kalkmortels

Kalkmortels are lime-based mortars used in masonry and plaster, with lime acting as the binding agent. In Dutch usage, kalkmortels refers to mortars that rely on lime binders rather than cement. They have a long history in Europe and remain common in the restoration of historic buildings because of their compatibility with traditional masonry materials.

Typical kalkmortels consist of a lime binder (lime putty or hydraulic lime) and an aggregate such as sand. Lime putty mortars use non-hydraulic lime and cure by carbonation, resulting in high porosity and breathability. Natural hydraulic lime mortars contain hydraulic binders that gain strength through a hydraulic set, enabling earlier strength development. Modern variations may include pozzolanic additives or small amounts of cement to adjust workability and strength, but traditional lime mortars emphasize lime as the primary binder.

Kalkmortels are characterized by their permeability, deformability, and relatively low strength compared with cement mortars. They allow moisture to move through the wall, reducing the risk of trapped moisture and salt damage and helping to preserve historic materials. Their slower cure requires appropriate weather protection during setting, and they are generally softer and more forgiving to substrates than cementitious mortars.

In restoration work, kalkmortels are chosen to match the historical fabric, climate, and building physics. Mix proportions, sand grading, and aggregate type are selected to achieve compatible porosity and mechanical behavior. Repointing and repairs are typically done with compatible lime mortars rather than cement-based alternatives to maintain long-term durability of historic masonry.