Kalkkilaasti

Kalkkilaasti, or lime plaster, is a traditional plastering material used on walls and ceilings. It consists of a lime-based binder, usually lime putty or hydraulic lime, combined with sand or other aggregates and water to form a workable plaster. Lime plaster is breathable, flexible, and compatible with historic masonry, helping regulate moisture and temperature.

Two main binder types are used. Lime putty plaster relies on slaked lime and can be mixed with aggregate for interior use; natural hydraulic lime (NHL) or lime with pozzolanic additives provides early strength and improved performance in damp conditions. Modern premixed lime plasters also exist, engineered for consistency.

Application generally follows a multi-coat system. A scratch or brown coat provides the key, followed by a finish coat that can be smooth or textured. Exterior applications may include mesh reinforcement or additional weather protection. Curing occurs by carbonation of the lime with carbon dioxide, and maintaining moisture during the initial days is important, particularly for lime putty plasters.

Advantages include high vapor permeability, adaptability to movement without cracking, and long lifespan when maintained. They are well suited to historic buildings and to sustainable construction. Limitations include slower workability and curing, greater sensitivity to improper moisture handling, and the need for skilled craftsmen. They may not meet early strength requirements in structural applications without hydraulic binders.

In historic or restoration work, kalkkilaasti is commonly used on timber-framed or masonry walls, and repairs are typically done with compatible lime mortars. Finishing with limewash or breathable paints preserves the plaster’s performance and appearance. Safety considerations include tackling lime dust with appropriate PPE.