What is expansion joint, and why is it required in plastered walls?

• A. A joint introduced at intervals to accommodate movement and prevent uncontrolled cracking
• B. A decorative groove for aesthetics
• C. A joint used to install electrical wiring
• D. A joint used to ventilate moisture

Answer: (A)

Expansion joints are deliberate gaps placed in plastered walls to let sections move independently. Buildings expand and contract with temperature and humidity, and they can settle or shift over time. Plaster on lath or over masonry is fairly rigid, so when the substrate moves, the plaster layer needs somewhere to give. If there’s no expansion joint, the added stress shows up as cracks or even sections pulling away.

In plastering practice, these joints are placed at intervals, and at changes in plane or where different materials meet, such as around openings or at long walls, so movement can occur without cracking the finish. The gap is filled with a flexible material (often backed by a compressible filler) and sealant, which allows movement while keeping water and debris out. This way the plaster stays intact and durable despite the inevitable movement of the building.