Cottage Building in Cob Pise Chalk and Clay Part 7

_The Value of Ramming._--"Beating, or compression, is used in many different sorts of work; the ancients employed it in making their rough walls; the Italians employ it for the terraces which adorn their houses; the Moors for all their walls; the Spaniards, the French, and others for some of the floors of their apartments. The intent of the ancient architects, when they recommended the beating of cement and other compositions used in building, was to prevent them from shrinking and cracking; and it is employed for the same purpose in walls which are made of earth. The beater, by repeated strokes, forces out from the earth the superfluous water which is contained and closely unites all the particles together, by which means the natural attraction of these particles is made powerful to operate, as it is by other natural causes in the formation of stones. Hence arises the increasing strength and astonis.h.i.+ng durability which houses of this kind are found to possess."

_An Experiment._--"Upon beating a small portion of earth, and weighing it immediately afterwards, it was found to weigh 39 lb. Fifteen days after, it had lost 4 lb. In the s.p.a.ce of another fifteen days it lost but 1 lb.; and in fifteen days after that its weight diminished only lb. In the s.p.a.ce of about forty-five days the moisture was completely evaporated, and its weight was diminished about one-eighth; consequently only one-eighth of the whole ma.s.s was occupied by moisture, and this small proportion cannot at all affect the solidity and consistency of the earth so treated. This experiment is also sufficient to show the difference between this kind of building and that vulgar kind called in England 'mud-walling.'"

_Rate of Work._--"In one single day three courses of about 3 ft. each may be laid one over the other; so that a wall of earth of about 8 or 9 ft., or one story high, may be safely raised in one day. Experience has proved that as soon as the builders have raised their walls to a proper height for flooring, the heaviest beams and rafters may without danger be placed on the walls thus newly made; and that the thickest timber of a roof may be laid on the gables of pise the very instant they are completed."

[Headnote: Suitable Soils]

ON EARTH PROPER FOR BUILDING

_Suitable Soils._--"1st. All earths in general are fit for that use, when they have not the lightness of poor lands nor the stiffness of clay.

"2ndly. All earths fit for vegetation.

"3rdly. Brick-earths; but these, if they are used alone, are apt to crack, owing to the quant.i.ty of moisture which they contain. This, however, does not hinder persons who understand the business from using them to a good purpose.

"4thly. Strong earths, with a mixture of small gravel, which for that reason cannot serve for making either bricks, tiles, or pottery. These gravelly earths are very useful, and the best pise is made of them."

_Soil Tests._--"The following appearances indicate that the earth in which they are found is fit for building: when a pickaxe, spade, or plough brings up large lumps of earth at a time; when arable lands lies in clods or lumps; when field-mice have made themselves subterraneous pa.s.sages in the earth; all these are favourable signs. When the roads of a village, having been worn away by the water continually running through them, are lower than the other lands, and the sides of those roads support themselves almost upright, it is a sure mark that pise may be executed in that village. One may also discover the fitness of the soil by trying to break with one's fingers the little clods of earth in the roads, and finding a difficulty in doing it; or by observing the ruts of the road, in which the cart-wheels make a sort of pise by their pressure; whenever there are deep ruts on a road, one may be sure of finding abundance of proper earth.

"Proper earth is found at the bottom of the slopes of low lands that are cultivated, because every year the rain brings down the fat or good earth. It is frequently found on the banks of the river, but above all, it is found at the foot of hills, and on all cultivated lands which have much slope. In digging trenches and cellars for building, it generally happens that what comes out of them is fit for the purpose."

ON THE MIXTURE OF EARTHS

_Soil Blending._--"As it may sometimes happen that earth of a proper quality is not to be found on the spot where it is intended to build, it becomes of importance to attend to the method of mixing earths; for though the earth which is near at hand may not of itself be proper, it is very probable that it may be rendered so by the mixture of a small quant.i.ty of another earth fetched from a distance. The principle on which a mixture must be made is very simple; strong earths must be tempered with light; those in which clay predominates, with others that are composed more of chalk and sand; and those of a rich, glutinous substance, with others of a poor and barren nature. The degree in which these qualities of the earths prevail must determine the proportions of the mixture; which it is impossible here to point out for every particular case, but which may be learnt by a little practice. Some easy methods will be described, by which any one may make a trial of the qualities of his earth.

