Kalkslak

Kalkslak is a traditional lime-based plaster used in historic masonry, particularly in Northern European architectural contexts. The term is linked to kalk, meaning lime, and a regional word for plaster or putty; the exact etymology varies by dialect.

Composition and preparation: Kalkslak typically consists of lime putty mixed with an aggregate such as sand. Historically, lime putty was produced by slaking quicklime with water, then aged before use. The putty is combined with sand and sometimes other additives to create a workable render for coating walls.

Applications: It is applied in coats to interior and exterior surfaces, often as a scratch coat, brown coat, and finish coat. Kalkslak is valued for its workability, breathability, and compatibility with historic masonry, allowing walls to regulate humidity and moisture.

Performance and maintenance: As a lime-based material, kalkslak sets through carbonation and remains permeable to water vapor. Proper curing conditions are important, and it should not be sealed or topped with cement-based products that block moisture transfer. Damaged areas are typically repaired with compatible lime mortars to maintain continuity and wall physiology.

Historical context: Kalkslak figures prominently in medieval and early modern building practices in Northern Europe. While cement-based plasters became common in the 19th and 20th centuries, kalkslak remains central to restoration and conservation work, where compatibility with original materials is essential.

See also: lime plaster, limewash, breathable masonry, historic preservation.