Mold and Mildew

There are several kinds of mildew, some are molds and some are fungi. Others are algae, rusts, yeasts, and bacteria. Mildew found on outdoor plants can be powdery mildew, which attacks roses, or downy mildew, which attacks grape vines, cantaloupes, potatoes, and tobacco, among other crops.

But the mildew we’re talking about is that black stuff that sometimes shows up inside our houses. These are molds. But what they have in common with their outdoor relatives is that they thrive only in certain conditions. To wit, they need moisture and certain temperatures to grow on many types of surfaces, from plant leaves to stored garments. In the home, mildew develops on damp cotton, linen, rayon, silk, wool, leather, wood, and paper. Many synthetic fibers resist it. It commonly develops in humid summer weather, especially in houses that are closed.

Another thing all mildew needs to flourish is darkness and dampness; it also prefers places where fresh air is not circulated. So cellars, crawl spaces, and closets are ideal areas for it, as are air conditioning ducts.

How to Prevent Mildew

At high risk are draperies and rugs in basements, shower curtains and bathtub caulk in bathrooms, and damp clothes rolled up for ironing. The stuff leaves a musty odor and discolors fabrics. Sometimes it eats so deeply into fabric that the item rots and falls to pieces. It discolors leather and paper. It is a hazard to stored goods and is of particular danger to valuable museum collections. Staining and deterioration of fabric, paper, and leather caused by mildew is irreversible.

To keep mildew at bay, deny spores the moisture necessary for germination by controlling the humidity inside your house, preferably keeping it between 45% and 55%, and no higher than 65%. You may need to install dehumidifiers. Also keep air circulating, with fans, if necessary, and try to maintain a temperature between 64 degrees F to 68 degrees F, plus or minus five degrees. Repair leaking pipes, gutters and downspouts, cracked windows, a problem roof, deteriorated masonry, and cracked walls. Cleanliness of the environment is also important, as organic debris nourish spores.

Cleaning Mildew from Surfaces

When storing materials, packing such buffers as silica gel with the goods before sealing the container will help keep excess moisture at bay.

For basements, sprinkle chlorinated lime (commonly called chloride of lime or bleaching powder) over the floor. Let it sit until musty mildew odors disappear. Then sweep it up. Increasing the heat and air circulation into the basement will help this process. Get rid of mildew on tiled walls and bathrooms floors by scrubbing them with a diluted solution of sodium hypochlorite or chlorine bleach, 1 cup of bleach to a gallon of water. Rinse with clean water and wipe as dry as possible. Keep the windows and shower curtain open until the walls and floors are thoroughly dry.

Removing Mildew from Bathroom Caulk

Mildew may be cleaned from bathtub caulk and bathroom walls the same way. If the mildew extends below the caulk, however, there is no point in cleaning it; it will soon return. Better to remove the old caulk and apply new. For walls, there is less chance for mildew to develop if the walls are painted with a high gloss finish rather than matte. For tile grout, try using a commercial spray-on mold and mildew remover. Run the bathroom exhaust fan while taking showers or running the bath to slow the development of mildew.

Outdoor wooden furniture should be sealed and varnished. Unfinished wood should be coated with a paste wax. Except for teak and cedar furniture, all wood and wicker pieces should be brought inside for the winter, umbrellas, too, preferably. Cloth cushions can be sprayed with a mixture of warm water, detergent, and borax. Let it sit for a few minutes, then blast it off with a pressure hose. For stains on canvas, it’s the same, except use naphthalene soap instead of detergent and borax. These methods may not remove all the mildew stains, but it’s about the best you can do.

Mildew Removal Tips for Boaters

Boat canvas is another story. Most on-deck canvas is made of a woven acrylic fabric which has a mildew resistant finish. Clean this by brushing off loose dirt, then washing with a mild soap solution, not a detergent, with warm water (no more than 100 degrees F). Then rinse thoroughly with cool water to remove all soap residues. LUX and IVORY are two mild soaps. Using detergent will compromise the finish and ultimately destroy it. For canvas that’s stained with mildew, use a highly diluted solution containing non-chlorine bleach. Treat the canvas with a 50% solution of white vinegar to discourage mildewing.

For prevention of mildew on sails, always dry them before stowing them. If you do get mildew, apply the mildest mixture of bleach and water possible, then immediately flood them with water to drive out the remaining bleach. Allow them to dry before stowing.