Often thought of as a decorative coating, limewash is primarily 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 or surface. Limewash is also used as a repairing material, to fill small shrinkage cracks on the lime coverings. It can also be used in conjunction with various aggregates to make shelter coats for brittle masonry and will act as a sacrificial protective coat.
In short – yes, when used externally. It requires regular renewal, typically every two years. The addition of a binder during the slaking stage, such as tallow, casein (both of which are animal derivatives and act as water repellents) or linseed oil will improve the durability. (Linseed oil is a traditional vegetable-based additive and its water shedding properties are considerable, so generally a one per cent solution is all that is required e.g. 50ml to 5 litres of wash)
However, do not use these additives when using Limewash Internally:
Limewash is ideal for internal use as it is unaffected by rising damp which continually breaks down most other paints. Using casein, tallow or linseed oil will reduce absorption and hinder the evaporation of moisture within the internal wall.
If you are unsure and wish to for more detail on this, please feel free to contact us and speak to a member of our experienced team.
The surfaces to be limewashed must be clean, free from grease and they must be permeable to air and liquid. Previously limewashed surfaces must be well brushed down and any loose limewash should be scraped off. Any visible mould should be treated with fungicide and thoroughly cleaned with water. Do not use fungicides, which contain silicon.
Limewash should not 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 (at a time) of the surface to be limewashed with water until the surface is damp but not running with water.
Typically, limewash is best applied by using a flat brush or masonry paintbrush. You should stir the limewash well before and during application and work 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 area.
Earth pigments are used to colour the limewashes, most commonly ochre’s, but also sienna’s and umbers, which produced a range of yellows, reds and oranges. These pigments produce pastel shades, although deeper colours are not uncommon. Coal dust, fly ash, blood and ground stone dust have all been used as additives in limewashes to achieve the desired colour.