kalkbinder

Kalkbinder is a binding material based on lime, used as mortar, render and plaster in masonry. It is typically derived from lime that has been calcined from limestone or chalk to quicklime (CaO) and then hydrated to slaked lime (Ca(OH)2). In traditional mixtures, carbonation of the lime binder occurs when exposed to air, slowly turning calcium hydroxide into calcium carbonate. Some binders include natural hydraulic lime, which contains impurities such as clay or silica that give the lime a hydraulic set, enabling early strength and workability in damp conditions.

Common forms include lime putty binders, produced by hydrating slaked lime for use with sand in mortars or plasters, and hydraulic lime binders, which rely on pozzolanic components to develop strength without relying solely on carbonation. Lime putty mortars are flexible and breathable but gain strength slowly. Lime binders may be enhanced with pozzolanic additives (e.g., volcanic ash or fly ash) to create pozzolanic or hydraulic mortars. In some contexts, lime binders are mixed with cement to produce lime-cement mortars that achieve higher early strength for restoration work.

Properties of kalkbinders include high breathability, compatibility with historic materials, and flexibility that accommodates movement in old structures. They are favored for conservation and traditional construction because they allow moisture to move and reduce trapped humidity, while being more environmentally friendly than cement-based mortars. Limitations include slower curing, lower early strength, and the need for longer protection against weather during setting. Safety considerations apply when handling lime products, which are caustic until hydrated.