The Successful and Safe Application of Lime Washes
General Guidance Notes
Buildings such as these are constructed using solid walls with two skins of (sometimes) dressed stone with a rubble core fill between. They are unlikely to contain damp-proof courses and will always contain varying degrees of moisture, dependant on the time of year and the overall condition of the fabric, i.e. how good is the pointing? Are there leaking rainwater goods etc? Moisture must be allowed to migrate freely through these walls to evaporate, and this is best achieved using lime based mortars, renders and paints. Changes in temperature and humidity will often result in condensation, and a porous, absorbent finish is desirable to prevent the walls "running" with water.
Research carried out at all levels has proven limewash to be the most permeable type of decoration known, allied to the fact that it has been used as a decorative finish for "hundreds" of years throughout the world, it is beyond doubt a tried and tested product.
With limewash the material being applied to the wall surface is calcium hydroxide (suspended in water). Following application the water evaporates and atmospheric carbon dioxide readily combines with the wash to form calcium carbonate, a process known as carbonation. During the carbonation process the limewash hardens, develops its colour and makes it bond to the substrate forming what is in fact a thin sheet of limestone on the surface.
The most important part of the carbonation process is not to allow the limewash to dry too quickly.
The application of Limewash should be avoided in the following conditions.
Strong drying winds or under strong direct sunlight. If works have to continue under unfavourable conditions measures should be taken to protect the works (fog misting with a spray).
Limewash is normally applied to a sympathetically porous substrate, such as lime plaster, clay bricks, soft stones etc. It is not likely to work on impervious surfaces. Its use on timber although practiced is in the past should be carefully questioned today.
Surfaces should be clean and free of grease and vegetable matter such as lichens etc. All loose or flaky material should be removed.
Any organic growth should be treated in an appropriate manner (possibly using a suitable biocide in accordance with the manufacturer’s instructions) with all dead material being removed prior to lime washing.
Regulate work to one coat a day, allowing individual coats time to carbonate, as re-coating to soon may result in the previous coat pulling away and hamper proper carbonation. Apply limewash using a large long hair brush. Application should be vigorous using horizontal, vertical and diagonal strokes, ensuring the wash is applied thinly and evenly. Working in areas of say 1m2 work the limewash into the surface by scouring with the brush in a circular motion. Limewash should always be carried out in a manner where you are following a wet edge in order to avoid scarring and lines from a build up of material. If applied to thick or heavy this can result in crazing and cracking, if this should occur and the results are unacceptable, wash off with hot water and a stiff bristle brush.
Ready mixed Limewash is supplied in plastic containers; upon opening the drum mix thoroughly using appropriate tools CLC sell mixers that you attach to an electric drill that are very useful however, a simple stick will obviously be effective. Simply stir vigorously until the con-tents are one and continue to do so every ten to fifteen minutes during application, the last brush-full from the tub should be as thin as the first.
Health and Safety COSHH Assessment
Limewash is alkaline so every effort must be made to prevent any from getting into ones eyes, in the event of this happening rinse the eye(s) thoroughly for several minutes, should discomfort continue seek medical attention straight away. It is advisable to keep a bottle of proprietary eyewash to hand for irrigation purposes.
The wearing of gloves along with other Personnel Protective Equipment is advised as limewash is alkaline and it can dry the skin along with more serious dermatological effects.
There are no risks from fumes, vapours or burning when heated. By virtue of the way it should be applied lime washing can be a messy operation and the wearing of overalls or similar along with adequate protection of fittings is advised. Splashes should not be left too long before wiping up.
For further information, please Contact Cornish Lime or phone: 01208 79779