Lime plaster is a great building material that can help regulate the moisture within a building. Lime plasters prevent damp issues by absorbing and evaporating away any trapped water; the correct paints must be used so this process isn’t stopped. So what are the best paints for lime plaster?
The most important factor to consider is that the paint is breathable. Generally speaking, most natural breathable paints will be suitable for lime plasters. The best paint for lime plaster is limewash or lime paint; these paints contain lime which aids the self-healing process of lime plaster. Other good paints include clay paints (for internal use only) and breathable mineral paints for exterior use. Before using paint on lime plaster, always do a test patch to ensure there are no issues or reactions.
Limewash, Lime Paint and Other Traditional Paints
Confusingly, limewash and lime paint are two different types of paint. Limewash is sometimes called lime paint and vice versa. Both lime paint and limewash are suitable for use on lime plasters. They are both very breathable and, when used correctly, will last for a long time. Limewash and lime paints are VOC-free because they are water-based; they give off no nasty fumes as they cure.
Limewash
Limewash is a traditional type of paint used for thousands of years, going all the way back to Ancient Egypt! It is made from very fine-slaked quicklime, water and various natural pigments. Sometimes other additives are used in limewash, such as casein which helps improve binding, allowing limewash to be used on more surfaces. Small amounts of linseed oil or tallow (animal fat) can also be used in limewash; this helps improve weathering properties.
Related article: Does Lime Plaster Help To Prevent Damp?
Limewash is much thinner than most modern paints and is intended to be built up over many coats. A common guideline is at least 3-4 coats minimum to ensure good coverage and depth of colour. It may be necessary to use more coats; some people have used 10+ coats of limewash. More coats will last longer, provide a deeper, full colour and help iron out any blemishes. Limewash is usually applied with a limewash block brush.
Limewash contains free lime; this free lime can help to fill any small cracks within the plaster, effectively self-healing over time. In exposed conditions, limewash may need a fresh coat yearly. When limewashing is done correctly, using thin coats and allowing 24 hours of curing in between coats, it will not produce a dusty surface. Dusty limewash is caused by poor carbonation, drying too quickly or not preparing the surface properly before painting.
Lime paint
Lime paint is a more modern take on limewash. It is made with similar materials, fine-slaked quicklime, water, pigments and with the addition of acrylic. The addition of acrylic makes lime paints thicker than limewashes; it also helps with curing times and will bind to more surfaces than traditional limewash. Only small amounts of acrylic are used in lime paint, so breathability is not impacted.
Lime paint is a great alternative to limewash as it still contains lime; it is more convenient to use when compared to limewash and helps maintain authenticity. Because it is thicker, you may notice fewer coats are needed. If five coats of limewash are needed, you may only need three coats of lime paint.
Related article: Should Lime Plaster or Render be Sealed?
Lime paint, like limewash, is suitable for internal and external use. Some people may find that lime paint will last longer than limewash, but this is mainly due to the poor application of limewash.
Distemper
Distemper is an extremely old paint. It is usually made from lime, chalk, and water and is bound with animal glue such as casein. Distemper can only be used internally as it can easily wash off the surface. There are three main types of distemper. Soft distemper, which is highly breathable but easily washed off walls, so is generally used in low-traffic areas such as internal ceilings.
Casein and Oil-bound distemper are more hard-wearing. They can be used fairly normally. Oil-bound distemper is the least permeable, and the linseed oil used for this distemper could react with the alkaline lime in plaster, so it’s generally advised it’s not used with lime products.
Soft distemper is an excellent choice for painting ceilings of lime buildings. Limewash and lime paint have much higher amounts of lime. Lime is caustic, so it can cause burns and eye damage, an important factor to consider when painting overhead. Having said that, you should be fine if you wear appropriate protection, such as goggles, gloves and good clothes to cover bare skin.
Clay Paints
Clay paints are a fantastic option for internal painting. They create a beautiful matt finish like limewash, lime paint and distemper. Clay paints are made from water, clay, pigments and sometimes sand or some form of starch. Clay paints aren’t generally suitable for exterior use as the rain will wash them away; the best paint for exterior lime renders are limewashes and mineral paints.
Like all the paints listed here, clay paints are breathable, non-toxic and VOC free. Clay paints such as Earthborn clay paint are washable and better for external use than regular clay paints. They are much thicker than limewashes, and because of this, you may only need one to three coats to achieve a good depth of colour with no blemishes. Clay paints will usually dry in 6-12 hours, so you should be able to apply two coats a day.
Silicate/Mineral Paints
Mineral paints (also known as silicate paints) are the ultimate exterior paint for lime renders. They are made from fine silicate sand, compounds such as potassium carbonate, mineral pigments and mineral filers. Mineral paints are highly breathable while creating an extremely durable finish. Even in extremely exposed areas, these paints can easily last up to and past 15 years, whereas limewash may need a fresh coat yearly.
Mineral paints are durable because they soak into the surface they are painted on, forming a chemical bond with the silica (sand) in the plaster or render. This process is called silicification and bonds deeply with the surface it has been painted onto. Many other paints sit on top of the plaster, which makes it more easily weathered away.
It’s important to note that because mineral paints rely on bonding with the sand in the plaster, any previous paints or finishes must be removed before you use mineral paint. Good mineral paints for use on lime plaster include BEECK Maxil pro, among others.
