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How to Combat Mold and Mildew

How mold and mildew get a foothold in your home, how to clean and get rid of it and how to prevent its return. Eliminate moisture sources; water and mold go hand in hand.

By the DIY experts of The Family Handyman Magazine

What is mold and mildew?

What’s wrong with a little mold and mildew? As long as they stay put behind the laundry tub, out of sight under the basement carpet, or only peek around the edge of the bathroom wallpaper, who cares? Well, you should, because they’re not only eating away at your house, they could be eating away at your health, too.

Here we’ll take a look at what mold and mildew are, how they affect the health of you and your house and, finally, how you can prevent their growth and get rid of the stuff.

Mold and mildew—big-time consumers

Though there are thousands of different types of mold and mildew, they all have two things in common: The first is that their mission on Earth is to digest the organic world around them. The second is that they all need moisture so their little digestive enzymes can go to work.

There are differences between mold and mildew, but for our purposes, we can call the entire gang mold. Molds are neither plants nor animals. They’re microscopic organisms containing enzymes (responsible for digesting and decomposing) and spores (in charge of reproduction). Mold dwells within the fungi kingdom: a realm that includes mushrooms, yeast and other seemingly unsavory characters. But the truth is, these decay organisms aren’t unsavory at all. Without them, toppled trees, dead animals and fallen vegetables wouldn’t decompose. Our land would get piled higher and higher with dead stuff. We wouldn’t have foods and medicines like cheese and penicillin. The problems arise when mold starts chomping away at things we don’t want them to—affecting the look, smell and structural integrity of your house.

Mold grows in moist places

Mold grows in moist places

Figure A: Mold and Mildew Love Moist and Damp Places

Mold and mildew need only a damp, moist environment and organic material to establish themselves and thrive. Roof and foundation leaks, high interior humidity, overflowing washing machines and more severe forms of flooding are common sources of moisture. Drywall backing, wallpaper, carpet backing, household dust and wood products are commonly attacked organic materials.

How mold and mildew affect your home

Mold needs to consume something to survive, and it’s perfectly happy eating your house if you let it. Some molds and mildews are fond of the cellulose in the paper backing on drywall, insulation and wallpaper. Others have a ravenous appetite for the glues used to bond carpet to its backing. Left unchecked, mold eventually destroys the parts of the drywall, wallpaper and carpet it attacks.

But many molds just like to feast on the every- day dust and dirt that gather in the perpetually moist regions of your house. They won’t destroy your house, but they can sure make it look, feel and smell bad. Mold can mar your walls with white spider web–like growths or clusters of small black specks. It creates the smell we often refer to as “musty.” It can be slippery and dangerous when it grows on damp basement stairs. Molds rarely go so far as to rot wood or do structural damage—they’ll leave that to their fungal cousins—but they can wreak plenty of havoc. We can’t overemphasize that mold needs moisture to get established, grow and reproduce. Mold problems and longstanding moisture or high humidity conditions go hand in hand. To conquer mold, you must also conquer moisture problems. Fig. B shows common hangouts for mold and some steps you can take to minimize its growth and the damage it inflicts.

13 common breeding grounds for mold.

13 common breeding grounds for mold.

Figure B: 13 Common Breeding Grounds for Mold and Mildew

Problem #1
Leaky air-conditioning duct joints, especially those running through a hot attic, create a moist environment for mildew.

Solution
Seal all duct joints with the special flexible mastic available at heating and cooling supply stores.

Problem #2
In warm environments, impermeable vinyl wallcoverings can trap moisture-laden air as it moves from the warm exterior to the cooler interior. Mold degrades the drywall and adhesive behind the vinyl wallcovering.

Solution
Use paint or apply wallcoverings with permeable paper backings that don’t trap moisture on exterior walls.

Problem #3
When washing machines in a room without a floor drain overflow or hose connections burst, water with no point of exit will soak into adjacent carpet, drywall and insulation.

Solution
Always provide a floor drain near the washing machine. Install an overflow pan directly under the machine or install a 1-in. lip at the doorway to contain overflows in main-level or second-story laundry rooms.

Problem #4
Water-resistant drywall used as a tile backer quickly degrades once subjected to moisture.

Solution
Install cement backer board, which will remain structurally sound even if repeatedly subjected to moisture.

Problem #5
Poorly ventilated bathrooms allow surface mold to grow.

Solution
Install a bathroom fan (or at least, open a window) to exhaust moisture. Remove surface mildew by scrubbing the area with a 1/2 percent bleach solution. When the area is dry, prime it with an alcohol-based, white pigmented shellac, such as Zinsser Bullseye, and use a paint containing mildewcide.

Problem #6
Poorly constructed crawlspaces promote mildew growth. Bare earth floors transmit huge amounts of moisture.

Solution
There are many regional differences and solutions. Cover bare earth with 6-mil poly sheeting. Heat, cool and humidify the area the same as the rest of the house.

Problem #7
Freshly cut firewood stored indoors emits huge amounts of moisture.

Solution:
Store it outside.

Problem #8
Humidifiers (especially reservoir-type central units and portable units) provide both a growth medium and a distribution system for mold and mildew.

Solution
Clean and treat the reservoir often with an antimicrobial solution, available at most hardware stores.

Problem #9
The condensation pan directly under the coil of your central air conditioner can harbor mold.

Solution
Before each cooling season, clean the pan with a 1/2 percent bleach solution and make sure the continuous drain is working.

Problem #10
Finished concrete basements that haven’t been thoroughly waterproofed from the outside are problematic. When moisture migrates through the earth and non-waterproofed concrete walls, it can get trapped behind vapor barriers, carpet, layers of insulation and drywall.

