What is lime paint?

Lime paint is a breathable wall coating made from slaked lime (calcium hydroxide), water, and natural additives like casein (milk protein) or linseed oil. It hardens by absorbing carbon dioxide from the air, a process called carbonation, gradually turning back into limestone.

Lime paint has been used in the UK for centuries, particularly on heritage buildings, because it allows moisture to move through the wall fabric without trapping damp. Modern lime paints from manufacturers like Cornish Lime, Keim, and Bauwerk contain additives that improve adhesion, opacity, and coverage compared to traditional limewash.

Lime paint is classified as a mineral paint or breathable paint. It has a high pH (alkaline) which gives natural resistance to mould and algae growth.

What is limewash?

Limewash is the original form of lime coating. It's simply slaked lime mixed with water, sometimes with earth pigments added for colour. It's thinner and more translucent than lime paint, soaking into the substrate rather than forming a distinct film on the surface.

Limewash requires 3-5 coats for even coverage. Each coat is applied thinly and allowed to carbonate (usually 24 hours between coats in good weather). The finish has a soft, matte texture and shows natural variation in tone, which many heritage building owners prefer.

SPAB (Society for the Protection of Ancient Buildings) recommends limewash for listed buildings and conservation work because it's the most traditional and reversible finish.

Limewash vs lime paint

Both are breathable and suitable for heritage walls, but they differ in coverage, cost, and application.

Coverage

Limewash is translucent, so you need 3-5 coats to achieve even opacity. Lime paint (with casein or oil additives) is more opaque and typically needs 2-3 coats. Coverage per coat is similar for both (4-6m² per litre depending on substrate porosity).

Cost

Limewash costs £8-15 per litre. Lime paint costs £25-40 per litre. For a 50m² exterior wall, expect to use 10-12 litres for limewash (4 coats) vs 8-10 litres for lime paint (2.5 coats). Total material cost is similar (£100-150), but lime paint saves labour time.

Finish

Limewash has a soft, matte, slightly chalky finish with natural tonal variation. Lime paint has a more uniform, slightly denser finish. Both are matte (no sheen). Limewash ages beautifully, developing a patina over time. Lime paint is more stable in colour.

Durability

Lime paint lasts 5-8 years on exposed walls, 8-12 years on sheltered walls. Limewash needs refreshing every 3-5 years on exposed walls. Both carbonate over time, becoming harder and more durable. Neither flakes or peels like acrylic paint because they bond into the substrate.

Why use lime paint on heritage buildings?

Heritage buildings (pre-1919 solid walls, listed properties, buildings with lime mortar or lime render) need breathable finishes. There are three main reasons for this.

1. Moisture movement

Solid walls (no cavity) absorb rain on the outer face and rely on evaporation to dry out. A breathable paint allows moisture to evaporate through the paint layer. Non-breathable paints (vinyl emulsion, masonry paint with waterproof additives) trap moisture inside the wall, leading to damp, spalling render, and internal wall damage.

Historic England guidance states: "Paint finishes on solid walls should be breathable to avoid trapping moisture." Lime paint has a vapour permeability (SD value) of less than 0.2m, classified as highly breathable under BS 7543.

2. Substrate compatibility

Lime paint bonds chemically with lime-based substrates (lime render, lime plaster, soft brick). It doesn't form a hard film, so it moves with the substrate as the building flexes. Modern masonry paints form a flexible but impermeable layer that can trap moisture and de-bond from soft render over time.

3. Reversibility

Lime paint can be removed (by brushing or washing with water) without damaging the substrate. This is important for listed buildings, where conservation officers require reversible treatments under the Planning (Listed Buildings and Conservation Areas) Act 1990.

Lime paint vs masonry paint

Masonry paint (also called exterior emulsion or weathershield) is a modern, water-resistant coating designed for cavity-wall buildings. It's not suitable for heritage solid-wall buildings.

Breathability

Masonry paint has low vapour permeability (SD value 0.5-2m), meaning it blocks moisture movement. Lime paint is highly breathable (SD less than 0.2m). On a solid wall, masonry paint traps moisture, causing damp and render failure. On a cavity wall, this is less of an issue because moisture drains through the cavity.

Durability

Masonry paint lasts 8-12 years on exterior walls. Lime paint lasts 5-8 years. However, masonry paint can peel or flake if applied to soft lime render, requiring complete stripping and re-coating. Lime paint never peels because it bonds into the substrate.

Cost

Masonry paint costs £8-15 per litre. Lime paint costs £25-40 per litre. For a 50m² wall, masonry paint costs £100-200 in materials. Lime paint costs £250-400. Labour is similar (masonry paint needs 1-2 coats, lime paint needs 2-3 coats).

When to use each

  • Lime paint: pre-1919 solid walls, listed buildings, lime render, lime plaster, soft brick or stone.
  • Masonry paint: modern cavity-wall homes (post-1930s), cement render, hard brick or concrete block.

If you're unsure, check with a SPAB-trained contractor or conservation officer. Using masonry paint on a heritage building can cause expensive damage and may require enforcement action if the building is listed.

What can you paint with lime paint?

Lime paint is suitable for breathable, porous substrates. It will not adhere to non-porous or sealed surfaces.

