The Decorative and Protective Roles of Limewash
While the romantic magic of limewashed buildings amazes many of
its admirers to-day, limewash was common place as a protective and
decorative treatment for at least ten thousand years.
limewash is a mixture of slaked lime (calcium hydroxide) in water
which sets slowly by absorbing carbon dioxide from the air. The chemical
reaction which occurs produces crystals of calcite (calcium carbonate).
These crystals are unusual in that they have a dual refractive index;
light entering each crystal is reflected back in duplicate. This results
in the wonderful surface glow that is characteristic of limewashed
surfaces, and is not found in other decorative finishes.
when limewash was discovered, man was not looking for a decorative
finish to impress the neighbours. He had actually discovered a sacrificial
treatment which protected his dwelling against the worst weather.
Early mud structures and wattle and daub panels were very vulnerable
to the climate and limewash still plays a most important part in protecting
these surfaces in particular.
to the patenting of Portland cement in 1824, most structures were
constructed of solid, porous materials which keep out damp and rain
through their thickness and their high porosity or vapour permeability;
that is to say that they dry out so quickly that damp never penetrates
the thickness of the wall. Rapid drying was aided by the use of open
fires, and the kitchen fire in particular, which remained alight throughout
the year, providing both heating and ventilation. Some idea of the
rate of ventilation this provides can be gained by watching the rate
at which smoke pours out of a chimney, as air is drawn into the building
at exactly the same rate. This marvellous ventilation ensured that
any moisture present in the building was expelled through the chimney
within a very short time.
assists in maintaining the ability of the building to breathe as it
is one of the most vapour permeable decorative coatings. Tests show
that limewash has a vapour permeability rating of about 350 units
while many of the masonry paints are well below a rating of 75 units.
If a building is prevented from breathing, water can become trapped
in the external walls, resulting in the decay of the masonry and producing
ideal conditions for timber rot to commence. Condensation may take
place and heating bills rise as a damp wall transmits heat faster
than a dry wall.
THE MATERIALS USED
Prior to the introduction of Portland cement, lime putty was the principal
binder in mortars, renders and plasters. It was therefore logical
that the same material should be used as a finish on lime plasters
and renders. Its use internally on plaster is mainly decorative but
on external renders its protective qualities are essential.
putty is made by burning limestone or chalk (both forms of calcium
carbonate) to produce quick lime (calcium oxide), which is then 'slaked'
by adding water. Traditionally, limewash was produced mainly from
lime derived from the purer sources of limestone, as limestones contaminated
with clay may produce an 'hydraulic' lime when fired which sets by
reaction with water.
was often added to limewash to make it water droplet resistant while
retaining most of its quality of vapour permeability. A type of animal
fat, tallow was primarily used with beeswax for making candles, and
was therefore widely available. ('The butcher, the baker, and the
candlestick maker': as the nursery rhyme suggests, even the smallest
village had a candlestick maker ie a source of tallow). More recently,
raw linseed oil was added for the same purpose. Other alternatives
used nowadays include casein which increases the vapour permeability,
resists dusting and being a weak form of adhesive, may be useful when
decorating difficult surfaces. Although, historically, sea water was
used during the slaking process in the eastern counties, and common
salt may be added to limewash to reduce dusting, the practice is seldom
used today due to the importance of keeping salts out of the fabric
of the buildings.
colourwashes (coloured limewashes) care should be taken in selecting
watersoluble pigments to ensure that they are not affected by ultra
violet light nor by lime. A variety of earth pigments are available
and these should be soaked for at least 24 hours before being incorporated
into a wash. These are essentially refined earth or clay with a strong
natural colour, such as red and yellow ochres. The colour is given
by their mineral content and they are therefore least likely to fade
in the sunlight or by chemical reaction with the lime.
