Back to the future II
Traditionally the paints that were used by the everyday folk to protect and decorate their buildings were homemade and based on locally available ingredients, such as clay, lime, milk (casein), eggs, blood, urine and earth pigments. They were based on regional traditions and tried and tested recipes, often passed down from generation to generation. For the wealthier classes of society, more expensive and rare ingredients were used to make up the paints. This involved the use of exotic pigments to produce extravagant colours, which were then mixed with expensive oils and resins.
Over the past 80-100 years, the philosophies and materials used for painting buildings have changed drastically. Prior to the advent of mass-manufactured paints from the end of the nineteenth century, paints would be mixed on site with simple ingredients. These produced the traditional paints such as oil and water-bound distemper (water, oil, whiting and natural glues), oil paints (linseed oil, turpentine and pigments), milk paints (casein powder or milk) and limewash (slaked lime and water). This tradition continued, despite the availability of ready-made products, up until the late 1950's.
In the 1950's a quantum leap in the paint industry took place. This was connected to the post-war construction boom. At this time, the first synthetic, petrochemical paint was formulated. These synthetic paints, consisting primarily of synthetic oils and latex, were cheap and simple to produce on vast scales. This meant that the paints described above, made with simple and safe ingredients for hundreds of years were replaced by the chemical formulations that line the shelves of DIY stores throughout the world today.
In recent years there has been a growing awareness of the direct links between these modern paints and major environmental degradation. The links have also been made with these products in creating a range of problems in relation to human health and the health of buildings made out of traditional materials. Because of this there is currently a resurgence in the use of traditional, homemade paints. By making up your own paints from scratch, it is possible to have ultimate control over the ingredients being used to make the paints, as well as the colour and texture of the finish. These traditional paints are by far the most 'green' and safest options available. They are also often the most beautiful and effective when used on buildings made out of 'natural' and traditional materials, which require paints that will 'breathe', allowing a healthy exchange of moisture in and out of the walls.
Limewash - it's composition and properties
Limewash is a simple paint made out of slaked lime, water and natural earth pigments, which are added to a white limewash base, if a coloured finish is desired. These simple ingredients make it extremely cost effective. When well made, it creates a soft, matte effect that complements and enhances old buildings constructed out of natural, 'breathable' materials, such as lime render, cob, wattle and daub, stone and traditional brick. It is often said that limewash produces a unique surface 'glow', especially when earth pigments are added. This is due to the presence of crystals of calcite (calcium carbonate) formed when it dries and cures. These crystals absorb light and then reflect it back in duplicate.
As well as its beauty, the main benefit of using a limewash, especially onto walls made out of porous materials, is its high vapour permeability and hence its ability to dispose of water, whether from rising damp, condensation or exterior rainfall. This is due to its micro-porous structure, ensuring that any moisture absorbed into the outer skin of the limewash or plaster/render is able to quickly and efficiently evaporate. This enables the walls to effectively 'breathe', and hence prevent the accumulation of excessive and harmful moisture build up within the structure. This also makes limewash the ideal finish for use in remedial situations in old buildings where dampness is an issue. Limewash will also successfully heal minor shrinkage cracks in the plaster/render, as well as even out blemishes in the wall surface, especially when numerous coats are applied to build up protection. Limewash is also flame resistant and will prevent the spread of flames. It can be made washable if made well, and is not affected by ultraviolet light.
Areas of application
Like a lime plaster or render, a limewash dries into a water insoluble finish, meaning that it will not wash off in the rain. This makes it suitable for use on both internal and external walls. Additional ingredients, such as linseed oil and casein, however, can be included to a basic limewash mix to enhance its effectiveness on external walls that are exposed to severe weather conditions (see box). It is also possible to vary the type of lime used to achieve different properties in the finished paint. A fresh coat of limewash will often need to be reapplied yearly to external walls, depending on exposure. Internally, it will not need renewing as often. However, a fresh coat can do wonders for brightening up a space, as was the traditional practice during the yearly 'spring clean'.
Because limewash is water soluble, it is most suitably applied onto walls or backgrounds that are porous and hence water absorbent. It will therefore probably not bond to an existing 'plastic' emulsion. The ideal background is a freshly applied lime plaster or render. This ensures maximum bonding, colourfastness and durability. When applied onto newly plastered/rendered walls up to five coats will be needed to achieve adequate depth of colour and levels of protection to the walls. Limewash can be applied onto wood as long as it is unvarnished and free of polish. This traditional practice involves painting a coat of limewash onto the wood, and then brushing it off. This rubs the limewash into the grains of the wood leaving a pleasant and subtle finish.
Basic limewash with putty
Use as a general limewash for inside and outside.
N.B. Wear protective clothing and goggles.
Ingredients:
- 1 part mature lime putty (minimum 3 months, 6 months to 1 year old for best quality)
- 3 parts clean water
Mixing:
1. Fill bucket 1/3 full with lime putty.
2. Add water gradually and whisk together using a paddle attachment onto a drill, until the consistency of full fat milk is reached.
3. Add pigment if desired (see below) and whisk thoroughly until well incorporated.
4. Can be used immediately, but will improve if left to stand for 1 hour or more. If it is standing for a day or more, more water may need to be added before use to thin it down to the desired consistency.
5. Whisk thoroughly immediately before use, and continue to stir at intervals throughout the application process.
Amounts and coverage:
6-8 sq. m. per litre. Coverage may vary depending on the texture and porosity of the wall surface.
Limewash with linseed oil
Use when extra water-shedding properties are needed.
N.B. Wear protective clothing and goggles.
Ingredients:
- One 3-gallon (15 litres) bucket of limewash (a standard builder's bucket).
- 2 tablespoons of boiled linseed oil (roughly 3-4%% by volume).
Mixing:
1. Mix a basic limewash.
2. Add linseed oil, (heating the oil gently aids dispersion) and mix in thoroughly. Best used immediately. Mix regularly during application to prevent oil from separating from the limewash.
Amounts and coverage:
5-7 sq. m. per litre. Coverage may vary depending on the texture and porosity of the wall surface.
