Page title: Breathable Paint

Many products are marketed as ‘breathable’, and whilst all paints are breathable to a degree, what’s important is how breathable. When looking for a Breathable Paint, there are two common ways to check how breathable it is.

The first is the SD (Steam Diffusion) value, which is a German method for measuring breathability. It is widely accepted that for a paint to be classed as breathable it should have an SD value of 1 or lower; the lower the value the more breathable the paint. Earthborn Claypaint has an SD value of just 0.02m.

The other method used to measure breathability is the moisture vapour transmission rate (MVTR). It measures the amount of water vapour (in grams) able to pass through the paint surface over a 24 hour period. The higher the figure, the more water vapour that can pass through, and therefore the more breathable the paint. Earthborn Claypaint has a figure of 1115g/m2/24h, compared with a typical emulsion paint which usually measures between 400-500g/m2/24h.

Many properties suffer from damp, particularly older properties which can be improved with a breathable paint. To resolve this, the approach by some is to seal the building to make it waterproof, using non-breathable building materials and vinyl paints. Whilst this may offer some short-term relief, water will naturally find its way in (through tiny cracks in the walls for example, as the building moves). This water then has nowhere to go, and becomes trapped beneath the waterproof material and paint work, causing damp in the walls.

‘Breathability’ therefore refers to how easily water vapour can pass through a wall. A breathable wall is one that will take in moisture in the air then release it (as if the wall is breathing) without impacting on the fabric of the building. The type of paint you use is one factor that can affect the breathability of the walls.

One way to avoid damp in a building is to use breathable building materials, such as lime render or plaster, followed by a Breathable Paint. Any paints that contain vinyl, acrylic, oils or plastics are not breathable and can trap moisture beneath the surface, causing mould build up or even blowing the paint off entirely.

Even if your property has not been built with breathable materials like lime, using a breathable paint can still contribute to a heathier environment. Claypaint is our most breathable paint, allowing moisture to easily flow through the surface, reducing condensation, mould and mildew.

The SD (Steam Diffusion) value is a German method for measuring breathability. It is widely accepted that for a paint to be classed as breathable it should have an SD value of 1 or lower; the lower the value the more breathable the paint. The SD values for our two most breathable paints have been measured as follows:

Earthborn Claypaint (for interior walls and ceilings) – SD: 0.02m.Earthborn Silicate Masonry Paint (for exterior masonry surfaces) – SD: 0.06m.

The MVTR (Moisture Vapour Transmission Rate) measures the amount of water vapour (in grams) able to pass through the paint surface over a 24 hour period. The higher the figure, the more water vapour that can pass through, and therefore the more breathable the paint. The MVTR values for our two most breathable paints have been measured as follows:

Earthborn Claypaint (for interior walls and ceilings) – MVTR: 1115g/m2/24h.

Earthborn Silicate Masonry Paint (for exterior masonry surfaces) – MVTR: 1264g/m2/24h.

Hygroscopic refers to a substance’s ability to absorb moisture from its surroundings. Being highly breathable, Claypaint is a hygroscopic paint that will ‘even out’ the humidity in a room by absorbing excess moisture. It’s especially suitable for older properties and rooms that have suffered with damp, as it lets the walls breathe. Being hygroscopic, the surface of Claypaint will change and the colour may deepen where it has absorbed moisture. When allowed to dry out naturally these marks should disappear, although in some cases, for example if there are salts in the walls, some staining may occur.

There are a number of causes for damp walls and ceilings. Inappropriate, non-breathable materials are one contributing factor, especially in older properties, along with poor ventilation and poor exterior surfaces like blown brick work. Rooms that are below ground level, such as basements, are also more affected by damp.

We find lots of customers have damp walls which have been coated in non-breathable gypsum plaster and vinyl based paints in an effort to waterproof the room. In the short term this might solve the damp issue by keeping water out, (by, for example, using a damp proof paint) but longer term, moisture becomes trapped under the surface and builds up, so the damp basement walls become more and more saturated.

A better way to treat damp walls is to use breathable building materials such as lime plaster and breathable coatings like limewash or Claypaint. This will allow any moisture trapped within the walls to naturally pass through the surface of the wall and help to regulate the humidity in the space.

Claypaint has an exceptionally high level of breathablilty and is a user-friendly alternative to limewash. It’s available in a wide range of colours with a host of other benefits. Being hygroscopic, the surface of Claypaint will change and the colour may deepen where it has absorbed moisture. When allowed to dry out naturally these marks should disappear, although in some cases, for example if there are salts in the walls, some staining may occur.

We recommend using Earthborn Claypaint on interior lime plaster and lime render because unlike most other paints, it does not reduce the breathability. Conventional vinyl emulsions would partially seal the surface, causing potential problems for the building fabric and the likelihood of the paint ‘blowing off’. Claypaint allows the walls to breathe and offers a viable alternative to lime wash.

A few simple steps should be taken before applying Claypaint to any lime surface:

• Lime render or plaster needs to be fully cured before painting. The best person to advise you is your lime provider, however as a general guide allow at least 1 month curing for every 5mm of thickness. In poor drying conditions this time period may be extended.
• Before painting make sure the surface is stable (not flaky or powdery).
• Slightly moisten the surface before applying the first coat of paint – a water spray bottle is perfect for this.
• When painting onto cured new interior lime plaster, dilute the first coat of Claypaint with around 10% water followed by a full coat.

If over painting interior lime wash, ensure the surface is sound and stable before painting. A diluted coat of Earthborn Wall Glaze may be applied to espcially dusty surfaces to help stabilise prior to painting.

Basements are often affected by damp. We’d recommend Claypaint as a suitable paint for basement and cellar walls with ongoing damp problems. It’s a highly breathable interior emulsion with a high clay content, suitable for painting over new and old lime plaster, as well as painting walls that have been stripped of previous paint, and is an ideal for painting basements.

It’s important to treat the damp problem as a whole. By using a breathable paint in conjunction with other breathable building materials, which will allow moisture and water vapour to flow through the walls and help prevent a build-up of trapped moisture. This is especially important in older properties that may have had a variety of damp proofing works carried out in the past, some of which may not always be suitable for the age of property and original building method. We’d advise contacting a specialist who understands how to treat damp basements and cellars and has experience working with older period properties.

Take a look over on our blog for handy hints and tips.