All you need to know about limewash
Q. What is limewash?
A. Limewash is a simple type of matt paint made from lime and water, with or without additives. Colours are obtained using alkali-resistant ("lime-fast") pigments, particularly metal oxides from natural earths. Pink is often associated with Suffolk, for example, and vibrant orange with the Lothians. Impurities in early lime commonly produced off-white limewash without additional pigments, not today’s startling white.
Historically, the terms "limewash" and "whitewash" could be interchangeable, but, more recently, the latter has referred to poor quality limewash or a white distemper.
Q. Where might limewash be applied?
A. Limewash has been used externally and internally for centuries, most of all at the vernacular level. It is suitable over lime plaster or render, earth walls, limestone, timber and most old limewash. It takes less well to cement render, plasterboard or emulsion, but may be possible to apply, particularly if modified for better adhesion. Limewash is unsuitable for impervious materials (flint, hard brick, etc) and first-time limewashing is inadvisable on sandstone.
Q. What are the pros and cons of limewash?
A. Importantly for old buildings, limewash has the advantage of being considerably more "breathable" than most modern paints. It can also consolidate surfaces and, unlike with uniform synthetic coatings, provides attractive colour variations, especially after weathering. The alkalinity deters wood-boring beetles and helps sterilise walls. Furthermore, limewash is inexpensive and solvent-free.
The disadvantages are that much care is needed for the best results, matching coloured limewash batches is difficult, and limewashing is less successful in very fast-drying conditions.
Q. Isn’t limewash dusty?
A. Good quality limewash applied properly to a suitable substrate should not rub off readily onto clothes. Reasons for poor adhesion can be preparation with ordinary bagged lime, coats being applied excessively thickly, inadequate dampening down before limewashing, or too rapid drying out.
Q. How do I identify limewash?
A. Besides a typically soft- to medium-toned colour and non-uniform appearance, paint that erodes gently rather than peels may be limewash. A finish that temporarily darkens after rain is also indicative of limewash. Close up, flakes are frequently seen to comprise a series of layers. Samples fizz and dissolve when placed in hydrochloric acid (brick-cleaning fluid). Although greater effort is demanded than with soft distemper, limewash can often be removed with water - unless water-shedding additives are present.
Q. How do I obtain limewash?
A. Diluting lime putty to the consistency of milk produces limewash. Pigment for colouring should be pre-mixed with hot water. As colour-matching is difficult, enough limewash must be made to complete a single coat.
In the past putty was created from quicklime on site, but safety considerations today mean it will generally be purchased pre-made. The alternative of preparing putty from ordinary (non-hydraulic) bagged lime can result in inferior limewash. Hydraulic lime may be used instead of putty, however, for extra durability in wet conditions, or for improved adhesion on less absorbent surfaces. If you prefer not to make limewash yourself, it can be supplied ready-made.
Q. Do additional binders help in limewash?
A. Additional binders are sometimes added to limewash for improved water-shedding or adhesion, but this can be unwise without good justification. Examples are tallow and raw linseed oil but, as with hydraulic limewash, both reduce "breathability". Beware that tallow may also support mould growth without a biocide, as can casein, another possible binder.
Q. How do I apply and renew limewash?
A. Limewash typically requires renewing every five years. Suitable surfaces are brushed down and minor mould growth removed with fungicide. They are then dampened (normally with a hand-pumped spray) and limewash is applied thinly and worked in well, using a large, rough-textured brush. At least three or four coats are usually needed, each preceding coat being allowed to dry and the surface dampened down before the next goes on. Wear gloves and eye protection.
For tinted finishes, pigment is often just added to the last coat or two. Limewash turns much lighter as it dries, so colour trials are recommended!