Cottage Building in Cob Pise Chalk and Clay Part 12

PISe, PRACTICE AND PLANT

Now that so many able architects and enterprising bodies are seriously taking up pise-building, the improvement in plant and technique should be both rapid and considerable. The School of Pise Building established at Hornchurch in Ess.e.x, by the Imperial Ex-service a.s.sociation, should alone provide us with much new and valuable knowledge of a highly practical kind.

It is there, for instance, that various types of shuttering and rammers are being experimentally tested side by side, and their relative efficiency under varying conditions ascertained. Under some conditions it is probable that the floor and roof timbers (destined for use in the house under construction) will be found the most economical and satisfactory form of temporary "shuttering" for the making of the earth walls.

The pise "Test-House," built by Messrs. Alban Richards at their Ashstead works, was built in this way, and proved highly satisfactory.

Another effective and more generally applicable form of shuttering (designed and manufactured by the same firm) is ill.u.s.trated in the diagram reproduced below. It should be observed that wedges intervene between the movable shutters and the uprights.

The method of employment of the "Mark V" shuttering is well ill.u.s.trated by the bird's-eye view showing the Newlands cottage under construction.

[Headnote: Alternative Shutterings]

In this matter of shuttering there is still, however, great scope for improvement, and it may be hoped that soon ingenuity and experience will jointly produce a complete pise plant perfectly fulfilling all the many conditions enumerated earlier in the book.

Shuttering made by riveting plain galvanised sheet iron to one side of a corrugated sheet has the qualities of lightness, smoothness, cheapness, and rigidity, and the claims of the inventor and patentee are now being put to the test in actual building.

[Ill.u.s.tration: PATENT SHUTTERING FOR PISe DE TERRE _By W. Alban Richards and Co._]

There now seems little doubt but that pise blocks will be largely used for part.i.tions and chimney stacks where the soil is good enough, and experiments are being made with a view to discovering the best and cheapest way of making earth slabs similar to those of c.o.ke-breeze and concrete.

The size aimed at is 18 in. by 18 in. by 3 in., the edges to be tongued and grooved.

Certain "concrete" machines seem to lend themselves to adaptation for the making of earth blocks, but it is necessary to remember that sharp blows are required rather than a steady pressure, and also that we are working with a _dry_ material. The ordinary primitive way of making pise blocks is indicated below.

The hand-rammers are undoubtedly worth study and careful design. A set of three seems to meet all ordinary requirements, and those shown on p.

101 may be taken as typical. They should be of hard-wood, smoothly finished, and provided with long handles. They should be 9 in. to 12 in.

long, and about 5 in. by 4 in. at maximum cross section.

In the sketch they are shown "narrow-ways-on." No. 1 is used for preliminary pounding and final finishing, No. 2 for general consolidating, and No. 3 for working along the edges, against window stops, and under cross-ties.

A South African correspondent, Major Baylay, makes interesting comment as regards rammers and local pise practice:

[Headnote: South Africa]

"My experience of all black labour is, that they won't put any 'guts'

into it. They therefore want fairly heavy rammers, which they can lift and drop, say a foot, and which will do the rest for them. The heat of the sun and extreme dryness of atmosphere out here make it advisable to cover up completed courses at once with sacking, moist for choice, otherwise it is liable to dry out too quickly and crack. It dries out uncovered at night very well, when there is no rain.

"The red loams of South Africa, where not too sandy, make excellent pise. They or their equivalent are found almost everywhere. In the dry state they set so hard that moisture added just before ramming is useless. A large heap must be made, well damped and covered over with moist sacking, and left until the moisture is distributed throughout the ma.s.s. When about four or five days old, in ordinary weather, the earth is ready to use--viz., just wet enough to bind when gripped in the hand.

It should be pa.s.sed through a sieve. I use a sort of 'chicken run,'

8 ft. long, and throw the earth on to it before using. Six feet of it is -in. mesh, and 2 ft. -in. mesh; the reason for this is that, if the earth is a little too dry, it does not always bind well with the previous layer. Therefore, put a few petrol tins of the fine earth into the shuttering first in order to ensure good bond, and throw the coa.r.s.er stuff in after."

[Ill.u.s.tration: PISe HAND RAMMERS]

_Second Note by Major Baylay, Peter Maritzburg, Natal, South Africa_

"I have completed a small building, and though weather conditions have been as bad as possible, it is sound and very satisfactory.

"In my opinion, pise-building should not be attempted in the rainy season in Africa. Earth contains too much moisture, and the power of the sun dries it out too quickly and causes cracks.

"_Re_ plastering. I covered the outside and inside with a mixture of 6 earth, 2 sand, 1 blue (Hyd.) lime, the earth being the red, rather 'fat'

earth found everywhere, and the same stuff the house is built of. It is put on thin with a trowel, after damping the wall. When it dries and cracks, rub all over with a sacking pad covered with the plaster mixture, but wetted to a thin cream consistency. It may sound an odd method, but the natives do this work well, and the result is as good as one can wish for. You can put tar or any wash (No. 6) on this."

[Headnote: Soils]

SOILS

Were it not for the fact (often somewhat embarra.s.sing) that soil quite incapable of making good pise will none the less produce enthusiastic pise-builders, a warning as to the vital importance of the earth being really suitable might seem superfluous.

The author has found some of the staunchest champions of pise-building living on and valiantly struggling with stiff glutinous clay and almost pure sand.

Even the most vigorous optimism can achieve little under such adverse conditions unless soil-blending be resorted to, and even so, pise-building begins to lose points in the matter of economy directly complications of this sort are introduced.

Fortunately, however, England is well off in the matter of pise soils, the red marls being amongst the very best.

A study of the country, or, failing that, of the geological maps, will reveal a great tract of this earth extending diagonally right across England, from Yorkshire down into Devonshire, where it ends conspicuously in the beautiful red cliffs about Torquay.

There is a large area of the stuff in the Midlands, notably in Warwickshire, with lesser patches here and there about the country.

Second only to the red marls come the brick earths, which, fortunately, are also widely distributed.

"Brick earth" is merely clay that has been well weathered and disintegrated under the action of wind, rain, frost, and organic agents, the sulphides having become oxides, and what was a cold intractable slithery ma.s.s having become merely a "strong" and binding earth.

It is probable that even stiff clay, if dug in the summer or autumn, and left exposed for a winter, would prove sufficiently reformed to be quite amenable for pise building in the spring.

After the marls and the brick earths there is an endless variety of soils that will serve well for pise-building--some, of course, better than others, but all, save the extremes (the excessively light and the excessively clayey), capable of giving good results under proper treatment.

Before putting pise construction actually in hand, however, the intending builder will do well to submit samples of his earth to some competent authority, that they may receive his blessing.

A fistful taken from a depth of 9 in., and another from say 2 ft. below the surface, should give sufficient evidence as to the soil's suitability or the reverse.

III

_CHALK_

-- I. GENERAL

Chalk, as a source of lime, has always been of high importance to builders, and, until improved transport brought alien materials into its old preserves, chalk was in general use for walling in the form of roughly squared blocks.

Chalk again forms the basis of a compost that, used in the form of a stiff paste, has been largely employed for building from the earliest times down to the present.

"Pise de Craie," or chalk consolidated by ramming within a casing, is a form of building that has been long held in high repute in France and elsewhere, but which has only recently been given a serious trial in England.