Mortar Matching for Old Kansas City Brick: Why the Wrong Mix Ruins Brick

A lot of older Kansas City homes are built with soft, low-fired brick and a lime-rich mortar. When someone repairs those joints with a hard, modern cement mix, the repair looks fine for a year or two and then the brick starts to flake. The mortar did exactly what it was supposed to do. It was just the wrong job for it.

Mortar is supposed to be the weaker part

Mortar is the sacrificial layer. In a good wall it is a little softer than the brick, so when the wall moves with the seasons, the joint takes the stress and the brick stays intact. Old brick in Brookside, Waldo and the older parts of Kansas City, Kansas is often quite soft. Pair it with a harder mortar and the roles reverse. Water and freeze-thaw stress go to the brick faces, and they spall.

What a good match looks at

• Strength. The new mortar should be the same strength as the original or softer, never harder than the brick.
• Color and sand. Old mortar usually has a distinct tone and grain. A match often uses a custom blend, not one off the shelf.
• Joint profile. Concave, flush, or struck joints each shed water differently. The finished joint should follow the original shape.
• Depth of the cut. Old joints are ground out to a consistent depth before new mortar goes in, so it bonds and does not just sit on the surface.

Signs it was done wrong

If a previously repaired wall has brick faces peeling away next to bright, hard-looking joints, that is the classic pattern. The joint is fine and the brick is paying for it. Our guide on tuckpointing vs repointing vs replacement shows when a wall can be saved and when brick has to come out.

For a wall that needs more than joint work, see our page on brick repair and replacement, or start with the basics on tuckpointing in Kansas City.

Frequently asked questions