Which mortar joint is most weatherproof?

• A. Flush joint
• B. V-joint
• C. Concave joint
• D. Beaded joint

Answer: (C)

Weatherproofing mortar joints hinges on how the joint is shaped and packed so water is shed rather than drawn into the wall. The concave joint forms an inward-curved profile that is tightly compacted when tooling the mortar. This tight, rounded surface reduces voids and creates a strong seal, which minimizes capillary action and makes it harder for water to penetrate. The curved shape also helps direct any moisture toward the face of the masonry and away from the joint, improving drainage and resistance to freeze-thaw cycles. Because of this combination of compressed mortar and effective water shedding, the concave joint stands out as the most weatherproof choice. In comparison, flush joints can have small voids, V-joints can open up at the point of the V, and beaded joints may trap moisture in the bead, making them less resistant to weathering.