A Moldy Basement is the Worst. Here’s How to Clean It Up

moldy basement

You’ll know it when you smell it (think damp, musty, like rotting leaves) or when you see it (white, black, brown, or even gray, yellow or green splotches all over the place). When mold rears its ugly, smelly head in your basement, it’s only a matter of time before it spreads and claims the rest of your home for its own. Don’t let it. Get rid of the mold — and take steps to make sure it stays away.

The Problem With Mold

Growing mold releases microscopic spores – tiny little seeds – that drift in the air. It’s almost unavoidable that some will come inside your house. The problem begins when they find the conditions they need to develop into mold: dark, damp, stagnant or mostly still air and temperatures above freezing (but somewhere below boiling).

Some molds are considered “toxic,” even to healthy people. Toxic molds produce chemicals called mycotoxins, which may cause serious illness, infections and possibly even fatal conditions.

Most species of mold are relatively harmless. In fact, only an “estimated 6 to 10 percent of the general population” are sensitive to mold allergens, according to the Centers for Disease Control and Prevention. For these people, higher exposure levels may lead to rashes, watering eyes and runny nose, coughing, sinus congestion and even difficulty breathing. There’s also a higher incidence of mold allergies in asthmatics, although whether mold causes the asthma has not been established. People with compromised immune systems and those with established lung disease may experience a higher risk infection from molds, suggests the Washington State Department of Health.

Some molds are considered “toxic,” even to healthy people. Toxic molds produce chemicals called mycotoxins, which may cause serious illness, infections and possibly even fatal conditions. Commonly called “black mold,” many of these, such as the greenish-black Stachybotrys mold and its cousin, Memnoniella, grow on popular building materials such as plasterboard, wood and paper.

You shouldn't panic over every mold you encounter – even if it appears black. You should, however, make an immediate plan of action to remove the mold and follow sensible safety procedures during the cleanup. Most basement mold cleanups are something you can DIY, as long as you feel capable of tearing up materials and performing the repairs yourself. If the mold covers the entire basement or if you suspect it’s growing in areas you feel uncomfortable handling, such as inside air conditioning vents, consult a mold remediation professional instead.

Gather Supplies, Find the Moisture Source and Dry Out

Proper preparations are critical. Gathering supplies is the first step. Then, permit yourself one inspection trip, armed with personal safety equipment, to determine the scope of the problem and to eliminate the source of moisture, if possible.

  • Plastic sheeting, 4-millimeter thickness minimum
  • A respirator
  • Spray bottles
  • Disposable rags or paper towels
  • Large garbage bags
  • 5-gallon buckets
  • Rubber or latex gloves
  • Measuring cup
  • Borax or vinegar
  • Bleach
  • Dehumidifier
  • Commercial-grade HEPA vacuum (optional, but recommended)
  • Coveralls
  • Goggles or similar eye protection
  • Scrub brush or broom

If the basement is wet from a flood, the source is obvious. Other possibilities include gutters that end too close to the house, improperly graded soil around the house, leaks in the foundation, a dryer that isn’t vented to the outside and leaking pipes. Closely examining the area of mold should quickly reveal the water source. Then, take steps to eliminate the source. Call in a professional for foundation issues or other repairs as needed. Only after the problem is resolved will you be successful in eradicating the mold. All it takes, after all, is a single spore to grow into a colony again.

Closely examining the area of mold should quickly reveal the water source. Then, take steps to eliminate the source. Call in a professional for foundation issues or other repairs.

Once you’ve cut off the moisture source, hang sections of plastic sheeting over door openings and heating or air conditioning vents to isolate the infected areas from the remainder of the basement or house. At this point, there’s less mold outside than indoors, so open a window, if possible, to provide ventilation and fresh air circulation. A fan, set in the window and pointed outside, or aimed at the ceiling, will also help circulate the air. Avoid blowing it directly at the mold or turning it on high, which will stir up the mold and encourage it to release spores.

Consider running a heater or dehumidifier to aid in drying out the basement. Be sure to wipe the appliance down with a disinfecting mold cleaner when you are done with the removal to prevent a re-contamination.

Choose and Mix Up Your Mold Removal Solution

Here’s the truth about expensive mold removal solutions: You don’t need them. You can throw away most items covered with mold and scrub the surrounding areas with detergent and water or a natural product to remove the mold residue. It’s cheaper than commercial fungicides and doesn’t burn your eyes, lungs and skin.

If your basement flooded, sanitize it with bleach. Bleach reduces the mold count – it doesn’t completely kill it – and neutralizes harmful bacteria. Mix chlorine bleach with warm water in a bucket at a ratio of one cup (8 ounces) of bleach per gallon of water. As you work and the solution gets dirty, be sure to flush it and mix up fresh batches.

A better choice for removal is either straight vinegar (smaller areas) or borax and water (larger areas). Sure, vinegar has strong fumes, but they will dissipate within a few hours. Borax, another completely natural product, leaves a powdery residue behind as it dries, which will repel mold spores before they begin to grow. Mix about 1 cup of borax per gallon of warm water in a bucket and refill a spray bottle as necessary.