"It will not be amiss to mix with the earth some small pebbles, gravel, rubbish of mortar, or in short any small mineral substances; but none of the animal or vegetable kind must be admitted.[5] Such hard substances bind the earth firmly between them, and being pressed and pressing in all directions, contribute very much to the solidity of the whole; so that well-worked earth, in which there is a mixture of gravel, becomes so hard at the end of two years that a chisel must be used to break it, as if it was freestone."

[Footnote 5: "The pise does not admit any vegetable or animal substances. In mud walls they put straw, chopped hay, hair, flocks, wool, etc., to make the mud adhere to the wood, or laths; whereas the workmen who build in pise are careful to pick out the least straw or the smallest bit of root which remains in the earth: in short, the pise is a mineral substance imitating stone, consequently anything that can slake or rot must be excluded."]

[Headnote: Experiments]

EXPERIMENTS TO ASCERTAIN THE QUALITIES OF ANY EARTH

_Trial by Experiment._--"Take a small wooden tub or pail, without a bottom, dig a hole in the ground of a court or garden, and at the bottom of that hole fix a piece of stone, flat and level; place your tub upon the stone, fill around it the earth that has been dug out to make the hole, and ram it well, that the tub may be enclosed, to prevent its bursting. Then ram into the tub the earth you mean to try; putting in, at each time, about the thickness of three or four fingers' breadths: when this is well rammed, add as much more, and ram it in the same manner, and so the third and fourth, etc., till the earth is raised above the brim. This superfluous earth must be sc.r.a.ped off extremely smooth, and rendered as even as the under-part will be, which lies on the stone. Loosen with a spade the earth around the tub, and you will then be able to take it out, and with it the compressed earth that it contains; then turn the tub upside down, and if it is wider at the top than at the bottom, as such vessels usually are, the pise will easily come out, but if it should happen to stick, let it dry in the air about twenty-four hours, and you will then find that the earth is loose enough to fall out of itself. You must be careful to cover this lump of pise with a little board; for though a shower of rain, falling in an oblique direction, will not injure it, yet it may be a little damaged if the rain falls perpendicularly, and especially if it remains upon it. Leave the lump exposed to the air, only covered with a board or flat stone, and if it continues without cracking or crumbling, and increases daily in density and compactness as its natural moisture decreases, you may be sure that the earth is fit for building. But you must remember that it is necessary that the earth employed should be taken from a little below the surface of the ground, in order that it may be neither too dry nor too wet; it must be observed also that if the earth is not well pressed around the outside of the tub before it is filled, though the hoops were of iron, they would burst, so great is the pressure of the beaten earth against the mould, of whatever size it may be."

_The Earth-ball Test--An Experiment which may be made at any time._--"Every person in walking on his ground may make little b.a.l.l.s of earth and press them as tight as he can between his hands. If he brings them home and puts marks on them, he will by that means know the quality of every piece of land, and also be a judge of the mixture it will be necessary to make."

[Headnote: Preparation of the Earth]

ON THE PREPARATION OF THE EARTH FOR BUILDING

_Soil Preparation._--"All the operations of this art are very simple and easy; there is nothing to be done but to dig up the earth with a pickaxe, break the clods with a shovel, so as to divide it well, and then lay it in a heap, which is very necessary, because as the labourers throw it on that heap, the lumps of earth and large stones roll to the bottom, where another man may break them or draw them away with a rake.

I must observe that there should be an interval of about an inch and a quarter between the teeth of the rake, that the stones and pebbles of the size of a walnut, or something more, may escape, and that it may draw off only the largest. If the earth that has been dug has not the proper quality, which is seldom the case, and it is necessary to fetch some better from a distance, then the mixture must be made in this manner: one man must throw one shovelful of the best sort, while the others throw five or six of the inferior sort on the heap, and so more or less according to the proportions which have been previously ascertained."

