Goat Hair
Hair is added to plaster when it is applied over laths or wattle. The hair binds the plaster together and ensures it forms a coherent mass on the ceiling or wall. The hair itself should be about 40mm (1.5 - 2 inches) long and tough. Thorough mixing into the plaster is essential to ensure consistency and no 'rats tails' of tangled hair. It is best mixed in just before the plaster is to be used. The easiest way to mix it in is by sprinkling it evenly over mortar which has been spread out flat. Then turn the mix over several times.

Linseed Oil/Tallow/Casein
Linseed oil can be added in small quantities (1 to 2.5% by volume) to improve the weathering of limewash. Tallow (animal fat) was traditionally added to limewash for the same purpose. Casein (protein from milk) can be mixed with limewash to improve binding and can be mixed with lime putty to make a strong adhesive for both stone and wood.

Pozzolanic Additives
Pozzolans are naturally or artificially fired clays which are reactive when mixed with lime. Pozzolans are added to lime mortars to provide extra strength. To ensure maximum effect the pozzolan must be very fine and thoroughly mixed into the mortar. You would usually need approximately 1 part of pozzolan for every 9 parts of mortar (by volume). This must be done only just prior to use as the mortar will start to set once the pozzolan is added.

Pigments
Pigments are added to limewash to produce a coloured limewash. Earth pigments are most commonly used to produce a wide range of beautiful colours ranging from pale creams and pinks to strong yellows, dark purples and rich browns. The pigments are added when the limewash is made. The amount of pigment will vary with the depth of colour you require and can be determined by experimentation.

Sand/Stone Dust
Sands and Stonedusts are mixed with lime putty to form mortars, plasters and renders. Sands are usually mixed and graded at the quarry to satisfy British Standards. It is important that the sand is well graded and angular. Stonedusts are usually crushed and sieved limestone. Stone repair mortars and sheltercoats usually have a higher proportion of stonedusts whereas construction, pointing mortar and plasters and renders have a high proportion of sand.

See the sections on making mortars, plasters and renders to find out how much you will need.