Cottage Building in Cob, Pisé, Chalk and Clay: A Renaissance (2nd edition)

by Clough Williams-Ellis

COB PICK
(Measured from example at Great Fulford).

Building.—In building a man stands on the low base-wall, and lays the material handed up to him on the cob picks, treading it into position. Thorough treading is important, and the heels should be well used. The material is allowed to project each side an inch or so beyond the stone base to allow for paring down afterwards. The courses are usually about 2 ft. high. The cob should be laid and trodden in diagonal layers, as shown in the diagram: this is to secure proper bonding. It takes from two to three weeks for a course to dry, according to the weather, and five or six men would be required to build the walls of an ordinary cottage. This would not keep them continuously employed, however, and they would require to have several buildings in hand at the same time, so as to be able to turn from one to the other while the courses were drying.

COB COURSE, OR SCAR, SHOWING DIAGONAL LAYERS.

At the completion of a course the corners are plumbed up from the stone base below, a line is stretched through and the wall is then pared down “plumb” with the “paring iron” by the man standing on the wall. Sometimes, however, the paring down is left until the wall is finished and dry. Four men will do about four perches per day of a wall 2 ft. thick, preparing and laying material.

The material is rarely laid between timber shuttering as in Pisé work, as the retaining boards tend seriously to retard the drying out.

PARING IRON
(Measured from example at Great Fulford)

Drying.—If a course takes from two to three weeks to dry, it naturally takes a long time for a whole cottage to completely dry out. The walls can be built from about March to September. The internal fitting, plastering, etc., can be done in the winter, but the external rendering must not be done for at least a year, perhaps two years, to allow the walls to become perfectly dry.

As unprotected cob is sensitive to frost, especially if not thoroughly dried out, it should be given a good external rendering as soon as it is really dry, and should in the meantime be protected from frost by some temporary covering, straw-matting or what not. Also all cob-work must be protected from the rain both whilst building and when built.