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First Coat - The Render or Scratch Coat
The composite of the mixture of sand and lime can be anything from 3:1 to 1:2 but generally tends to be 2-3
parts sand to one part lime with the amount of animal hair (usually horse, cow, goat or Yak) governed by the cubic
metre of mortar.
The animal hair is not introduced until about 24 hours prior to application as the alkaline
in the lime attacks the protein in the hair and weakens the fibres and will affect the very integrity of the building.
The hair used is long and strong and free from grease, lumps and clumps. To test consistency it should be clearly
visible as a beard around the edge of a trowel full of mortar when inverted.
When working on the hard (i.e.
to stone or brick) the first coat of mortar is thrown hard at the surface then spread with a laying-on trowel onto
a dampened but not wet background at approximately 9-12mm thick. For application on to laths it is applied as evenly
as possible and pressed firmly between the gaps to form rivets between and behind the wooden laths. The surface is
then "keyed" using a broad tooth scratcher to give wide indentations on the surface in preparation for
the next coat.
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