Causes of Mold and Mildew

Pests, Wood Rot, Mold and Fungus

The bedroom in the back corner of our basement has a wall that mildews terribly. Previously, I replaced mildew damage near the floor. The entire back of the removed drywall was covered with mildew. Now, mildew is coming through the wall near the ceiling. This wall is the bathroom's toilet wall. There is a half bath on the floor above. Can the condensation of the toilet tanks do this? What other things might contribute to this? What do I need to do to repair this?


Mold/fungus organisms tend to grow on material which is dampened by water leaks and/or condensation. Poor ventilation often contributes to the problem. Mold organisms are unsightly, tend to destroy the infested material, and may be a health hazard. A particular and uncommon strain of mold/fungus, Stachybotrys sp., has received some recent sensational PR (don't believe everything you see on the TV talk shows). Please see, Stachybotrys .

Condensation occurs on surfaces where the temperature is below the dew point of the surrounding air: aluminum window frames, basement walls, bathroom walls and ceilings. The methods used to control condensation include:

  1. Good ventilation, e.g. good quality ducted bathroom fans and whole house mechanical ventilation systems.

  2. Moisture reduction, e.g. dry crawl spaces, fewer indoor plants, a cover on the aquarium.

  3. Insulated surfaces, e.g. insulated window frames, toilet tank covers, insulated walls.

It is quite difficult to get rid of a mold organism which has 'infested' porous material such as wood, plasterboard, wallpaper, etc. While it may be possible to get rid of the mold and mildew on the surface of such materials, some of the mold spores can remain inside the material in a dormant stage, ready to 'bloom' the next time the moisture level reaches 20% or more.

The first step in solving a mold/fungus problem involves changing the conductive conditions which allow for the infestation: water leaks, condensation, and poor ventilation. Any material which has been damaged by the moisture and/or the fungal organism will also have to be removed and replaced with undamaged material. Material which has only been 'stained' by the mold/fungal organism can be cleaned and sealed. For example, stained but undamaged plasterboard can be washed with a household cleaner and then primed with a pigmented shellac and painted. Please see: Restoring and Painting Plaster and Lath Walls. If the drywall has been damaged it should be replaced, preferably with a paperless producrt. George