Lime plastering
What are the benefits of lime plaster?
Lime plastering has been used for thousands of years in buildings from ancient Roman structures to historic homes across Europe. Made from natural lime, aggregate (can be sand, chalk, hemp, perlite or even earth) and water, lime plaster creates a breathable, flexible finish that works in harmony with traditional building materials such as stone, clay brick and timber.
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Unlike modern gypsum or cement-based plasters, lime plaster allows moisture to evaporate naturally from walls, regulating humidity and reducing the risk of damp and trapped condensation.
Its flexibility means it can accommodate movement in older buildings without cracking. While modern plasters are designed for speed and uniformity, lime plaster offers character, durability, and a softer, more organic finish that improves with age.
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Lime plaster is usually applied with 2 or 3 coats but 1 or even 4 coats may be applied as needed. The process below describes the most common approach.
The lime plastering process
Lime plastering is a very different process to modern plastering. The stages below describe a fairly typical lime plastering job which was completed in December 2025 using a hotlime, perlite and hemp mix on external walls and lime, sand and horsehair on the internal walls, with a clay plaster skim.
Preparing the walls
The first step is to prepare the existing walls, removing damaged or inappropriate materials to make sure a solid, reliable surface is present for the plaster.
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While it is possible to plaster over cement or gypsum, the wall will not be able to breathe with these materials still present. Removing modern plasters is known as 'hacking off' to get 'back to brick' or 'back to stone'.
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If the walls were originally built with laths (wooden strips nailed to studs), the timber should be repaired or replaced with new laths as needed. It is likely that some laths will be damaged during hacking off.
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The substrate must be wetted down before applying lime plaster to slow down the transfer of moisture from the plaster. This transfer is called 'suction'. Too much suction causes the plaster to dry out too quickly, resulting in shrinking and cracking.
The base coat
The first coat of lime plaster is the thick, sturdy base for the rest of the wall, made up of lime, aggregate, and fibres. The aggregate is often sand but many other materials, such as perlite, hemp, clay or even earth can be used. Horse hair is traditionally used for the fibre and that is our preference due to its strength, sustainability and availability. Other fibres such as hemp can be used instead of or alongside horse hair.
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The base coat is applied at 10-12mm thick directly onto the substrate using a hawk and trowel and flattened with a plasterer's darby or other straight edge. This flattening process is called 'ruling off'.
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Once the base coat is on the wall and has been ruled off, it is scratched in a diamond pattern or 'torn' by drawing the trowel across at a wide angle. This provides a 'key' to allow the next coat to stick properly. If the base coat is left smooth, the next coat w not adhere and may detach. The base coat will be ready for the next coat after 1-2 weeks.
The float coat
The second coat, called a float coat, is needed when it's not possible to completely flatten the base coat or if the thickness of the wall needs to be built out. Most pre-1920s solid-walled homes did not have a second coat of lime plaster, instead having a skim straight over the base coat. The Victorians usually only applied three coats to the higher-status homes of the upper classes.
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The float coat plaster is usually the same mix and depth as the base coat but without fibres, and is applied in the same way but finished slightly differently. It is flattened and compressed with a sponge and a wooden trowel known as a float, and then scratched lightly with a 'devil float', a plastering trowel with nails protruding slightly through the flat side which lightly scratches the surface. This provides the key for the following final coat. As with the base coat, it will take 1-2 weeks for the float coat to be ready for the next coat.
The skim coat
The last step is to 'skim' over the wall, providing a flat, smooth finish. This coat is quite different to the base and float coats: the ratio of lime to aggregate is 1:2 or even 1:1 and fine sand is used instead of coarse sharp sand. The thickness of this coat is only 1-2mm.
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Alternatively, clay plaster or pure lime putty can be used instead of the lime and sand skim. A clay plaster skim is slightly smoother than lime and sand but just as breathable, while pure lime putty produces a very smooth, polished surface.
Lime and fine sand produces a textured, light sand coloured finish unless intentionally worked to a polish. It is also possible to add different aggregates such as marble dust to produce even finer finishes.
Aftercare
Depending on temperature and humidity, the wall will be ready for finishing with limewash or distemper after about two weeks. Applying a finish too soon can result in patchiness or flaking so it is a good idea to leave it for as long as possible.
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While many paint companies claim to produce 'breathable' emulsion paints, we do not recommend using anything other than limewash or distemper which are both proven to be vapour and water permeable.
