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. 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.
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 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 an 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.
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 even further.
The blue laundry dye (such as Reckett's 'Dolly Blue' in the UK, Ireland and Australia, Loulaki in Greece, or Mrs. Stewart's Bluing in North America) formerly widely used to give a bright tinge to boiled white textiles was a common 19th Century addition and gives a pale blue paint.
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. Excessive animal blood (iron oxide) can compromise the lime binder's strength.
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.
Basic limewash can be inadequate in its ability to prevent rain driven water ingress. Additives are being developed but these have the potential for affecting free vapour permeability, for this reason silicate paints, more common in Germany, are gaining popularity in the UK over limewash.
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).
In popular culture
|Look up whitewash in Wiktionary, the free dictionary.|
- Lighthouse keeper's formula for White Wash at Crisp Point Light.
- Paper on Whitewashing including mixes etc by Peter Mold & Richard Godbey