Pre-Purchase Rising Damp & Waterproofing Inspections
Aluminium Dampcourse Corrosion
How Aluminium (Alcor) Dampcourses Break Down
Aluminium is a lightweight, corrosion-resistant metal, and when it’s coated in bitumen (as in Alcor dampcourse), it does a good job of blocking rising damp. The bitumen acts as a waterproof shield, protecting the metal from moisture and salts inside the wall.
But over time—or during construction—scratches, cuts, or rough brick surfaces can expose small areas of bare aluminium. Once that happens, the exposed metal can start reacting with moisture and salts drawn up by rising damp.
The main problem again is chloride from dissolved salts (sodium chloride). In damp masonry, those chloride ions can reach the exposed aluminium and start a slow corrosion process.
Here’s what happens step by step:
Exposure: The bitumen layer is damaged, revealing bare aluminium.
Moisture and Chloride Contact: Rising damp water brings chloride ions (Cl⁻) into contact with the metal.
Reaction: The aluminium reacts with oxygen and moisture, forming aluminium hydroxide (Al(OH)₃).
Acceleration by Chloride: Chloride ions dissolve this protective layer, allowing oxygen and water to reach deeper into the metal.
Result: The corrosion continues, forming aluminium oxide (Al₂O₃)—a white, chalky residue. This weakens the dampcourse and can let moisture pass through more easily.
While aluminium oxide normally forms a protective film, in damp, salty conditions it becomes porous and flaky instead. Over years, this can compromise the barrier, especially near mortar joints or cuts made during installation.
A damaged Alcor dampcourse often shows white chalky corrosion marks or small pits on the metal surface—early signs that the barrier is breaking down.
Aluminium Dampcourse Corrosion Process
Hydration Shell Illustration
Aluminium has long been used in old buildings as a barrier to stop moisture from rising up through walls. It’s a durable metal—normally lasting for generations. But even aluminium can slowly corrode when exposed to the right mix of moisture and salts from the ground.
When moisture rises through brick or mortar, it often carries dissolved salts with it—mostly sodium chloride (ordinary salt). Once salt mixes with water, it separates into sodium (Na⁺) and chloride (Cl⁻) ions. Each ion becomes surrounded by a small shell of water molecules—this is called a hydration shell.
The sodium ion is relatively harmless, but the chloride ion can trigger corrosion. In damp conditions, chloride doesn’t attack aluminium directly—it interferes with the protective layer that normally forms on the surface of the metal.
Treating your rising damp with our injection products can repel water from your building’s masonry
