Rising damp and salt damp in brick walls: causes and fixes

If the bottom of an internal or external brick wall is tide marked, flaking, or smells musty, you may have rising damp. It is common in older Melbourne homes and it is worth understanding before you spend money on the wrong fix.

What is going on

Rising damp is groundwater drawn up through the brick and mortar by capillary action, like water climbing up a sponge. It carries dissolved salts with it.

• As the water evaporates near the surface, the salts are left in the wall.
• Those salts attract more moisture and break down the brick face and mortar over time.
• That salt driven damage is what people often call salt damp.

You usually see it as a band low on the wall, with white salty deposits, bubbling paint, or crumbling render.

Why it happens

Most rising damp in older homes comes down to a few causes.

• No damp proof course, or an old one that has broken down over the years.
• Garden beds, paths, or concrete built up above the original damp course level.
• Poor drainage and subfloor ventilation keeping the base of the wall wet.

Melbourne's clay soils holding winter moisture against the footings do not help.

How it gets fixed

The right fix depends on the cause, and honest diagnosis comes first.

• Lower external ground and paving back below the damp course so water is not bridging it.
• Improve drainage and subfloor airflow so the base of the wall can dry.
• Install or reinstate a damp proof course where there is none or it has failed.
• Replace badly salt damaged bricks and render once the moisture source is dealt with.

What does not work is sealing or painting over it and hoping. Trapped moisture just moves along and comes back worse. If you have a damp band low on a wall, send a photo and your suburb and we will help you work out the cause before anything gets patched.