12/15/2025
Those red/brown, mushroom-like bumps sometimes seen on cast-iron drain piping are called tubercles. They are corrosion deposits that typically form as the pipe reacts with moisture over time, often starting from the inside of the pipe.
Tubercles are most commonly caused by long-term exposure to moisture and the natural aging of cast-iron plumbing materials.
Typical remediation depends on the condition of the pipe and may range from continued monitoring, localized repairs, interior pipe lining, or full replacement when the piping reaches the end of its service life