬ plete adaptation for the ultimate purpose in view and surely the ultimate purpose of a house is to give its inmates the healthy shelter necessary for long life and its enjoyments.

But although the irrepressible cement stucco may be, for the reasons stated, a suitable way of finishing concrete buildings, it does not follow tha fno other method is open, the fact being that there is nothing so susceptible of different methods of treatment, or that affords an ingenious mind so wide a field for artistic effect and constructional development, as concrete. It is a significant fact that, although there have been, comparatively speaking, no end of inventions for making brick buildings damp-proof, nothing has as yet been offered in any shape for the purpose of rendering the same service to concrete walls (evidence in itself that the material requires no such extraneous aid), or as a remedy for incipient decay, a disease which attacks not a few stone build¬ ings. The adoption of concrete so sparingly for constructional purposes, although it has been before the public for some years, may be however accounted for in various ways, besides the hereditary fondness for bricks and mortar, and the apathy displayed by so many as to the nature of the wall materials of houses, from a sanitary point of view; vested interest in brick-making, lime-burning, or bricklaying, and the policy of investing in concrete building appliances as

Introduction.

part and parcel of the ordinary plant of a builder, have all had their share in the general result. Not the least, however, of the causes, has been the ex¬ aggerated statements put forth by patentees, whose sole interest has been to sell concrete machinery and create royalties, and which statements have caused disappointment to those who, without any previous knowledge of the subject (or perhaps of building in any form whatever), have been led to believe that the use of concrete will effect a saving of 50 per cent, in the cost of construction, and who have failed to foresee that the materials of which the walls are built can have but little influence on the value of the carpentry, the painting, the slating, &c. As the cost of the walls would he in an ordinary way perhaps one-third of that of the whole building, the saving of one-half their cost, which it is fair to assume might under special circumstances be the case, would entail a diminution of one-sixth only of the total outlay. In another way, giving the cost of a cubic yard of concrete, which it would seem was apparently a matter not easy to get far wrong in, when the market value of the materials are stated, and the propor¬ tions in which they should be used, the writer of the statement and a well-known concrete builder made it appear that the actual outlay would be 25 per cent, below what it should have been, through calculating sixteen bushels to a cubic yard ; and, most remarkable of all, this statement not only remained undisputed, but was copied into a well-known builders’ price book.* It is to be hoped, in the builders’ interest,

* Atclileys, 1808 .

Introduction.

no very heavy contracts for concrete buildings were undertaken from estimates framed on this hypothesis. And the exaggerated statements as to strength and capabilities have only tended to make the uninitiated portion of the public disbelieve anything and every¬ thing connected with it, for concrete has been pro¬ claimed a “salve for every sore,” a “panacea for every evil,” where a building was concerned. It has been stated over and over again to be ten times stronger than brickwork, which taken in a certain sense might be true ; but, as read by anyone un¬ acquainted with the subject, would be understood to mean that a concrete wall six inches thick was equal in strength to a brick wall five feet thick,— a comparison that has no semblance of reason in it. And, again, why concrete has found but little favour with many, is because it is assumed to be an untried material which age may deteriorate; but this is an assumption that will not bear reflection, for, whether formed with lime or cement, concrete is really a random rubble wall of cement or limemortar as the case may be, and in the construction of which the materials are blended together, and interlocked one with another, in a way that could not possibly be attained by the ordinary method of forming that class of work, and with the additional advantage that the cementitious ingredients must for obvious reasons be of the best and purest descrip¬ tion, not composed of street scrapings, or garden soil, mixed with a modicum of lime, and with which a large proportion of the walls of brick buildings forming suburban London and many other places are built (and plastered as well—fortunately the ac-

Introduction.

tion of the lime destroys in a measure the foetid matter contained therein). Let an unprincipled builder be ever so crafty, he cannot well build the inside of his concrete walls of a different material to the outside—cannot so easily face them with some¬ thing fairly substantial, and leave the back a mass of rottenness—a well-known and every day occurrence with brick, rubble, or flint walls, where efficient super¬ vision cannot be practised, or where houses are built to sell for the highest sum they will realise.

With regard to being a modern invention, history repeats itself in this as in most other things, for the Greeks and Romans undoubtedly used it, and it exists now in the foundations of many of their ancient build¬ ings.

Palladio says : “ Coffer work was made by taking

boards laid edgeways, according to the thickness of the walls, filling the void or space between them with cement and all sorts of small stones mingled together, and continued after this manner from course to course and Alberti also writes: “I have observed that in other places the ancients, who were wonderfully expert in making great works, followed different methods in filling up the foundations. In the sepul¬ chre of Saint Antonini they filled them up with little pieces of very hard stones, each not bigger than a handful, over which they perfectly drowned the mortar. I have known other instances where the ancients have much the same sorts of foundations and structures too —of coarse gravel and common stones that they have picked by chance, and which lasted many ages.” Here there is a positive assertion that concrete, not only for foundations but for the walls themselves, must