The problem is well known: if you pack outer walls too tightly, for example in polystyrene or with impermeable layers of paint, the moisture transfer to the outside is inhibited. In the worst case, the householder no longer gets along with the airing, the water collects in the walls and the molds bloom. Breathable wall paints are an important step in the right direction!
The Sd value provides information on the diffusion openness
The standard DIN EN 1062-1 provides information on the diffusion openness of a paint and thus shows whether the finished coating is really breathable. Pay attention to the so-called Sd value, which indicates the "diffusion-equivalent air layer thickness".
A breathable wall paint can be recognized by a low Sd value, a sealing coating has a high Sd value. For the approximate classification please refer to the following table:
|Sd value||Water vapor permeability||Color class|
|≥ 1.4 m||> 150 g / (m² xd)||low permeability = V3|
|≥ 0.14 + <1.4 m||≤ 150 and> 15 g / (m² xd)||average permeability = V2|
|<0.14 m||> 150 g / (m² xd)||high permeability = V1|
These colors are particularly breathable
Experience has shown that natural paints are among the most breathable paints, including, for example, lime paint, silicate paint and clay paint. Their Sd values are between about 0.02 and 0.05, a healthy indoor climate can greet!
Emulsion paints, as regular wall paints offered in every DIY store, have a Sd value of around 0.5 and are therefore to be arranged in the middle area. Although they do not work like a seal, they can not be described as 100% permeable.
Modern latex paints that no longer contain rubber belong to the emulsion paints and are located in a similar area. Rather, their SD value is slightly higher, depending on the material and ingredients, it may even be almost a V3 color.Tips & TricksBe careful on all aspects of the diffusibility of your walls, for example, do not paint or install any interior insulation. When buying wall paints, the view should always go to the Sd value: This is good for your health!