Breathable Paints Explained

What are Breathable Paints

A breathable paint is one that allows water vapour to travel or permeate through it. Paints with high rates of permeability allow water to evaporate away rapidly while those with a low permeability are likely to trap moisture. These values are measure as an Sd value. An Sd value will measure how much of a barrier the material is to water vapour so therefore a lower figure is more breathable.Typical vapour permeable or breathable paints have an Sd value of around 0.02m to 0.5m.

This would mean that an Sd value of 0.3 is the equivalent to 30cm of air barrier. Non-vapour permeable paint with an Sd value of e.g. 3 is the equivalent of 300cm of an air barrier, making it unable to breathe.

Paints with high Sd values have a detrimental effect on the surface they are applied to as they do not allow it to breathe. Most non breathable paints will not usually disclose their Sd values as they can be much higher than 3. Paints with an Sd value of <0.1 offer adequate breathability to cope with most applications.

Applying Breathable Paints

There is no real difference in using breathable paints to conventional emulsions although we would always advise following the manufacturers’ guidance as each product will differ from the next. Preparation is key and by making sure that the walls are dry, sound and any existing petrochemical paints are removed where possible will help to ensure that your breathable paint acts in the desired way and allows the free movement of any water vapour through your building like a natural dehumidifying system.

Why use Breathable Paints

Damp is commonly found in older buildings. It was believed that the only way to eradicate this issue was to waterproof the entire building or by injecting damp proof courses with the aim to stop water penetrating the building. Whilst this offered a temporary solution it was and is still not the answer, with the majority of these applications ultimately failing.

One of the main reasons for this failure is that a building can undergo significant movement, both structurally and thermally (heat). Once a crack appears water can penetrate the crack and be held within the wall behind the non-breathable or waterproof coating. (Cement renders are also largely impermeable).

A build-up of moisture can lead to damp within the walls which may cause ‘blistering’ and ‘bubbling’ of the paint where the water is trying to escape. In more serious cases the render may be ‘blown’ or forced off by the pressure of the trapped water.

Water that is trapped withina wall can lead to serious deterioration of the building fabric. Any non-breathable paint applied to the building will act like a film around its surface. If you imagine wrapping your walls and ceilings in cling film, this will stop the moisture from going in and out but will trap it and the water will build up within the surface. This is where the term “film-forming” paint comes from as it seals the building and stops the building from breathing and allowing moisture out of the walls.

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Types of Breathable Paints

We offer all types of paints for both internal and external applications. The most commonly known is Limewash which consists of burnt limestone and water. When applied to a porous wall it soaks in, absorbs CO2 and reverts back to limestone. Limewash makes a superb internal and external coating and can be coloured using Pigments.

As a derivative of limewash we also supply Lime Paint which comes in a powder form ready to mix with water. Lime paint can be supplied in 19 different colours and although it contains around 3% acrylic to aid dusting and adhesion it still retains a low Sd value and is highly suited to lime rendered buildings both internal and external.

Mineral Silicate Paints were developed at the end of the 19th century and, as with limewashthe mineral paints soak into the background and bond to it. Where they differ is that limewash generally bonds to the calcium in the background whereas mineral paints form a strong chemical bond with the silica sand in the stone or render.

It is well known what a strong and stable element silica is and it has been widely used in building due to these attributes. This silica bond makes the paints far more durable than limewash or lime paint, leaving the paint attached to the substrate. The way the paint bonds to the surface also gives it extreme durability as the chemical bond achieved means that it cannot be stripped by paint strippers.

Mineral paints also offer much greater longevity compared to limewash and lime paint due to the bond with the surface, they are also non-flammable along with many other benefits depending on what type of mineral paint that is used. They can be mixed to over 300 colours.

Aglaia Natural Breathable Paints are manufactured from plant extracts and contain no VOC’s. These can be applied internally just like a “normal” emulsion paint and are suitable for lime rendered as well as cement rendered walls. Aglaia Breathable Paints are manufactured from only natural ingredients making them environmentally friendly.They use only renewable sources and no petro-chemicals (synthetics), this means they are friendly to people with allergies. Due to their natural makeup they also do not attract dust build up on the surfaces and can be cleaned with water.

We are the principal distributors for Naturepaint which is a breathable powder paint manufactured in Hayle, using locally sourced clay to make the paint. Nature paint contains no VOC’s and is an environmentally friendly paint, picking up many awards including The Observers Ethical Award 2009. We are stockists for Earthborn who supply a range of breathable claypaints and emulsions. Further information including technical data, colour cards and information can be found in our pdf library or by contacting us either by email or telephone.

You may also be interested in our:
Breathable Paints and Decorating Seminar
or our FREE CPD Seminars

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