_Rain._--"No more earth should be prepared than the men can work in one day, or a little more, that they may not be in want; but if rain is expected, you must have at hand either planks, mats, or old cloths to lay over the heap of earth, so that the rain may not wet it; and then as soon as the rain is over, the men may resume their work, which, without this precaution, must be delayed; for it must be remembered that the earth cannot be used when it is either too dry or too wet, and therefore if the rain should wet it after it has been prepared, the men will be obliged to wait till it has recovered its proper consistency--a delay which would be equally disadvantageous to them and their employer. When the earth has been soaked by rain, instead of suffering compression, it becomes mud in the mould; even though it be but a little too moist, it cannot be worked; it swells under the blows of the rammer, and a stroke in one place makes it rise in another. When this is the case, it is better to stop the work, for the men find so much difficulty that it is not worth while to proceed. But there is not the same necessity of discontinuing the work when the earth is too dry, for it is easy to give it the necessary degree of moisture; in such a case it should be sprinkled with a watering-pot, and afterwards well mixed up together; it will then be fit for use."

_Organic Matter._--"It has already been observed that no vegetable substances should be left in the earth; therefore in digging, as well as in laying the earth in a heap, great care must be taken to pick out every bit of root, great and small, all sprigs and herbs, all bits of hay and straw, chips or shavings of woods, and in general everything that can rot or suffer a change in the earth."

ON THE BOND TIMBER TO BE USED IN BUILDINGS OF PISe

_Corners._--"To make good walls, it is not sufficient that the earth be well beaten, we must also learn to unite them well together. Here the binders cost very little; they consist only of thin pieces of wood, a few cramps and nails, and these are sufficient to give the greatest stability to buildings of pise."

Having gone on to explain that the angles of the building are formed by the successive courses alternately crossing one another on the corner like the alternating "long and short" quoins in a stone building, our authority proceeds to describe how rough boards are laid between the courses of pise so as to cross at the corner and so, entirely encased in tightly compressed earth, they form effective ties.

"This board must be rough, as the sawyers have left it, 5 or 6 ft. long, something less than 1 in. thick, and in breadth about 8, 9 or 10 in., so that there may remain on each side 4 or 5 in. of earth, if the wall is 18 in. thick; by this means the board will be entirely concealed in the body of the wall. When thus placed neither the air nor damp can reach it, and of course there is no danger of its rotting. This has been often proved by experience, as in taking down old houses of pise such boards have always been found perfectly sound, and many that had not even lost the colour of new wood. It is easy to conceive how much this board, from the pressure of the work raised above it, will help to bind together the two lengths of wall and to strengthen the angle."

_Bonders._--"It is useful (particularly when the earth is not of a very good quality) to put ends of planks into the pise after it has been rammed about half the height of the mould. These ends of planks should only be 10 or 11 in. long, to leave as before a few inches of earth on each side of the wall, if it is 18 in. thick; they should be laid crosswise (as the plank before mentioned is laid lengthwise) over the whole course, at the distance of about 2 ft. from one another, and will serve to equalise the pressure of the upper parts of the works on the lower course of the pise.

"The boards above mentioned need only be placed at the angles of the exterior wall, and in those parts where the courses of the part.i.tion walls join to those of the exterior wall, the same directions that have here been given for the second course must be observed at each succeeding course, up to the roof. By these means the reader will perceive that an innumerable quant.i.ty of holders or bondings will be formed, which sometimes draw to the right, sometimes to the left of the angles, and which powerfully unite the front walls with those of the part.i.tions; the several parts deriving mutual support from one another, and the whole being rendered compact and solid."

[Headnote: The Strength of Pise]

_Strength._--"Hence these houses, made of earth alone, are able to resist the violence of the highest winds, storms and tempests. The height that is intended to be given to each story being known, boards of 3 or 4 ft. in length should be placed beforehand in the pise, in those places where the beams are to be fixed, and as soon as the mould no longer occupies that place, the beams may be laid on, though the pise be fresh made; little slips of wood, or boards, may be introduced under them, in order to fix them level. The beams thus fixed for each story, the pise may be continued as high as the place on which you intend to erect the roof."

