Rats.—Where the surface rendering of cob-walls has been omitted or has been allowed to fall away, an enterprising rat will sometimes do considerable damage by his tunnelling.
A little powdered glass mixed with the lower strata of a wall will discourage any such burrowing, but the best preservative for any cob building is a thoroughly good skin of rendering, especially if this be reinforced by fine-mesh wire-netting secured to the wall.
Strength.—The strength of cob walls is surprisingly great so long as they are vertical, and are not subjected to undue lateral thrust or tension.
Beams as large as 12 in. by 12 in. may be seen supported by old cob walls, and there is nothing likely to be asked of the material in the way of strength to which it cannot easily respond.
Design.—Cob, like every other material, should have a certain say in the design of any building in which its use is intended.
The chief desiderata are a plain straightforward plan and broadly treated elevations where voids and solids are carefully disposed with an eye to getting as large unbroken blocks of cob as possible.
Cob House temp. Elizabeth, Lewishill.
Walls from 3 ft. to 4 ft. thick. A wing was added in 1618. This farm has been occupied by the family of the present holder between 300 and 400 years.