Cob: hair and render

[Brad Calvert]

from:
http://www.southsomerset.gov.uk/agenda21/buildingcons/lime%20book/mixplas.htm

it says:

"When plastering onto lath it is essential to add hair to the mix to help in
forming a key of plaster between the laths. Whilst it is not essential to
use a haired mix for other backgrounds it can help to reduce shrinkage. Goat
and cattle hair are preferable to horse hair which is too slippery. Hair
should be added to the mix just before use. Do not add hair to coarse stuff
that is to be stored for more than about six weeks as the hair may rot if
left in damp lime mortar for a long time. The hair should be gradually
teased into the mix so that it is well distributed and does not form clumps
(often referred to as 'dead mice'). As a rule add one pound of hair per
three cubic feet of mortar for walls and one pound of hair to two cubic feet
of mortar for ceilings. For the second coat halve the quantity of hair. To
check whether there is sufficient hair in the mix, scoop a dollop of mix
into a gauging trowel, tap the underside of the trowel smartly against a
hard edge so that the blob flattens and the surplus mortar falls off the
edge of the trowel. There should be a fringe of hair at 1-2mm intervals
around the edge of the trowel."