MAKING A LIMEWASH
Limewash is not difficult to produce providing that a few simple but
important rules are observed.
slaked the quicklime, the resulting putty should be left for at least
three months to ensure that all the quicklime has reacted with the
water and that the particles of lime have started to mature.
putty should be sieved to exclude any foreign material as even the
finest and purest naturally occurring limestone will contain some
should be applied as thinly as possible to facilitate carbonation
and prevent crazing that can occur when applied more liberally and
it is therefore recommended that the putty is diluted with sufficient
lime water (that is, water that has been saturated in lime putty)
to produce a wash the consistency of milk. Providing that it is thin,
there is little likelihood of an over enthusiastic operative applying
too thick a coat.
this basic limewash may be added binders such as raw linseed oil which
will help it to adhere by making it moisture droplet resistant while
remaining vapour permeable. In the event that tallow is to be added
this can only be effectively included during the slaking process.
While there has been a long tradition of tallow in limewashes, its
use on interior walls is not to be recommended, as it is liable to
become rancid in warm weather.
a water based product, limewash is most suitable for application onto
an absorbent background. Traditionally it was applied to earth walls,
brick, limestone and calcareous sandstone, lime render, plaster and
timber and, having found that the mildly antiseptic properties of
lime would help to prevent the spread of disease, farmers regularly
limewashed calf pens between batches of calves.
those trying to produce a colourwash for the first time it will be
rather disconcerting to find that having made what appears to be the
appropriate colour in the tub, it dries many shades lighter once it
is applied. Colours need to be dry tested to ensure the correct hue
has been achieved. Furthermore, it is almost impossible to reproduce
exactly the same colour if a further supply is required for the same
job. After all, this is a hand-made craft product and slight variations
are inevitable and appropriate.
When making or applying limewash, safety goggles or glasses and gloves
should always be worn. Lime is irritating to skin and, in contact
with the eyes, may cause pain and impairment of vision if not treated
with so many jobs, good preparation is important. The background should
be absorbent; inappropriate old paint treatments should be removed;
and, if paint stripper is used, a check should be made to ensure that
the pH of the surface has not been radically changed. Insufficient
washing down after the use of an acid based solvent, for example,
may leave the surface sufficiently acidic to interfere with the limewash,
resulting in failure. When rejuvenating an old limewashed surface,
care must be taken to remove any loose or spalled material and the
entire surface should be thoroughly washed down using a soft scrubbing
brush to ensure that the dust is removed. All surfaces to be limewashed
should be wetted with clean cold water and left until the surface
is damp but not wet.
best results are obtained when the limewash is almost scrubbed into
the surface with a brush which is stiffer that a conventional paint
brush but softer than a scrubbing brush, such as a soft bristle dustpan
brush (which costs only a couple of pounds). The application should
be with a circular motion, ensuring that the limewash is worked into
the surface and spread as far as possible. The work should be finished
with vertical strokes.
cures by absorbing carbon dioxide from the atmosphere and this process
is prolonged during periods of low temperature or high relative humidity.
Even though the application has been kept as thin as possible, it
may take several days before it can be safely overcoated. It is advisable
to leave it for at least five days before further work is carried
should be taken to choose a period of fine weather before applying
limewash externally as a fresh coat is vulnerable to dilution by rain
which will manifest itself as white streaks running down the work
or the colour washing out. Should this occur, all is not lost as once
this coat has cured a further coat will cover the damage. Further
dismay may be experienced by the newcomer to limewash when the first
coat is applied and appears very thin and almost without any body
or depth. Reassurance is close at hand when after only a few hours,
the cure starts and the depth and vibrancy of this material begins
to show. After a further coat has cured you will be as enthusiastic
about the material as we are. It is recommended that a minimum of
three coats should be applied for new work.
Ashurst, John and Nicola, Practical Building Conservation Volume 3, Mortars, Plasters and Renders. English Heritage, Gower Technical Press, Aldershot, 1988
Jane Schofield, Lime in Building, Black Dog Press, Crediton, Devon, 1995
article is reproduced from The Building Conservation Directory, 1997
BENNETT is a masonry consultant specialising in the care and
repair of historic buildings and is a founder member of the Building
Limes Forum. In 1990 he opened The Lime Centre to provide practical
day courses in the use of lime and to supply specialist materials
including limewashes. Besides a regular programme of courses each
year, he also travels widely within the UK and overseas, teaching,
advising and troubleshooting.
Lime mortars and render
Paints and decorative finishes
PRODUCTS AND SERVICES
Lime, non-hydraulic (lime putty)
Paint and decorative finishes
Communications Limited 2010