Solution
Thoroughly waterproof the exterior of concrete walls before backfilling. Install 6 in. of gravel under concrete floors during construction to prevent moisture from wicking up through concrete floors and into floor coverings.

Problem #11
Yards that slope toward foundations invite water to enter basements and crawlspaces.

Solution
Regrade yard surrounding house so it slopes away at a rate of 1 in. per foot.

Problem #12
Improperly flashed or caulked windows (and those with large amounts of surface condensation) let moisture seep into the surrounding wood, drywall and insulation.

Solution
Properly flash and caulk windows during installation; minimize condensation with good ventilation and airflow.

Problem #13
Leaky flashings and shingles allow rain to infiltrate attics, insulation, eaves and other areas that can trap moisture and be difficult to inspect.

Solution
Perform yearly roof inspections—even if you do it from the ground with binoculars.

Note: You can download and enlarge Figure B in “Additional Information” below.

Mold and mildew can make you sick too!

Besides damaging your house, mold can cause severe health problems. One consultant we interviewed confessed he crawls around in moldy places day after day, month in and month out, and never suffers ill effects. Othersmdash;some estimate about 10 percent of the populationmdash; are severely allergic to mold. It’s primarily the dinky reproductive spores that people react to. Twenty of them sitting side by side could fit across the period at the end of this sentence. That means they’re hard to filter out. The spores also have an incredible “hang time” (as my teenage son would say); they’re able to stay suspended in midair for hours on end. That means they’re easily inhaled.

With even slight exposure to molds and spores, sensitive people may experience headaches, runny noses, skin rashes, nausea, sinus problems, memory loss and coughs. They may feel listless for long periods of time. In short, they feel as though they have a perpetual case of the flu. Newborns, the elderly, the sick, and those with compromised immune systems can be affected severely, even fatally. Babies and toddlers, who love to crawl around on possibly moldy carpets and stick possibly moldy things in their mouths, also are highly vulnerable to mold-induced illnesses. Supersensitive people often go to extremes to rid their houses of the materials that harbor the dirt and dust that molds feed on. They’ll replace soft, textured materials with smooth, hard surfaces that are easier to keep clean and less likely to trap debris and moisture. Out go the carpets and draperies; in come hardwood floors and metal window blinds. Out go the cushy couches; in come the vinyl chairs.

Tightly sealed newer houses may be better at holding in heat, but they’re also more likely to trap moisture and spores. Mechanical ventilation, like an air-to-air heat exchanger, is critical for healthy air quality in tightly sealed new homes.

In truth, most of us fall somewhere between the two extremes of invincibility and super-sensitivity. But even “normal” folks will react to unusually high concentrations of mold and spores. And the time you’re most likely to stir up spores and inhale and ingest them is the very time you’re trying to get rid of the stuff. That’s when you need to be the most careful.

How to get rid of it without making matters worse

Step one in getting rid of mold is to fix the moisture problem that’s setting the stage for its growth. This is key. You can scrub, dispose of and replace moldy materials, but until you fix the problem, mold will keep returning. The fix can be as simple as sealing up leaky air-conditioning ducts (Fig. B) or as daunting as reshingling a leaky roof or regrading your yard so water runs away from, rather than toward, your foundation. Sewer backups and floods also set up ideal environments for mold and mildew growth.

Once the moisture problems are fixed, get rid of the moldy materials carefully. Rough handling of damaged materials will not only stir up spores and spread them even farther around your house but also launch zillions of spores into the air, where you’ll inhale them. One square foot of moldy drywall can harbor more than 300 million mold spores; slam dunk that onto the basement floor and you’re just opening another Pandora’s box. Even dormant spores inhabiting dried-out materials are irritating to inhale, and if they find moist environs again, they can zip back to life and establish new colonies.

Follow these procedures when removing damaged materials (Fig. C):

  • Wear a good cartridge-type respirator, available through a medical or safety equipment supplier. One good mask is a triple-seal respirator with a P100 filter cartridge. A simple dust or particulate mask doesn’t offer adequate protection. Wear gloves and goggles if you’re scraping.
  • If your basement or main floor has flooded, get it as dry as possible within the first 72 hours, before mold and mildew can get established. Drill holes in drywall or remove lower sections of it to let the inner wall and insulation dry out.
  • Close off any ventilation grilles with polyethylene sheeting and duct tape. Shut down your furnace so the blower doesn’t spread spores and dust throughout the house.
  • Remove everything—furniture, pictures, lamps—from the room.
  • Tape poly sheeting on all four edges across the door opening and cut a slit in the middle from top to bottom. Then tape another flap across the top.
  • Place a box fan in the window blowing outward.
  • Use a garden sprayer containing water and hand-dishwashing detergent to lightly mist insulation, carpet and other materials before you remove them.
  • Move slowly and deliberately so you don’t stir up spores as you work.
  • Double-bag or double-wrap all the materials you’ll be discarding.
  • Scrub all remaining hard surfaces with a 1/2 percent household bleach solution.

How to handle moldy building materials

How to handle moldy building materials

Figure C: The Smart Way to Get Rid of Moldy Building Materials

The key to removing moldy materials is containment and thoroughness. Seal off the area. Create a crude "air lock" door to contain spores and dust by covering the opening with a sheet of poly slit in the center, then cover that with another sheet or flap. Wear a respirator and work slowly and surely. Double-bag or wrap all materials, then wash all remaining hard surfaces with a 1/2 percent bleach solution and let dry.

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