THE THEORY OF PISÉ
The Swedish scientist, Mr. Karl Ellington, of Nossebro, who is basing a book on pisé (in his own tongue) upon the frail foundation of the present volume, has, in the course of a letter to the author, made some exceedingly suggestive “guesses at the truth.”
“I am very interested to hear that you are proposing to use an hydraulic rammer for making blocks. I have thought a good deal about this pressure business. I am trying to scrutinise the thing from ‘the inside,’ so to speak. I am trying to trace out how Nature makes rock. That helps us to understand pisé. Nature made all the stratified rocks out of what was once fine loose earth and mud. Rivers carried the mud out to sea. Waves pounded and gnawed the shores and got down some more stuff. The tides went forth and back and shovelled and levelled at the sea-bottom. Some more mud on top of that, and a few hundred or thousand feet of the heavy water on top of that—and Nature’s pisé was in its making. But why do these mud particles stick together for ever even after that stratum is raised up high above the sea and the pressure is discontinued? That is the counterpoint of the whole problem. What is gravitation? Is it some form of magnetic or electric energy? We don’t know. Do particles of mud grip and hold each other if they are forced together close enough to be united by some sort of magnetic or electric energy? Or do the particles only get a ‘mechanical’ grip on each other? However that may be, we seem to know now that we can make them grip by bringing them closely together. It would seem important, then, that we must bring as much of particle surfaces together within any given cubic space as we possibly can; that is, we must have as little of ‘holes,’ ‘empty spaces,’ pores and channels as possible in the mass, in the pressed wall. This, then, would in turn make it important that plenty of very fine (small) particles must be present in the mass—and so well distributed among the coarser particles as to be on hand close by wherever there can be one more chance for a small particle to fill a little chamber that the coarser particles would like to bridge over. We can think of how well Nature was fitted for this work of shuffling over all the particles at the sea-bottom and under great water pressure till she got every particle into the niche where it would exactly fit. She used waves, tides, and gulf streams as shovels and mixers and packers, and the water above as ‘hydraulic rammer.’ Looking at the pisé matter in this way, it would appear that both the mixing and the shuffling are of vital importance. And by ‘shuffling’ I mean in this connection only that the smaller and larger particles get a chance to shift over a little during the process of pressing the earth together to hardness, so that the pressure may not work only and exclusively in a straight downward direction, but in a sort of wavy zigzag direction as well—much as when a street-roller is working the macadam and gravel a little forth and back at the same time as downward. I have a great respect for old tools which are the outcome of long-time experience and handed-down wisdom. I suspect the presence of some of that sort of experience in the rammer described in your book, p. 59. That tool would do the necessary shifting while attending to its main intention: hammering the mass solidly together downwards. Now for your hydraulic rammer—is it advisable to make it blow or press only in a straight line downward? Maybe there ought to be two or three kinds of strokes alternating—one stroke with a rifled or wavy surface under the rammer—and the next stroke with a plane surface. . . . What sort of witchcraft enters into the effect of high frequency blows as compared with blows with a little longer intervals between? Do the strokes create also some ‘magnetic’ effect in the pounded earth-mass which helps to fasten the particles to each other? And does this magnetic charge or friction heat, or whatever it is, act more promptly if one keeps on ‘striking the iron while hot,’ instead of letting the charge ‘evaporate’ and sneak away between strokes? Two or three of my hairs are turning grey over these questions alone. You compliment me by insinuating that I might stumble across some fruitful idea for the forms or boxes if I speculate a little more on the key-problem. Well, the thing won’t leave me alone, so I have thought out several foolish variations and rejected them too. But the last one seems to have a little more vitality, so if it will live till I write my next letter I will tell you about it. One is so apt to follow the temptation of ‘perfecting’ an apparatus—at the cost of getting away from keeping it cheap, simple—and ‘fool-proof.’ By this time the idea has grown ripe in my mind, so that I ought to write out a little book on the pisé problem in Swedish and have it printed before springtime. Something ought to be done. . . . I have to ask you kindly to permit me to make use of the data contained in your book. To this I will have to add what special precautions we must observe as to foundations in a climate like ours. I intend to treat only the pisé method. Cob and chalk methods are not applicable here, as we have such materials only in a few unimportant spots.”
Mr. Ellington has long been an admirer and a firm friend of England, and he is good enough to regard his country as indebted to ours for the introduction of pisé-building:
“Let me tell you that the help you are giving me now—not me, but my nation—will work as an additional bond that draws us more closely towards each other. . . . Some of our people here have always looked too much towards the South and too little towards the West.”
A Pisé-Builder’s School
PISÉ, PRACTICE AND PLANT
Now that so many able architects and enterprising bodies are seriously taking up pisé-building, the improvement in plant and technique should be both rapid and considerable. The School of Pisé Building established at Hornchurch in Essex, by the Imperial Ex-service Association, 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 pisé “Test-House,” built by Messrs. Alban Richards at their Ashstead works, was built in this way, and proved highly satisfactory.