Breathable Paint for Interior Walls & Lime Plaster
Breathable paints are designed to allow moisture or water vapour to pass through the surface, rather than trapping it inside your walls. In homes where damp is present, particularly solid wall traditionally built properties, breathability is essential. It allows moisture a clear route to escape, avoiding damage to walls and paint finish.
You'll see plenty of products labelled as breathable paint, but the term is often used loosely confusing customers. True breathability is measured by SD value, the lower the number the easier it is for moisture vapour to pass through the paint.
When damp prone walls are painted with conventional paints the moisture can build up behind the paint (due to most paint being made from plastic) which eventually destroys the plaster, which can cause no end of issues. Damp walls cause mould and mildew, which using breathable paint can help avoid.
Breathable paint for lime plaster: If painting over lime plaster, Auro 344 is ideal as it is a lime based paint, although Auro 555 is compatible if you want colours. Bare plaster? Use this plaster primer.
How is paint breathability measured?
Fundamentally, breathability is measured using an SD value, which is known also as “equivalent air layer thickness”. The lower the SD value, the more permeable the paint is for water vapour to have the ability to pass through. This is a good thing, we want moisture to be able to exit the walls (through the paint), as this stops mould and mildew growth.
Does breathable paint prevent mould?
Yes, breathable paint helps prevent mould by letting moisture evaporate through the paint layer. This reduces the presence of damp, which is a key driver of mould growth. Lime based paints are particularly effective due to high breathability and naturally alkaline ph which provides natural mould resistance.
Are clay paints breathable?
Clay paints are also very breathable and a common choice.
What is a good SD value?
Anything below 0.5 is great, and more than enough for most homes. This 0.5 Sd value means that the paint “has the same vapour resistance of 0.5 metres of still air”. SD values are put into classes, and SD Class 1 shows the highest level of breathability (SD value of less than 0.14m)
SD Classes of Breathability
SD Class 1 - Highly Breathable - 0 to 0.14m
SD Class 2 - Moderately Breathable - 0.14 to 0.5m
SD Class 3 - Limited Breathablity - 0.5 to 1.5m
SD Class 4 - Low Breathability - 1.5m+