Step by Step: Attack Mold Like a Savage

mold cleanup
So, you’ve found the source of moisture, fixed the problem and dried out the basement. You’ve gathered your tools, chosen a mold removal solution and donned your protective wear. It’s time to give the mold in your basement eviction papers.

  1. Look for mold not only on exposed surfaces, but also in cracks and crevices that surround the source of moisture. Whenever you find mold, spread your search farther than the original spot. In many cases, visible mold turns into invisible or hidden spots of contamination.
  2. Remove boxes, bags and other items stored in the area. Place them in garbage bags so as to contain the mold while you are cleaning the basement. You may need to tear away wall sheathing – drywall, paneling or similar – to expose the wall interior. Throw away sheathing or insulation that comes in contact with mold. There’s no good way to clean it.
  3. Rip up carpets and other flooring material if you suspect mold underneath. If you find it’s okay, often you can reuse the material after wiping it down with solution or steam cleaning the carpet. If you do find mold, however, just throw it away. The cost to replace it is insignificant in comparison to your family’s health.
  4. Fill a spray bottle with vinegar, borax and water or bleach. Spray the walls, pipes, windows or other permanent fixtures until they are thoroughly coated with the solution. Allow it to set for an hour or two. Take advantage of the break to slip out of the basement (remember to remove your protective wear before you walk through the rest of the house) to carry the bagged items outside.
  5. In your driveway or backyard – well away from windows or doors – sort the bagged items. Contaminated building materials should go immediately to the trash. Cardboard, paper and other absorbent materials are best thrown away, with the exception of clothes, which may be washed in hot water with bleach or borax added. Plastic, metal and other moisture-resistant materials are often safe to simply wash down with fresh solution and air dry in the sun. Use your best judgment to decide what can be saved and what cannot.
  6. When you return to your basement, spray the surfaces down again to refresh the mold-killing properties. Spray past the contaminated surfaces – overdoing it is better than leaving spores to grow again. Use a brush on vertical surfaces such as walls, wood framing and windows to scrub the moldy surface. Rinse brushes frequently in fresh solution to prevent re-contamination. Scrubbing physically removes much of the now-dead mold. Try a broom on floors or hard-to-reach spots and switch to cloths as needed.
  7. Now that the mold is dead and scraped from the surfaces, you must remove it from the property. Scrubbing and wiping with fresh water is tedious, but effective. Go over the area repeatedly, changing your rinse water every few minutes. Experts also recommend that a HEPA vacuum be used to clean contaminated areas (at a pace of one minute per foot) to ensure that all traces of mold are gone.
  8. If you used borax to clean the mold, lightly spray the surfaces one final time. Then, when you are satisfied that every contaminated item has been removed and all areas are cleaned and thoroughly rinsed, you must allow your basement to dry. It can’t be stressed enough: You can’t allow moisture in your basement. Wipe down treated surfaces with clean rags to start. Ideally, purchase a dehumidifier, if you don’t already have one, and set it up in the middle of the area.
  9. After the basement is dry, repair and redecorate it. Install new insulation, sheathing and flooring, if necessary. Replace items removed from your basement during cleanup (provided they are mold-free). Just take your time in treating, rinsing, drying and repairing your basement. Rushing generally results in an unwelcome, permanent guest.

Stop Mold From Inching Its Way Back

You’ve evicted the mold, but that’s not enough. More is sure to come if you don’t take steps to keep it away. Remember, mold needs a source (spores), food (biodegradable building products, dead insect parts, skin particles, etc.), water, hospitable temperatures and darkness. So, your job is to eliminate as many of these factors as you can.

  1. Any source of moisture, from over-watering plants to leaks, should be eliminated. This is especially true in the basement, where temperature differences between the upstairs and downstairs encourage the formation of humidity and condensation. Running a dehumidifier year round and installing vents, especially in the bathroom, helps significantly.
  2. It might seem unrelated, but even proper insulation helps control moisture. Insulation always pays for itself in several ways. Vapor barriers are also essential, even in a dirt-floor area. Run unbroken sheets of plastic across the dirt floor and cover with more dirt to prevent moisture migrating up from the soil.
  3. Install a hygrometer to monitor your relative humidity in the basement. Humidity levels above 50 percent indicate that the environment is ripe for mold growth. When used in combination with a dehumidifier, it can also tell you when you may have a moisture problem. That is, in a temperature-controlled environment with a dehumidifier running, your RH levels should remain fairly stable. If the level suddenly rises, you should suspect you have a leak or other moisture source and investigate.
  4. Speaking of controlling the temperature in your basement, it’s true. While you may not want to heat it to the same temperature as the rest of the house, heating it to about 60 degrees during the winter months is a smart move. Below-ground structures – especially concrete or masonry – easily stay musty and damp as they are more absorbent and transfer temperature differences through their thickness. Heating your basement helps to maintain consistent relative humidity levels.

At this point, your basement should be free of mold and unlikely to host any more. Not only should it look much better, but it’s healthier, and you saved a lot of money by doing it yourself.