Mold Under the Sink and Mold from Plumbing Leaks

North Bay Mold Remediation connects Marin and Sonoma property owners with local mold remediation contractors who clean up mold from plumbing leaks and dry out the cabinets, walls, and floors behind them.

Why slow leaks cause more mold than big ones

A burst pipe gets noticed in minutes. A drip from a loose P-trap, a worn supply hose, or a cracked drain line can run for months inside a closed cabinet or wall. The EPA says water-damaged materials should be dried within 24 to 48 hours to prevent mold growth. A slow leak never gives them that chance. By the time you see a stain or smell something musty, the particleboard cabinet floor, the drywall behind it, and sometimes the subfloor have been wet for a long time.

The usual sources

• Kitchen and bathroom sinks. Drain fittings, supply lines, and garbage disposals under the sink.
• Dishwashers. Supply and drain connections and door gaskets, with water running under the unit into the subfloor.
• Refrigerator ice makers. Small supply lines behind the fridge that leak where nobody looks.
• Toilets. A failing wax ring or supply line wets the floor around and beneath the toilet. See bathroom mold removal.
• Water heaters. Leaks from the tank, fittings, or relief valve line, often in a garage, closet, or crawl space.
• Washing machines. Hoses and drain standpipes.
• Supply and drain lines in walls and under floors. In older homes, original piping can corrode or crack with age. In raised-floor homes, a leak under the house may go unseen until the crawl space smells. See crawl space mold.

Plumber first, then mold cleanup

If water is still leaking, shut off the fixture's supply valve or the main, and get the leak repaired. Plumbing work in California falls under the CSLB C-36 Plumbing classification, and any job of $1,000 or more in labor and materials requires a CSLB license. Once the leak is fixed, the mold side of the job can begin:

• Moisture meter readings to find how far the water traveled into cabinets, walls, and subfloor
• Containment around the work area, with HEPA air filtration for larger jobs
• Removal of moldy particleboard, drywall, insulation, and flooring that can't be cleaned
• Cleaning and drying of framing and subfloor with dehumidifiers and air movers
• A check, ideally independent, before new cabinets, drywall, or flooring go in. See clearance testing.

Some contractors handle both the drying and the rebuild; others leave rebuild to a separate contractor. Ask which you are getting. If the job involves cutting drywall, texture, or old sheet flooring in a home built before 1980, ask about asbestos testing first. Asbestos work needs CSLB asbestos certification or a C-22 license plus DOSH registration. Check any license at cslb.ca.gov.

Older plumbing in the North Bay

Roughly 56 percent of Marin homes were built before 1970. Many have had their plumbing updated, but original fixtures, water heaters tucked into closets and crawl spaces, and decades-old drain lines are still around. Whether the house is a mid-century ranch in San Rafael or Novato, an older home in Petaluma, or a newer subdivision in Rohnert Park, the pattern is the same: a slow leak under a sink, a slab, or a raised floor stays hidden until it shows up as a stain or a smell. If a leak turned into a larger flood, see mold after water damage.

What to do before the contractor arrives

• Stop the water and empty the cabinet
• Photograph the damage and the leak for your records or an insurance claim
• Leave cabinet doors open and run a fan or dehumidifier, but don't scrub large areas of growth or start tearing out drywall
• Note when you first noticed the leak; it helps with drying and with any claim

Found mold under a sink or behind an appliance? Call (415) 234-5586 or request an estimate and we'll connect you with a local mold remediation contractor.