Whitewash

This article is about the paint. For other uses, see Whitewash (disambiguation).

3 different brands of Kalsomine, (the directions for use are visible when viewing image at full size)

Whitewash, or calcimine, limewash, 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. The incident with Tom Sawyer whitewashing a fence as punishment is a famous image in American literature.

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 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 anti-bacterial 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.

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.

Farming applications

White-painted trees in Turkey

Whitewash is applied to trees, especially fruit trees, to prevent sunscald. Some also claim that it helps prevent insect damage. Most often only the lower trunk was painted.

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.

Typically the farm whitewash application is an annual process and has the following steps:

• Surfaces that are to be protected from whitewashing are enclosed in plastic sheeting or bags, such as windows, light fixtures, and the milk pipeline in a dairy barn.
• The interior is stripped of all removable equipment leaving walls, floors, and ceiling as bare as possible.
• A high volume compressed air wand (often supplied from a very large engine-driven air compressor suitable for driving a jackhammer) is used to blast away loose whitewash scale from the walls and ceiling. This loose debris is swept into the barn gutter and goes into the manure handling system where it eventually contributes to soil fertility.
• A mobile whitewashing trailer is used to mix the quicklime into a thick liquid, which is then sprayed as a thick even coating over the interior walls, ceiling, and posts, into all accessible nooks and crevasses.
• The coating is allowed a few hours to dry and stop dripping from the ceiling, and the protective plastic coverings are removed. Eventually after the walls and ceilings have dried sufficiently, equipment is brought back into the barn.

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.

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 subsequent 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. 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.

Cost

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).

External links

• Farm recipe for whitewash, with details
• Lighthouse keeper's formula for White Wash at Crisp Point Light.