Which masonry joint design provides the best watertightness?

• A. Vee
• B. Concave
• C. Flush
• D. Weathered

Answer: (B)

Watertightness in masonry depends on how well the mortar joints seal gaps and direct water away from the wall. A concave joint forms a rounded, pressed-in groove that tightens the mortar and creates a self-sealing profile, making it harder for water to penetrate and easier for moisture to be shed along the surface. The curved shape reduces open channels for capillary action and leaves fewer vulnerable edges where water can seep in, so it provides the strongest resistance to water infiltration among common joint types.

A Vee joint, with its sharp notch, can trap moisture in the corners and leaves small gaps that moisture can follow under pressure, making it less watertight. A flush joint is flat with the wall face, which offers less resistance to water movement because any small irregularities can act as pathways for infiltration. A weathered joint relies on sloping surfaces to shed rain, which helps with surface runoff but doesn’t seal as tightly as a concave joint, especially against wind-driven or pressure-driven water.