May 19, 2026 · 5 min read
Natural wall finishes and indoor air quality
People increasingly ask about this, usually because of a nursery, a bedroom, or a household member who reacts to conventional paint.
Why mineral finishes are different
Conventional paint is pigment and binder suspended in a carrier. The binder is usually a synthetic polymer, and both carrier and binder can release volatile organic compounds as they cure and, at lower levels, for a long time afterward.
Lime and clay plasters cure by different chemistry. Lime hardens by reabsorbing carbon dioxide, and clay by drying. Neither relies on a synthetic binder, so there is very little to off-gas.
Humidity buffering
Lime and clay are both porous and hygroscopic, meaning they take up moisture when the air is damp and release it when the air is dry.
In practice that smooths out indoor humidity swings, which is comfortable and also discourages the conditions mold needs. It is one of the quieter reasons old buildings with plaster walls often feel pleasant.
Where microcement sits
Microcement is cement based, so it is mineral rather than plastic in the body of the material, but the sealers used on it vary considerably. If indoor air quality is a priority, ask specifically about the sealer, because that is where the difference lies.
Ask for documentation
Any manufacturer making air quality claims should be able to produce test data for the specific product. Ask for it rather than accepting a general statement about natural materials, and be skeptical of anyone who cannot supply it.
In short
Lime and clay are genuinely low emission by chemistry rather than by reformulation. For microcement, the sealer is the question worth asking.
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