When the term breathability is referred to with reference to building materials it is not concerned with air, but with water in both liquid and gas form. Breathability tends to be used to describe the passage of water vapour and there are a variety of related terms that are used to quantify it.

Water affects everything in building from the health or decay of building fabric, through to the thermal performance of the building and to the health of occupants. Particularly as we try to increase the air-tightness, thermal performance and indoor air quality of our buildings, breathability has become a critical issue, affecting all areas both of new build and of renovation.

Moisture vapour permeability is the ability of a material to allow water vapour to pass through it.  Paints with high water vapour permeability (breathability) enable humidity contained in building structures to be quickly released unhindered into the environment, avoiding moisture build up between coating and substrate. This helps to protect building structures from the damaging effects of build up of moisture.

Breathability also provides an aesthetic advantage as moisture is able to breathe through the coating, rather than being trapped behind an acrylic barrier. If moisture vapour becomes trapped, it will build up behind the coating eventually leading to blistering and flaking of the paint layers, as well as possibly saturated surfaces underneath which often become friable and need repairing.

The micro-crystalline nature of KEIM Mineral Paints creates finite spaces between adjacent crystals; these voids are large enough to allow the free passage of vapour but small enough to prevent the ingress of driven rain. This imparts the KEIM Mineral Paint system with extremely high water vapour permeability. 

TECHNICAL DIGEST - BREATHABILITY & MOISTURE VAPOUR PERMEABILITY - For further technical information regarding breathability and moisture vapour permeability please click on the picture to open the document


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