Why is breathability so important when choosing paint?

What is breathability?

The term ‘breathability’ can be a bit confusing, especially when it comes to choosing the right paint. When we talk about paint breathability, we’re referring to how much air and water vapour can easily flow through the surface. Using paint with a high level of breathability, coupled with breathable building materials, means that moisture doesn’t become ‘trapped’ beneath the surface of the paint. Trapped moisture, also known as damp, can cause the paint to bubble, peel and eventually blow completely. It can also lead to much bigger problems within the fabric of the building itself.

Whilst one common approach is to use waterproof paints and materials designed to block moisture, this can actually exacerbate the problem. As walls naturally move, tiny cracks appear and let moisture in. Water will often find its way through the smallest of hairline cracks, but with a waterproof paint it remains trapped within the walls, creating damp issues.

How do I know if a paint is breathable?

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. Our 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. Claypaint has a figure of 1115g/m²/24h, compared with a typical emulsion paint which usually measures between 400-500g/m²/24h.

Externally, our  Silicate Masonry Paint carries a reading of 1264g/m²/24h. Most modern masonry paints typically measure between 200-400g/m²/24h and contain non-breathable plastics that, whilst designed to waterproof the building, will flake off in the long run as damp forms.

If you’re unsure as to whether Earthborn’s paints are right for your project, head to our FAQs here or give our team a call on 01928 734171.