A green mouldy looking substance may develop on your copper water pipes, especially at the joint. Typically, this green discolouration is a patina, which develops from plumbers not cleaning away excess soldering flux after joining pipes. Many homeowners mistake the green discolouration for mould. Green can also point to a leak in pipe. Some leaks make their presences known by dripping on the floor while other leaks are very tiny pinholes. Many times pipes will look wet, but that does not necessarily indicate a leak or green mould. Pipes sweat and condensation left on the pipe makes the green area appear wet and mouldy. Finding mould on copper pipes is not typical because copper offers a hostile environment for moulds. Choose the method best suited to your skills and abilities when attempting to remove the green discolouration.
Wipe the pipe with a rag to dry the area and remove condensation.
Rub an emery cloth over the discolouration to remove the green colouring and reveal shiny copper. An emery cloth is an abrasive cloth with a fine grit that is more flexible than sandpaper.
Wet a rag with acetone. Wipe the green section to remove the patina from the copper pipes. Acetone counteracts the patina and restores the copper colouring. Wear eye protection, gloves and a respirator to avoid acetone contact with skin and membranes. Do not use acetone near open flames including pilot lights and lit cigarettes, as it is highly flammable. Clean off acetone residue with a wet soapy rag to avoid combustion. Dry the pipe thoroughly with a rag.
Heat any persistent green sections with the flame from a propane torch. Wipe away melted green soldering flux with a clean rag. Exercise caution when using a propane torch because you can ruin a soldered joint if you apply heat for too long. Wear heat-approved safety glasses and leather gloves when working with a propane torch.
Inspect the pipes closely for signs of leaking water. If the pipe has a leak, the section requires replacement. If you live in an area where the air contains salt, expect your copper pipes to turn green. Keep a fire extinguisher nearby when using a propane torch.
Work in a well-ventilated area when using acetone. Do not use a propane torch near solvents, gasoline or other flammables.