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Natural pigments can be added to lime wash, but first check if they are compatible, as lime is a strong alkali. Pigments in powder form are best mixed with hot water to aid dispersal. The amount of pigment needed depends on the required intensity of color, with a ratio of 20:1 an average figure. With some earth pigments, it is best to soak them for 24 hours first (check manufacturer's instructions).
Add powdered pigment to a jug of hot water (image 1). Using a hand whisk, mix the liquid to disperse the pigment. Add more of the same or different-colored pigments to alter or intensify color (image 2).
Use a trowel to make sure the pre-mixed lime putty is sufficiently mixed (image 1). Aim for a thick, creamy consistency. Transfer three trowel-fulls of the lime putty to a clean bucket (image 2).
Add water slowly to the lime putty. The ratio of water to putty may be 50:50, or even greater depending on its original consistency (image 1). Mix the lime putty and water with a stirring paddle until the mixture is thin and creamy in consistency (image 2). You may add flaxseed oil, especially if the limewash is for exterior use (the oil aids adhesion and durability). As a guide, use a ratio of 12:1 (image 3).
Pour the mixture through a sieve and into a second bucket (image 1). Add any colored pigment at this stage, again mixing it together with a stirring paddle (image 2).
Mix the lime wash again (image 1). It should have a thinner consistency (ideally milk-like) because of the dilution with the pigment. Give the lime wash a final sieve and stir (image 2).
Lime wash is applied in much the same way as most emulsion or water-based paints. It is important to keep a wet edge as the finish can become patchy where overlaps have occurred. Unlike conventional paints, lime wash is always applied to a dampened surface (use a small hand-pumped spray) rather than directly to a dry substrate. It should not be applied in very cold, hot or wet conditions. It is also essential to wear protective gloves and goggles.
Excerpted from Do It Yourself Home Improvement
© Dorling Kindersley Limited 2009