How to Troubleshoot Mold on Interior Walls


Do you see indoor condensation and the unsightly appearance of mold

        and mildew on your walls? Warm and moist air, inadequate wall insulation,
improper wall construction and lack of ventilation are at the
heart of this issue.

Things You'll Need

  • Foam Gaskets
  • Vapor Retarder
  • Bleach
  • Duct And Vent Materials
  • Exhaust Fan
  • Insulation
  • Caulk And Applicator
  • Timer Control

Exhaust excessive moist air

  • Install an exhaust fan in bathrooms. If you have access from above (an attic), install the fan in the ceiling and vent it out the nearest attic wall. If there is no wall within the limits suggested by the fan's manufacturer, vent the fan through a roof.

  • If you have a bathroom fan, operate it for 20 minutes after showering. Replace the standard switch with a timer control to make this easier (see How to Swap a Faulty Light Switch).

  • Cut down the bathroom door if the gap underneath is much less than 1 inch (2.5 cm). You need that much to provide adequate air for the exhaust fan. See How to Fix a Rubbing Door.

  • Vent clothes dryers to outdoors. You can easily install throughwall kits in most walls. Use rigid aluminum duct, which is easy to cut, assemble and connect.

  • Vent kitchen fans to outdoors and use them whenever you boil water, wash dishes or run the dishwasher.

Tighten a leaky exterior wall

  • Seal switch and receptacle outlets with foam gaskets (energy savers).

  • Caulk joints between floors and walls and around the inside and outside of windows or exterior walls.

  • If there is no vapor retarder (polyethylene sheeting or facing on insulation), make sure there are two coats of good-quality paint on the walls. To see if an exterior wall has a vapor retarder, remove an electrical outlet cover to explore the outside of the box.

  • In bathrooms the problem may be so bad that as a last resort you must remove finished walls to install a proper retarder.

  • Insulate the walls and/or ceilings (see a related problem and the solution in How to Prevent Ice Dams).

Remove existing mold

Tips & Warnings

  • Vapor retarders and sealants prevent moist interior air from penetrating exterior walls on its way to drier outdoor air.
  • The maximum length for an exhaust fan's vent--typically 20 feet (6 m--varies according to fan rating, vent size and type, and other factors.
  • You can adapt some recirculating kitchen-hood fans to vent outdoors.
  • Never use plastic ducts to vent a clothes dryer. Although widely sold for this purpose, they can melt and create a fire hazard.

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