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Limewash
Traditionally limewash was the principal finish applied externally
and internally to historic buildings, quite often applied
directly to the masonry or brickwork and more commonly to
pre-applied lime coatings (i.e., harling, plaster, render
etc.,). Although often thought of as a decorative coating,
the limewash was first of all a protective layer to the lime
coatings and masonry substrate. On new lime renders and plasters
it unifies and protects the surface particularly while strength
is developing within the new plaster.
As with all lime coatings, limewash is a breathable coating
allowing evaporation of moisture and water vapour. Limewash
is also a repairing material, being used to fill small shrinkage
cracks on the lime coverings. Limewash can also be used in
conjunction with various aggregates to make shelter coats
for friable masonry and will act as a sacrificial protective
coat.
Plain Limewash
Plain un-coloured limewash will take on the colour of the
lime used; this can range from pure white through to gray
or buff coloured.
Coloured Limewash
Generally earth pigments were used to colour the limewashes,
most commonly ochre’s, but also sienna’s and umbers,
which produced a range of yellows, reds and oranges. Broadly
speaking these produced pastel shades, although deeper colours
are not uncommon. Coal dust, ash, blood and ground stone dust
have all been found as additives in historic limewashes to
achieve the desired colour.
Application of Limewash - Preparation
Surfaces to be limewashed must be clean, free from grease
and they must be porous. Previously limewashed surfaces must
be well brushed down and any loose limewash scrapped off.
Any mould should be treated with fungicide and thoroughly
washed off with clean water. Do not use fungicides, which
contain silicon.
Damping Down
Limewash should never be applied to a dry surface, as this
will cause rapid drying out of the limewash and result in
dusting. Spray about 3 sq/m of the surface to be limewashed
with water until the surface is damp but not running with
water. Do not try to damp down the whole wall or ceiling at
one time, as most of the area will be dry before it can be
limewashed. Dry joints must be avoided as these will result
in the limewash gaining a patchwork appearance.
Application
Limewash is best applied by using a flat brush or masonry
paintbrush. Stir the limewash well before and during application,
apply working the wash well into the surface. The limewash
should be applied in several thin coats. Avoid runs or drips
running down the face of the work.
The limewash will appear transparent when first applied so
care must be taken not to build up the limewash too quickly
as this will craze on drying. Each coat should be allowed
to dry before the next coat is applied. We recommend 24 hours
between coats. It is very important to rewet the previous
coat before applying the next coat. At least 4 coats will
be needed to cover new work.
Each coat will need to be burnished into the surface with
a dry brush as it starts to ‘gel’. This will give
a surface free from brush strokes and leave a unified finish.
As earth pigments are a natural product slight variations
in colour do occur. We highly recommend when ordering coloured
limewash order the whole amount required plus 15%, this should
then be mixed together in a large container and will avoid
variation in colour over the job.
Common Mistakes and Solutions
Limewash dry but powdery: Dried too fast, spray with water
and re coat with limewash.
Limewash not absorbed: Unsuitable non-porous surface remove
and use alternative product.
Limewash patchy Insufficiently mixed, mix following coat thoroughly.
Limewash dries too quickly: Remove flaky limewash and damp
down the background.
IT IS VERY IMPORTANT THAT THERE IS NO DANGER OF FROST
FOR SEVERAL WEEKS AFTER THE LIMEWASH HAS BEEN APPLIED.
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The Building Lime Company | Tel: 01980 611950 | Fax: 0845 658
7788 |