Everything about Whitewash totally explained
Whitewash, or
calcimine,
kalsomine, or
calsomine is a very low cost type of
paint made from
slaked lime (calcium hydroxide) and
chalk (whiting). Various other additives have also been used.
Whitewash
Whitewash cures through a reaction with
carbon dioxide in the atmosphere to form
calcium carbonate in the form of
calcite, a reaction known as
carbonatation.
When the paint initially dries it's uncured, and has almost no strength. It takes a period of anything up to a few days, depending on climate, to harden.
It is usually applied to exteriors. Occasionally it's colored and used on interiors, such as the hallways of apartment buildings, but it isn't popular for this as it can rub off onto
clothing to a small degree.
Whitewash is especially effective on
adobe-like materials because it's absorbed easily and the resultant chemical reaction hardens the substrate. Also whitewash and
adobe are both very low cost building materials.
The coating has antimicrobial properties that provide hygienic and sanitary benefits for animal
barns.
In the middle of the 20th century, when
family farms with
dairy barns were common in the
Upper Midwest of the
USA, whitewash was a necessary part of routine barn
maintenance.
Limewash
Lime wash is pure slaked lime in water. It produces a unique surface glow due the to
refraction of
calcite crystals. Limewash and whitewash both cure to become the same material.
When limewash is initially applied it has very low
opacity, which can lead novices to overthicken the paint. Drying increases opacity, and subseqent curing increases opacity again.
Additives
Additives that have been used include
water glass,
glue,
egg white,
Portland cement,
salt,
soap,
milk,
flour,
earth,
blood.
Whitewash is sometimes coloured with
earths to achieve colours spanning the range of
broken white,
cream,
yellow and a range of
browns.
Historically pig's
blood was added to give the colour
Suffolk pink, a colour still widely used on house exteriors in some areas of the UK. Animal blood also further reinforces the earth based substrate to some degree.
Pozzolanic materials are occasionally added to give a much harder wearing paint finish. However paint with these added has a short open time, so pozzolan can only be added at point of use.
Linseed oil is sometimes added (typically 0.5-2%) to improve adhesion on difficult surfaces.
Cement addition makes a harder wearing paint in
white or
grey. Open time is short, so this is added at point of use.
Dilute
glues improve paint toughness.
Wheat flour has been used as a strength enhancing binder.
Salt is usually added to prevent the flour going
mouldy later in
damp conditions. The use of salt brings its own issues.
Cost
Simple lime paints are very low cost. A 25kg bag of lime makes around 100kg of paint, and costs around £6 in the UK (2008).
Further Information
Get more info on 'Whitewash'.
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