Mørtel

Mørtel is a binding material used in masonry to hold bricks, stones, and other units in place and to fill joints between them. It serves as both an adhesive and a filler, transmitting loads among masonry elements. Modern mortars are typically cementitious, composed of a binder, fine aggregate, and water; historic mortars often rely on lime-based binders.

Common binder options include Portland cement, hydrated lime, hydraulic lime, or lime-putty. These binders are mixed with aggregates, usually sand, in varying ratios to produce cement mortars, lime mortars, or cement-lime mortars. Typical cement mortars use ratios like 1:3 or 1:4 (binder to sand); lime mortars are commonly 1:2 to 1:3, balancing workability with strength.

Mortar properties depend on the binder. Cement mortars gain strength quickly but are less permeable and less flexible, which can cause cracking in moving or historic masonry. Lime mortars are more elastic and breathable, better matching old structures but slower to gain strength. The choice affects bonding with masonry units, water handling, and durability under freeze‑thaw cycles.

Mortar is used to bed masonry units, fill joints (repointing), and, when used as render or plaster, to finish surfaces. The selection of mortar type is influenced by substrate compatibility, climate, and whether the project involves historic preservation or new construction.

Mortars have been used since ancient times, with lime mortars predominant in traditional European masonry. Portland cement–based mortars became common in the 19th century. International standards for mortars include EN 998-1 and EN 998-2, which define specifications for masonry mortars and lime mortars.