Why Clay Plaster and Why This Matters

There’s a lot of talk about clay plaster being breathable, but what does that mean?

When people say that clay plaster breathes, they’re usually referring to its vapour permeability—its ability to allow moisture in the form of water vapour to pass through it.

In the world of natural building, you’ll often hear that clay plaster breathes. But what does this really mean, and why is it important?

To “breathe” in this context refers to a material’s vapour permeability—its ability to allow moisture in the form of water vapour to pass through it. Unlike many modern plasters and paints that create sealed surfaces, clay plaster works with the moisture in the air, not against it. This simple property has powerful effects on the health, comfort, and longevity of your home.

Moisture Regulation

Clay is hygroscopic—it naturally absorbs and releases moisture. When the air in your home is humid, the clay will take in some of that excess moisture. When the air becomes dry again, the clay releases it. This ongoing exchange helps to maintain a stable indoor humidity level, which feels more comfortable and reduces strain on heating and cooling systems.

Mould Resistance

Mould thrives in environments where moisture gets trapped. Synthetic wall coatings and impermeable paints can seal moisture into a wall, creating perfect conditions for mould growth. Clay plaster, by contrast, allows moisture to move through and escape, making mould growth much less likely. It’s a passive, chemical-free way to keep your indoor environment healthy.

Comfort and Durability

Because clay plaster helps regulate humidity, it contributes to thermal comfort—you’re less likely to feel that sticky, clammy feeling in summer or dry air irritation in winter. Additionally, by preventing moisture build-up in the wall structure, clay plaster helps preserve the materials underneath, contributing to the long-term durability of the building.

A Living Surface

In a sense, clay plaster is a living surface. It adapts to the environment, constantly balancing moisture levels without mechanical systems or synthetic chemicals. It’s a quiet, invisible kind of intelligence built into the walls.

Choosing Breathable Materials for Healthier Homes

Incorporating breathable materials like clay plaster into your home is part of a broader philosophy of building in harmony with nature. These materials not only create more comfortable and healthier spaces, but they also reduce the need for artificial climate control, making your home more energy-efficient and sustainable.

Whether you’re restoring an old cottage or building a new sustainable home, using clay plasters is a beautiful way to honour natural processes—and breathe new life into your walls.