Limewash is a matt water based paint suitable for both interior and exterior use.
Limewash is also one of the planet's cheapest paints.
There are many lime based paint formulae, and naming is inconsistent. Searching will turn up other paints described as limewash, often these are what is best known as whitewash, which is a significantly different paint (usually chalk & glue - but again, other whitewash formulae exist).
Limewash is made from lime putty, just dilute the putty 50/50 with water.
Lime putty can either be bought or made from bagged lime.
From Bagged Lime
Take bagged lime from any builders merchant, B&Q etc, (this is hydrated non-hydraulic lime) and mix with water to form a putty. Leaving the putty in a sealed container or under water for a couple of days is optional, some say it improves the texture.
Dilute it 50/50 to make limewash.
Dilute the putty 50/50 with water. You now have limewash.
I've nearly always had good results with 2 coats. If you get the mix too thin it would take more, but this is easy to correct on the 2nd coat.
Some people prefer a thinner mix than 50/50. Thinner mixes can give a better final finish quality, but increase the number of coats needed.
On horizontal exterior surfaces it is possible to use just 1 coat. A fairly thick layer of the thin paint is spread on and not brushed out. (Don't thicken the paint, that causes cracking.) This has been enough to make bare grey concrete a good full bodied white.
For interior use its best to use 3 coats of slightly thinner paint in order to avoid slightly raised brush marks.
Sometimes limewash won't stick as well to concrete, gypsum, and some other surfaces, sometimes its fine. If a surface is encountered that it doesn't stick to, the addition of 0.5% to 0.75% boiled linseed oil to the paint makes it stick more.
It doesn't rub off onto clothes in normal use. Brushing against it daily is not a problem. Only if you scrape it hard would a little dust come off, so its no good for hard wear areas.
When first applied, limewash is powdery and physically very weak. It takes a day or 2 to harden up, and longer to reach peak strength. In very cold weather this may take longer.
When first applied the paint looks excessively thin. Don't worry about this, it bodies up when it dries, then it bodies up again when it cures. First time users are tempted to thicken the paint or apply it more thickly; don't, this would cause cracking.
Stir it up frequently during painting, as it tends to settle quite quickly. It is thus recommended to paint from a small container so that stirring only takes a moment. I stir about every 3rd brushful, otherwise it settles out.
Leave the first coat a day before applying the second. If you apply the 2nd as soon as the first is dry, the first coat would come off. This is because curing takes longer than drying, the paint is not cured as soon as its dry.
Uncured paint is basically damp powder. This gradually chemically reacts with CO2 in the air to form a hard layer of paint.
Very absorbent surfaces should be dampened before application.
The liquid paint is thin and ungelled, so is prone to dripping. However limewash has one great property: any freshly dried drops can simply be hosed away. Thus a dustsheet is only wanted where hosing would not be practical. Drops left till next day won't wash off.
Cured paint can be removed with acid if the underlying substance doesn't object.
Exterior painting should not be done when frost is expected. The paint needs to cure before handling frost.
If painting ceilings, a little thickener can help stop drips.
Very powdery lime paint is occasionally seen in neglected spaces in old buildings. This is normally whitewash rather than limewash, typically dating from around the war. Also this level of deterioration is the result of long neglect rather than what would happen in more normal circumstances.
Repainting with limewash
Brush the paint to remove anything loose, dampen if necessary, and repaint.
Repainting with emulsion
Limewash is nearly always used white. It can be coloured if desired, but colouring brings added issues:
- Limewash produces light to medium colours. Dark and saturated colours are much harder to achieve
- Alkali stable pigments should be used. Unstable pigments would fade.
- Limewash lightens during drying & curing
- Mixing a second matching batch is close to impossible, so be certain to make enough coloured paint in one go.
- Weighing the pigment exactly does not ensure identical colour, as grain size affects colour saturation, and grain size is typically not controlled between batches.
Earth gives colours ranging from broken white to brown. Subsoil is most stable. Soil pigments have been used for thousands of years, and are still standard in many parts of the world.
Iron oxide gives pink or an unsaturated red.
Laundry blue gives a light blue, but this is not necessarily alkali stable. The colour may fade in time. This has been used as a colouring agent for interior paints for over a century.
Lime is alkaline, and mildly irritant to skin. Take care not to splash lime into eyes. If this occurs it must be washed out right away, never be tempted to leave it just because it doesn't hurt.
Bagged builder's lime gives a surface finish that is considerably coarser than interior emulsion.
If it takes multiple coats to become full bodied, it went on too thin.
An uncommon method of lime painting can both smooth and paint in one coat. This is usable on concrete surfaces such as exterior walls, where it is desired to improve the rough surface texture.
Instead of diluting the putty, apply it as is using a semi-flexible plastic or rubber edge. Just wipe it on so it fills the indentations.
The result is that the surface roughness is filled to a fair extent, but not completely. Smoothness can not be achieved with one coat because the lime in the indentations shrinks and microcracks as it dries. The result is smoother, but not smooth. When the surface is repainted in several years time, these microcracks are filled and more material is deposited in the hollows, so the surface becomes smoother at each repaint.
A rubber edged grout spreader can be used, but pick one with a stiffer rather than a soft edge, and expect tool wear.
This method uses more lime than standard painting, but its extremely cheap. A £6 bag goes a very long way.
Only one coat is needed to get a full bodied white coat with this method. If you want to apply a 2nd coat for a smoother result, leave the first coat several days to harden first.