How to Identify Mold

Mold is everywhere. It's a type of fungus that grows from tiny spores that float in the air. It can grow almost anywhere that spores land and find moisture and a comfortable temperature, between 40 and 100 degrees F. Typically that includes about every damp place in your home.

You can easily spot the most visible type of mold, called mildew, which begins as tiny, usually black spots but often grows into larger colonies. It's the black stuff you see in the grout lines in your shower, on damp walls, and outdoors on the surfaces of deck boards and painted siding, especially in damp and shady areas. A mildewed surface is often difficult to distinguish from a dirty one. To test for mildew, simply dab a few drops of household bleach on the blackened area. If it lightens after one to two minutes, you have mildew. If the area remains dark, you probably have dirt.

Mildew is a surface type of mold that won't damage your home's structure. But other types of mold cause rot. Probe the suspect area with a screwdriver or other sharp tool (see photo 3). If the wood is soft or crumbles, the fungi have taken hold and rot has begun.

If you have a high concentration of mold, you may smell it. If you detect the typical musty odor, check for mold on damp carpets, damp walls, damp crawlspaces and wet wood under your floors, wet roof sheathing and other damp areas. Clean up these infestations right away before they get worse.

Removing Large Infestations Requires Precautions – And Work!

You can scrub away the surface mold common to bathrooms, decks, and siding in a matter of minutes with a 1-to-8 bleach/water solution. But often mold grows and spreads in places you don't notice, until you spot surface staining, feel mushy drywall or detect that musty smell. If you have to remove mold concentrations covering more than a few square feet, where the musty odor is strong or where you find extensive water damage, we recommend that you take special precautions. You want to not only avoid contaminating the rest of the house but also protect yourself from breathing high concentrations of spores and VOCS.

• Wear old clothes and shoes that you can launder or throw away after the cleanup work
  
  
• Wear special N-95 or P-100 respirators, in addition to goggles and gloves. See the Buyer's Guide for a source.
  
  
• Set an old box fan or a cheap new one in a window to ventilate the room while working. Throw it out when you're done cleaning, because the spores are almost impossible to clean off. Tape plywood or cardboard around the window openings so the spores can't blow back in (shown in photo 1).
  
  
• Wrap and tape moldy carpeting in 6-mil plastic, and double-bag mold-infested debris in garbage bags for disposal (see photos 1 and 4).
  
  
• To control airborne spores, moisten moldy areas with a garden sprayer while you work (as shown in photo 1).
  
  
• Turn off your furnace and air conditioner and cover ducts and doors to contain spores.
  
  
• Keep your wet/dry vacuum outside when you vacuum (see photo 5).

Moisture Damage and Large Infestations Go Hand in Hand

Photos 1-7 demonstrate cleaning under an old leaky window where wind-driven rain frequently got into the wall and gave mold a foothold.

You have to open up the wall to get at the mold growing inside (see photo 4). Since you have to repair the wall anyway, don't hesitate to cut the drywall back beyond the obvious damage to find all the mold and let the wall dry out. To avoid cutting electrical wires, poke a hole through the damaged section and locate the wires first. Turn off the power to the outlets before you cut.

If the moisture damage has been neglected or gone unnoticed for long, you're likely to find rot. Where possible, remove and replace soft, spongy studs and wall sheathing. Where removal is difficult, treat the affected areas with a wood preservative (available at home centers) after cleaning the wood and allowing it to dry. Then double up rotted members with pressure-treated wood.

Complete the initial cleanup by vacuuming up the debris (see photo 5). Thoroughly clean the wet/dry vac afterward by disposing of the filter and washing out the tank, hose, and attachments with the bleach-and-water solution.

After scrubbing the surfaces (see photo 6), simply allow the bleach solution to continue to penetrate the surfaces and dry. Wash concrete floors with TSP, automatic dishwasher detergent or a chlorinated cleaner such as Comet.

Set out dehumidifiers and new fans to dry the now-cleaned areas for at least three days, then check them (by sight and smell) for mold. If you discover more mold, clean again with bleach.

When you're sure the mold has been eliminated, seal the wood surfaces with pigmented shellac like BIN or an oil-based primer like KILZ (see photo 7). Repaint cleaned wall surfaces with a regular latex paint that contains a mildewcide to help stop future mold growth. And keep in mind that if the moisture returns, mold will return.

Tips for Preventing Mold

The key to stopping most mold is to control dampness. The worst infestations usually occur in damp crawlspaces, in attics and walls where water has leaked in from the outside, and in basements with poor foundation drainage. Stopping leaks, ensuring good ventilation in attics, keeping crawlspaces dry, and routing water away from the foundation are the best defenses.

Mildewcide in paint is usually effective for controlling surface mold in damp rooms like bathrooms and outside in shady areas. Many paints already have mildewcide in them. Check with your paint dealer to be sure. You can add mildewcide, although you might void the paint warranty.

Techniques for Cleaning Surface Mold

Surface molds grow in just about any damp location, such as the grout lines of a ceramic tiled shower. They're easy to scrub away with a mixture of 1/2 cup bleach, 1 qt. water, and a little detergent. The bleach in the cleaning mixture kills the mold, and the detergent helps lift it off the surface so you can rinse it away so it won't return as fast. You can also buy a mildew cleaner at hardware stores, paint stores, and most home centers.

Even for simple cleaning, protect yourself from contact with mold and the bleach solution by wearing a long-sleeve shirt and long pants as well as plastic or rubber gloves and goggles.

TIP: Special gloves made of nitrile are as tough as latex but thinner and more protective. See the Buyer's Guide for a source.

If the mold doesn't disappear after light scrubbing, reapply the cleaning mix and let it sit for a minute or two. Then light scrub again.

Seal the clean surfaces when they're thoroughly dry to slow future moisture penetration. Apply a grout sealer ($5 to $25 per quart from tile shops and home centers) to tile joints.

CAUTION: Don't mix ammonia or any detergent containing ammonia with bleach. The combination forms a poisonous gas.