kalkwas

Kalkwas is a traditional lime-based coating used on mineral interiors and exteriors, particularly in historic European buildings. It functions as a breathable protective and decorative layer for lime plaster and other mineral substrates. The coating is typically white or pale, though pigments can be added to achieve various colors.

Etymology and distinctions: The term comes from Dutch, where kalk means lime and was means wash or coating. It is distinct from the German Kalkwasser, which refers to limewater rather than a surface coating. In restoration and traditional building practice, kalkwas is valued for its compatibility with lime plaster and its ability to allow moisture to escape from the wall.

Composition and preparation: Kalkwas is prepared from lime, either lime putty or hydrated lime, mixed with water to form a thin slurry. Pigments such as ochre, sienna, or umber may be added for color. The mixture is applied in thin coats, typically a primer coat followed by one or more finishing coats. The exact ratios and consistency vary by region and desired finish.

Application, performance, and maintenance: The coating is brushed onto a clean, sound surface and allowed to dry slowly. Kalkwas is highly breathable and water-vapor permeable, which helps regulate moisture in old walls but offers limited water resistance. It is susceptible to abrasion and weathering, requiring periodic maintenance and reapplication, especially on exterior surfaces exposed to the elements. It should not be sealed with modern impermeable coatings that trap moisture.

Historical and contemporary use: Kalkwas has been widely used in Northern and Western Europe for centuries and remains common in restoration projects and in eco-friendly new-builds that aim to mimic traditional finishes. See also lime plaster, limewash, and traditional building materials.