Mortar Joints – Tooling
Q: What is the purpose of tooling a mortar joint?
A: Tooling has several purposes.
Aesthetically, it produces the joint profile, which is made when the jointer or “tool” is struck against the mortar before the joint has set. This profile is usually concave, but it can have other configurations, such as a grapevine or “v” shape.
Functionally, proper tooling increases the water penetration resistance of the wall. The tool compresses the mortar against the unit, helping seal any slight separation cracks that might form at that interface. The action of jointer on the unset mortar brings the fines to the surface. This creates an exterior skin more resistant to water infiltration.
Timing is key. Too early and the joint won’t seal, too late and it can pull the mortar away. Tooling is done when the joint is “thumbprint” hard. For color consistency, joints should be tooled at the same moisture level.
The sequence of striking must be consistent — head, then bed joints or vice versa. A good BAC craftworker is trained in proper tooling techniques.
Resource: International Masonry Institute – www.imiweb.org