Chalk Compost: Historical.—At the Ancient British village on West Down, Chilbolton, some five miles south of Andover, delving archæologists have brought to light undeniable fragments of chalk “Daub,” with the wattle marks still clearly showing upon them.
This discovery is chiefly of academic interest, though it is a pretty refutation to those who regard any building material save brick and stone as “new-fangled,” and it should also serve to hearten the doubters and the timid amongst us who seek historic sanction for any departure from current building practice.
Composition and Uses.—In the Andover district Chalk Compost or “Chalk Mud,” as it is called locally, is prepared and used as follows:
The chalk is dug out in the autumn, and the frost allowed to play on it during the winter. In the spring building starts, and the weathered chalk is spread all around the outside of the walls. Straw is sprinkled on it and it is then well trodden, usually by the workers, but sometimes by horses. Sometimes chopped straw is added, sometimes unchopped straw is sprinkled on. The quality of the walls depends very largely on the preparation—that is, in getting the mud to the right consistency—and the old hands know by experience when it is ready.
The compost is lifted on the wall by a fork and another man stands on the wall and treads it in. It is then chopped down straight with a spade. Some of the naked walls at Andover show traces of the courses, which are usually something under 2 ft. in height.
Where a course has to be left unfinished it should be ended with a diagonal ramp so as to splice in with the work that follows.
Some of the old builders seem to have been somewhat catholic in their conceptions as to what constituted “chalk,” and vague patches of earth, loose flints and other stray substances not infrequently mar their work and sometimes seriously reduce its strength.
As a general rule, the finer the chalk the stronger and more durable is the walling.
What is aimed at is a conglomerate of small chalk knobs cemented together by a matrix of plastic chalk and straw, the whole forming as dense a mass as possible.
Grinding in a mortar-mill would probably reduce all the chalk to an amorphous powder, which would not be desirable, and in any case such mechanical mixing is quite unnecessary.