23 March 2026
Look along a long brick wall and you will often see a straight vertical gap running top to bottom, usually filled with a flexible sealant rather than mortar. That is a control joint, sometimes called an articulation joint, and it is one of the reasons the wall is not cracking.
Brick walls are not as rigid as they look. They expand and contract with temperature and moisture, and the ground underneath moves too. In Melbourne that ground movement is a real factor because much of the city sits on reactive clay soils that swell when wet and shrink when dry. A long, solid run of brickwork with nowhere to give will eventually crack somewhere, usually in an ugly stepped line through the bricks and mortar.
A control joint is a deliberate vertical break built into the wall at planned spacing. Instead of fighting the movement, it gives the wall a place to flex.
Done properly the joint is tidy and intentional. It is meant to be there, and it is far better than a crack you did not choose.
The right spacing and location depend on the wall, the soil and the design, which is why this is set out as part of the build rather than guessed. As a general rule you tend to see them:
Leave the joints out, or space them badly, and the wall does the dividing itself. The result is stepped cracking, joints that open up, and sometimes movement you can feel. Trying to patch those cracks with mortar rarely holds, because the underlying movement is still happening and the mortar is rigid. The proper fix often means cutting in the joint that should have been there.
Not every crack is serious, but stepped cracking along a brick wall is worth understanding rather than just filling. Sometimes it points to a missing or failed joint, sometimes to footing or drainage movement underneath.
If you have cracking you are unsure about, send us a photo of the wall and your suburb and we will give you an honest read on what is causing it.