Old Canaan Building Materials

The mortar joint in a brick wall is usually the last thing anyone specifies carefully and the first thing that fails. The profile of the joint — flush, struck, rodded, raked — determines how water sheds from the wall face. The color of the mortar determines how the wall reads from the street. The width of the joint determines the scale of the coursing. These are not incidental details. They are the face of the wall.

A rodded joint — concave, formed by drawing a rounded tool across the fresh mortar — reads as traditional and is the most common joint on American brick construction from the 19th century onward. It sheds water reasonably well and compresses the mortar surface for better weather resistance. A raked joint — mortar raked back from the face — is a contemporary choice that looks dramatic and is wrong for any exterior application: it collects water, accelerates freeze-thaw damage, and reads as designed rather than built.

Joint profiles are formed by the mason after the mortar has begun to set but before it has hardened fully — a window of one to three hours depending on temperature and mortar mix. Width is determined by the brick dimension and the coursing: standard American brick with a 3/8" joint courses at 2-5/8" per course (2-1/4" brick plus 3/8" joint). The 3/8" joint is the standard.

The joint profile affects water management at the wall face. A concave or rodded joint sheds water most effectively. A struck joint also sheds water. A raked joint traps water on the ledge created by raking. In a New England frost environment, trapped water in a raked joint freezes, expands, and eventually damages both the joint and the face of the brick adjacent to it.

The joint profile, the mortar color, and the joint width together define the visual character of a brick wall as much as the brick itself does. A historically correct brick in an incorrect joint reads wrong. On a traditional building, the mortar joint should be specified as carefully as any other finish material.

Specify joint profile, mortar color, and joint width explicitly in the masonry specification. Mortar can be tinted to match existing or to achieve a desired color relationship with the brick. A light mortar with dark brick reads as a grid. A mortar that closely matches the brick reads as a monolithic wall.