ON THE TIME AND LABOUR NECESSARY IN BUILDING A CERTAIN QUANt.i.tY OF PISe

_Speed of Building._--"Besides the advantages of strength and cheapness, this method of building possesses that of speed in the execution. That the reader may know the time that is required for building a house, or an enclosure, he need only be told that a mason used to the work can, with the help of his labourer, when the earth lies near, build in one day 6 ft. square of the pise."

_Rendering._--"To prepare the walls for plastering, indent them with the point of the hammer, or hatchet, without being afraid of spoiling the surface left by the mould; all those little dents must be made as close as possible to each other, and cut in from top to bottom, so that every hole may have a little rest in the inferior part, which will serve to retain and support the plaster.

"If you happen to lay the plaster over them before the dampness is entirely gone, you must expect that the sweat of the walls will cast off the plaster."

The wall surface having been duly hammer-chipped, the work must be scoured with a stiff brush to remove all loose earth and dust, and to finally prepare it for rough-casting. Rough-cast consists of a small quant.i.ty of mortar, diluted with water in a tub, to which a trowel of pure lime is added, so as to make it about the thickness of cream.

One workman and his labourers are sufficient; the workman on the scaffold sprinkles with a brush the wall he has indented, swept, and prepared; after that he dips another brush, made of bits of reed, box, etc., into the tub which contains the rough-cast, and throws with this brush the rough-cast against the wall.

"Rough-cast, which is attended with so little trouble and expense, is notwithstanding the best cover that can be made for pise walls, and for all other constructions; it contributes to preserve the buildings. It is the peculiar advantage of these buildings that all the materials they require are cheap, and all the workmans.h.i.+p simple and easy."

_Local Testimony._--At the end of the article just summarised, an instructive letter from a former rector of St. John's, La Roch.e.l.le, is quoted:

"SIR,--

"My having been an inhabitant for some time of the town of Montbrison, capital of the Forets, enables me to give you some information concerning the mode of building houses with earth, etc.

[Headnote: A Pise Church]

_A Pise Church._--"The church was the most remarkable in this style of building; it is about 80 ft. long, 40 ft. broad, and 50 ft. high; the walls built in pise, 18 in. thick, and crepe, or rough-cast on the outside, with lime and sand. Soon after my arrival, the church, by some accident, was destroyed by fire, and remained unroofed for about a twelvemonth, exposed to rains and frost. As it was suspected that the walls had sustained much damage, either by fire or the inclemency of the season, and might fall down, it was determined to throw them down partially, and leave only the lower parts standing; but even this was not done without much difficulty, such was the firmness and hardness these walls had acquired, the church having stood above eighty years; and all the repairs required were only to give it on the outside, every twelve or fifteen years, a new coating of rough-cast.

"A house for a single family is generally finished in about a fortnight.

The following is the method I have seen them practise."

_Building Procedure._--"The earth is pounded as much as possible, in order to crumble any stones therein; clay is added thereto in a small quant.i.ty, about one-eighth part. It is all beaten and mixed up together by repeated blows with a mallet about 10 in. broad, and 10 or 15 in.

long, and 2 in. thick. The earth being thus prepared, and slightly wetted, the foundation of the house is dug for; this is laid with stone, and when it is about 1 ft. high above the surface of the ground, planks are arranged on each side, which are filled with earth intended for the wall; this is called Pise in the dialect of the country. It is strongly beaten; and this method is continued successively all round the building. The walls have more or less thickness according to the fancy of the owner; I have seen them 6 in. and 18 in. thick. If several stories are intended in such erections, they do not fail to place beams to support the floors before they build higher. Of such buildings I never saw any consisting of more than three floors at most; generally they have but two. When the building is thus finished, it is left for some months to dry; then such as wish to make the building more solid and durable, give it a rough-cast coating on the outside with lime and sand. This is what I have observed during a residence of three years in the town of Montbrison. I should be happy if this detail should afford the slightest information to the generous nation which has received us with so much goodness.