whitewash

whitewash

[hwahyt-wosh, -wawsh, wahyt-]
whitewash, white fluid commonly used as an inexpensive, impermanent coating for walls, fences, stables, and other exterior structures. It varies in composition, being generally a mixture of lime (quicklime), water, flour, salt, glue, and whiting, with other ingredients such as molasses, water glass, or soap sometimes added. Mixed with size and colored, whitewash is occasionally used on interiors as calcimine.
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 is 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 is colored and used on interiors, 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.

Whitewash is especially effective on adobe-like materials because it is 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).

References

External links


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