Whitewash, or calcimine, kalsomine, calsomine, or lime paint is a very low-cost type of paint made from slaked lime (calcium hydroxide) and chalk (whiting). Various other additives are also used. The incident of Tom Sawyer whitewashing a fence as punishment is a famous image in American literature (written in 1876).
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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 is uncured and has almost no strength. It takes up to a few days, depending on climate, to harden.
It is usually applied to exteriors; however, it is traditionally used internally in food preparation areas, particularly rural dairies, for its mildly antibacterial properties. Occasionally it is coloured and used on structures such as the hallways of apartment buildings, but it is not popular for this as it can rub off onto clothing to a small degree. In Britain and Ireland whitewash was used historically, both externally and internally, in workers' cottages, and still retains something of this association with rural poverty. In the United States, a similar attitude is expressed in the old saying: "Too proud to whitewash and too poor to paint", with the connotation that whitewash is a cheap imitation of "real" paint.
Whitewash is especially effective on adobe-like materials because it is absorbed easily and the resultant chemical reaction hardens the medium. Also, whitewash and adobe are both very low cost building materials.
Whitewash is applied to trees, especially fruit trees, to prevent sun scald.[1] Some also claim that it helps prevent insect damage. Most often only the lower trunk is painted. In Poland painting the whole trunk is also said to help keep the body of the tree cool in late winter/ early spring months and hence help prevent fruit trees from blooming too soon i.e. when warm sunny days could promote rapid tree warming, rising sap and bloom and intermittent frosty nights could damage outer tree rings and destroy the young buds and blossoms.
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. A traditional animal barn contains a variety of extremely rough surfaces that are difficult to wash and keep clean, such as stone and brick masonry, and also rough-cut lumber for the ceiling. Left alone these surfaces collect dust, dirt, insect debris and wastes, and can become very dirty. Whitewash aids in sanitation by coating and smoothing over the rough surfaces. Successive applications of whitewash build up layers of scale which flake off and in the process remove surface debris with it. The coating also has antimicrobial properties that provide hygienic and sanitary benefits for animal barns.[2]
Typically the farm whitewash application is an annual process and has the following steps:
Nonremovable electric equipment is often enclosed in protective outer shells that prevent whitewash intrusion. For example circuit breaker panels may be enclosed within wooden cabinetry which keeps the whitewash spray coating from entering the panel.
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 subsequent curing increases opacity again.
Additives that have been used include water glass, glue, egg white, Portland cement, salt, soap, milk, flour, soil.
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 medium to some degree.
Pozzolanic materials are occasionally added to give a much harder wearing paint finish. This addition, however, creates a short open time, and therefore requires timely application of the altered paint.
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. However, the use of cement restricts the breathable aspects of the limewash; Cement should not be applied to historic buildings in general.
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, such as deterioration of brick and stone.
Simple lime paints are very low cost. A 25 kg bag of lime makes around 100 kg of paint, and costs around £6 in the UK (2008).