Water Damage to Brick Walls: How to Identify and Treat It

Brick is porous, so it soaks up moisture like a sponge. The first signs are often white, chalky deposits called efflorescence, which appear when water evaporates and leaves salts behind. You may also notice darker, damp-looking patches that never seem to dry, especially after rain.

Check the mortar between bricks. If it crumbles easily or has gaps, water is getting in. Look for moss or algae on the surface, which thrive in damp conditions. A musty smell near the wall can indicate trapped moisture, even if the brick looks dry on the outside.

• White powder or crust on brick faces
• Dark, blotchy stains that stay wet
• Crumbling or missing mortar joints
• Soft or spalling brick surfaces
• Musty odor or visible mold nearby

For light efflorescence, brush the salts off with a stiff nylon brush. Avoid wire brushes or acids, which can damage the brick. Rinse the wall with water and let it dry completely. If the salts return, the moisture problem is ongoing, so repeat the source check.

After the brick is dry, apply a breathable, water-repellent sealer designed for masonry. This lets moisture escape while blocking rain. Do not use paint or a non-breathable coating, which traps water and causes spalling. For stubborn stains or large areas, consider professional cleaning.

• Use a nylon brush, not metal
• Rinse with clean water, no detergents
• Let the wall dry for several days
• Apply a breathable masonry sealer
• Avoid paint or plastic-based coatings

Moisture in brick can lead to mold on the surface or inside the wall. If you see mold, limit your exposure. Wear gloves and a mask while cleaning small areas with soap and water. If the mold covers more than a few square feet or returns, bring in a mold professional to handle it safely.

Stains from water, like rust or tannin, are harder to remove. A poultice of absorbent clay can pull stains out of the brick. For persistent discoloration, the pros may use specialized techniques. If the damage reaches interior walls or ceilings, you might need drywall repair, but focus on the brick first.