Although there are a number of different defects that can cause brick mortar joints to fall out, if only the horizontal mortar joints are dropping and not every horizontal joint is having the problem, it is likely due to corrosion of brick “ladder” wire reinforcement. It’s called ladder reinforcement because the simplest version resembles a ladder, like in the photo below, although other designs have diagonal wires or mesh. Embedded ladder wire reinforcement in the mortar joint strengthens the wall in the same way that steel bars reinforce concrete.

    Ladder reinforcement is offered in varying levels of corrosion resistance, starting with stainless steel and heading downward to basic galvanized. When corrosion begins—and corrosion of steel is a slow, but powerfully expansive process—the rusted steel gradually pushes out the mortar. Because the ladders are typically installed several courses apart, one of the ways to recognize this defect is that the distress occurs only on specific horizontal courses spaced equally apart, like in the photo below, of an entry wall at a residential development.

    If the ladder corrosion is advanced, you can easily see the corroded steel wires in the strips of missing mortar.

    In the early stages, the mortar is still in place but slightly pushed out. 

    Because moisture accelerates the corrosion, once the joint begins to open and lets rain water in, the process speeds up. A similar defect in concrete, caused by rust of reinforcing steel bars, is called spalling. To learn about concrete spalling, see our blog “There’s cracks running along the home’s concrete tie beam. What’s wrong?”

    If the lines of mortar that have fallen out are randomly spaced and other areas of mortar joint are simply deteriorated, then the problem is due to age or minor settling of the wall, and the mortar needs to be repointed.

• • • • • • • • • • • • • • • • • • • • • • • • • • • • 

To learn more about exterior walls and structures, see these other blog posts:

• What is the average lifespan of a house foundation?

• What causes vertical cracks in fiber cement siding planks?

• What causes raised white lines of residue on a block wall that are crusty and crumbling? 

• What is the difference between soil subsidence, heave, creep, and settlement? 

• How much ventilation is required for the under-floor crawl space of a home? 

• How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?

• What causes the surface of old bricks to erode away into sandy powder? 

• What are the pros and cons of concrete block versus wood frame construction?

• Should I buy a house with a crawl space? 

• Why is my stucco cracking?

• How do I recognize serious structural problems in a house?

• What causes stair-step cracks in a block or brick wall?

• What causes a horizontal crack in a block or brick wall? 

• What is engineered wood siding?

• Should I buy a house that has had foundation repair? 

• What is a "continuous load path”?

• How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

        Visit our EXTERIOR WALLS AND STRUCTURE page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.