Suitable substrates

  • Lime render or lime plaster (internal or external).
  • Bare stone (limestone, sandstone, soft brick).
  • Clay plaster or earth walls.
  • Gypsum plaster (if unsealed and porous).
  • Previously painted walls if the existing paint is lime-based or mineral-based.

Unsuitable substrates

  • Vinyl emulsion, acrylic paint, or gloss paint (non-porous).
  • Sealed gypsum plaster or PVA-sealed walls.
  • Cement render (lime paint will adhere but offers no breathability benefit).
  • Wood, metal, or plastic (lime paint needs a mineral substrate to carbonate).

If the wall has been painted with vinyl emulsion, you must strip it back to bare plaster first. Lime paint applied over vinyl will not bond and will powder or wash off.

How to apply lime paint

Lime paint application is different from modern emulsion. It requires a damp substrate and multiple thin coats.

Preparation

Remove any loose or flaking material. Brush down the wall with a stiff brush. If the substrate is dusty, apply a lime water spray (1 part slaked lime to 10 parts water) and allow it to dry. This stabilizes the surface.

Damp the wall 10-15 minutes before painting. Lime paint needs a damp substrate to bond correctly. Spray the wall lightly with water using a garden sprayer or wet it with a brush. The surface should be damp but not dripping.

Mixing

Lime paint is supplied ready-mixed or as a powder to mix with water. Stir thoroughly before use. For the first coat, thin the paint by 10-20% with water to improve penetration. Subsequent coats can be full strength.

Application technique

Apply lime paint with a large brush (100-150mm masonry brush) or a roller. Work in thin coats, using cross-hatching strokes (horizontal, then vertical) to work the paint into the substrate. Don't overload the brush. Lime paint is thinner than emulsion and will drip if applied too thick.

Allow each coat to dry for 24 hours before applying the next coat (longer in cold or damp weather). Damp the wall again before each new coat. Apply 2-3 coats for lime paint, 3-5 coats for limewash.

Curing

Lime paint cures by carbonation, which takes several weeks. Protect freshly painted walls from frost, heavy rain, and strong sun for the first 7 days. If weather is very dry, mist the wall with water daily for the first 3 days to slow drying and prevent powdering.

Coverage calculator

Work out how much lime paint or limewash you need for your wall area.

Maintenance and recoating

Lime paint does not peel or flake, but it will weather over time. Exposed walls (driving rain, coastal, hilltop) may need refreshing every 5-8 years. Sheltered walls can last 8-12 years.

To refresh lime-painted walls, simply apply 1-2 new coats of lime paint over the existing finish. No stripping or sanding is needed. Brush off any loose material, damp the wall, and paint.

Limewash may need refreshing every 3-5 years on exposed walls. Again, no preparation is needed beyond brushing and damping.

Common mistakes

Applying lime paint over vinyl emulsion

Lime paint will not bond to non-porous surfaces. It will powder or wash off. Strip back to bare plaster first, or use a breathable mineral paint designed to bond to sealed surfaces (e.g. Keim Ecosil or Earthborn Claypaint).

Not damping the substrate

Dry walls suck moisture out of lime paint, preventing proper carbonation. The paint will remain soft and powdery. Always damp the wall before painting.

Applying too thick

Lime paint should be applied in thin coats. Thick coats will crack as they dry. If you need more opacity, apply additional coats rather than one thick coat.

Painting in the wrong weather

Avoid painting in frost, heavy rain, or strong sun. Lime paint needs moderate temperatures (5-25°C) and steady drying conditions. If it dries too fast, it will powder. If it freezes before carbonating, it will fail.

Planning permission and listed buildings

If your building is listed, you need listed building consent before painting external walls, even if you're using lime paint. The local planning authority will usually require lime-based paint for heritage masonry.

For buildings in conservation areas (not listed), external painting may require planning permission depending on local authority rules. Check with your council before starting work.

For non-listed, non-conservation-area properties, you can paint without permission. However, if your building is pre-1919 solid wall, lime paint is still recommended to protect the wall fabric and avoid trapped damp.

Cost comparison

For a typical 50m² exterior wall:

  • Limewash: £100-150 materials (10-12 litres, 4 coats). Labour £600-900 (3-4 days). Total £700-1,050.
  • Lime paint: £250-400 materials (8-10 litres, 2.5 coats). Labour £500-800 (2-3 days). Total £750-1,200.
  • Masonry paint: £100-200 materials (8-10 litres, 1.5 coats). Labour £400-600 (2 days). Total £500-800.

Masonry paint is cheaper upfront but unsuitable for heritage buildings. Lime paint costs more but protects the wall and complies with conservation guidance.

Summary

Lime paint and limewash are breathable finishes for heritage walls. Limewash is cheaper but needs more coats. Lime paint has better coverage and durability. Both allow moisture to evaporate, protecting solid-wall buildings from trapped damp.

Use lime paint on pre-1919 solid walls, listed buildings, lime render, and lime plaster. Do not use masonry paint on heritage buildings. It traps moisture and is not reversible.

Apply lime paint in thin coats on a damp substrate. Allow 24 hours between coats. Protect from frost and heavy rain for the first week. Refresh every 5-8 years on exposed walls.