Limewash

General‍

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 grey 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 recoat 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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Limewash (or other breathable paint finish) is the final part of the protective envelope for structures coated with a lime render either smooth or rough as in the case of harling.

• It provides a protective, permeable and renewable skin of calcium carbonate.

• The best limewash is manufactured from mature lime putty or quick lime.

• Surfaces to be limewashed must be clean and free from grease. The best results are achieved on porous backgrounds i.e. lime plasters and renders. Surfaces and joints should be brushed free of loose dirt with a natural bristle brush (not a wire brush) to ensure a good bond, and open joints flushed out with water. Previously limewashed surfaces must also be well brushed down and any loose limewash scraped off.

• Any mould should be treated with fungicide and thoroughly washed off with clean water. Do not use fungicides which contain silicon. All lichens, moss and vegetation should be removed using a compatible biocide and bristle brush, or a steam cleaner. All forms of biological growth will retain moisture and can grow back through the new coating.

• The area to be limewashed needs to be dampened down with clean water prior to application. Dry porous sandstone will normally have excessive suction. Dampening down, to control suction between the background and newly applied materials is essential. Applying limewash to a dry surface will cause excessive dusting and an unpleasant white bloom on the surface. This is due to rapid drying and the lime being brought to the surface. Spray about 3sq/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.

• Denser, more impervious stones, e.g. whinstone or other metamorphic stones, or some granite have very little natural suction, and lime mortars may not adhere to these stones if there is any surface water present. These low-suction backgrounds need no dampening down.

• Limewash is best applied using a 5 or 6 inch brush working the wash in thoroughly over the surface. It is important to stir the limewash before and regularly during the application.

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• Building up a thickness of limewash using many light coats is the most desirable approach. Apply, working the wash well into the surface. 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.

• A period of 24 hours should be given between coats, to allow the wash to dry. It is important to rewet the previous coat before applying the next coat.

• At least 5 – 6 coats are needed on new work, up to 10 can be added if time allows, building up a satisfactory depth of colour.

• For best results lightly buff up the surface when it has “taken up” a little using a dry worn brush.

• As with all operations using lime products, protection will need to be provided before, during and after application. It is very important that there is no danger of frost for several weeks after the limewash application.

• Limewash should be maintained with further coats every 2 – 4 years depending on exposure.

• The application of limewash is a very important part of the structures protective skin yet many specifications either omit it, or not enough resources are channelled towards it.

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Limewash serves a very functional purpose yet it is also decorative. Plain un-coloured limewash will take on the colour of the lime used; this can range from pure white through to grey or buff coloured. Generally earth pigments were used to colour the limewashes, most commonly ochres, but also siennas 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. When using pigmented limewashes, it is advisable to calculate the total amount and to mix this in one batch. Slight variations in colour are possible between batches.

‍We sell Limewash made from Mature lime putty.

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