Cracks, Hollow Plaster and Peeling PaiCracks, Hollow Plaster and Peeling Paint: Why Wall Finishes Fail and How to Fix Them Properlynt: Why Wall Finishes Fail and How to Fix Them Properly

Wall defects get repaired the same way in most buildings: fill, sand, repaint. That works when the defect is only cosmetic. When it is not, the crack or patch returns, often within months, because the cause was never touched.

Reading the crack

•     Fine hairline cracks are often shrinkage in plaster or paint and are usually cosmetic.

•     Cracks at junctions between different materials, such as block and concrete, usually come from movement and need proper reinforcement, not just filler.

•     Wide, stepped or growing cracks can indicate structural movement. These need assessment by a qualified engineer before any cosmetic repair.

Hollow plaster

Tap the wall lightly. A hollow sound means the plaster has lost its bond with the wall behind it. Causes include moisture, a dirty or poorly prepared surface, or plaster applied too thickly in one pass. Hollow plaster must be cut back and redone. Painting over it hides the problem until the plaster falls.

White salts and bubbling paint

White powdery deposits on a wall, called efflorescence, are salts carried to the surface by moisture moving through the masonry. They are a sign of a water source that needs to be found. Paint applied over them will blister again. See our post on when repainting is a maintenance issue.

A repair sequence that lasts

•     Identify and stop the cause, whether that is a leak, a drainage problem or movement.

•     Cut out loose or hollow plaster back to sound material.

•     Repair with a suitable bonding agent and mesh across junctions where movement is likely.

•     Allow proper curing time before priming.

•     Apply the correct primer and finish coats in suitable conditions.

When to call for an assessment

Cracks that are wide, growing, or running across several floors, and doors or windows that suddenly stick, should be assessed before any repainting is planned.

Not sure whether a wall defect is cosmetic? Book a free surface assessment. Our painting works team will check the cause before any paint goes on.