How to Get Rid of Mold on Walls (Permanently)

Cookie banner

We use cookies and other tracking technologies to improve your browsing experience on our site, show personalized content and targeted ads, analyze site traffic, and understand where our audiences come from. To learn more or opt-out, read our Cookie Policy. Please also read our Privacy Notice and Terms of Use, which became effective December 20, 2019.

By choosing I Accept, you consent to our use of cookies and other tracking technologies.

Video

Open Up Moldy Walls

  • Pry off baseboards and trim from contaminated areas with a pry bar and block of wood.
  • Probe heavily stained or moisture-swollen walls using a screwdriver to discover and open up moisture damage and hidden mold in the insulation and wall framing.

How to Check for Mold Inside Your Walls

  1. Locate the center of the area most likely to have mold inside.
  2. Shut off power to the area at the electric service panel.
  3. With a pencil and straightedge, lightly mark a square approximately 6 inches by 6 inches.
  4. Cut along the outline with a drywall jab saw.
  5. Remove the cut-out and inspect its back for mold.
  6. If there is no insulation in the wall, look at the back wall. Also, hold a small mirror inside and shine a flashlight on the mirror to inspect the back of the drywall.
  7. If there is insulation, any mold on the drywall or studs will have spread to the insulation. So, the presence of mold on insulation usually means mold on other building materials. 

Before You Begin

Removing mold from inside walls is a four-step process: removing moldy drywall and other materials; killing mold; encapsulating remaining mold; and rebuilding part or all of the wall with new drywall, insulation, and other building materials.

  • Removal/Disposal: Moldy drywall and insulation must be removed. None can be reused.
  • Kill Mold: Spray the mold with a liquid biocide to kill it. Alternatively, exposing the mold to air and light for long enough will kill it. Do not use household bleach.
  • Encapsulate Mold: Cover the mold with a fungicidal mold encapsulant. Choose a coating that contains the active ingredient calcium hydroxide. Do not use ordinary house paint.
  • Rebuild: The area must be rebuilt with new building materials. New insulation is added to exterior walls (interior walls do not require this). Drywall is hung, then painted. For areas with persistent mold, you may even choose mold-resistant drywall.

Tip

Citing environmental concerns, the EPA's position on mold biocides is that they are permitted but not recommended. The EPA makes an exception for areas where immune-compromised individuals live. The EPA does not ban biocides. Instead, it recommends that the mold be killed with ventilation and light.

How to get rid of mold on walls

Many people first notice they’ve got a mold problem when they see it growing on their walls. Check in the corners near the ceiling and floors in rooms with high moisture levels, such as kitchens, bathrooms, laundry rooms, and basements. 

You’ll need: 

Bleach

Water

White vinegar 

3 percent hydrogen peroxide

2 spray bottles

Scrubbing brush

Method:

Step 1: Make a solution of one part bleach to three parts water in the spray bottle.

Step 2: Saturate the mold and surrounding area on the wall.

Step 3: Let the solution soak into the mold for 10-15 minutes.

Step 4: Using the scrubbing brush, remove the mold and stains.

Step 5: Repeat as necessary to remove all the traces of mold and mildew.

Step 6: Make a 50/50 mixture of white vinegar and hydrogen peroxide in the second spray bottle.

Step 7: Spray the cleaned surface and allow it to absorb and air dry.

This method works because it addresses the visible mold, as well as the underlying roots that often go untreated. Surprisingly, vinegar and hydrogen peroxide are both more effective at killing mold roots than bleach. Because they work best on different types of mold, try to use them together to cover all the possible varieties of mold you might be dealing with.

Pro Tip: If you don’t have hydrogen peroxide at hand, you can also clean mold with vinegar and baking soda instead.

Tips for Preventing Mold on Walls

The most effective way to prevent mold and mildew from growing on your walls is to control moisture in your property. You can minimize the humidity within your home by using a dehumidifier and ensuring all rooms are well ventilated.

Condensation can also cause mold in your home. However, you can help to prevent it by insulating roofs, windows, exterior walls, and pipes.

Bathrooms and kitchens are particularly prone to mold and mildew. Ensure that these rooms are cleaned regularly to prevent spores from growing.

Things You’ll Need

  • Plastic drop cloth
  • Spray bottle
  • Baking soda
  • Vinegar
  • Detergent
  • Bleach
  • Toothbrush or sponge
  • Electric fan
  • Pencil
  • Utility knife
  • HEPA vacuum
  • Drywall
  • Drywall screws
  • Screwdrivers
  • Joint compound
  • Sandpaper

How to get rid of mold spores in the air

No machine will ever be able to get rid of all the mold that could enter your property, it’s simply too small and too common. However you can reduce your risk by using an air scrubber, UV light treatment, or fogger designed for use against mold spores.

How to use an air scrubber for mold

Air scrubbers are usually part of a HVAC system, and are basically a series of superfine filters. The air that is drawn into your HVAC system from outside runs through the scrubber, and that removes harmful particles such as mold spores. Some scrubbers also contain purifying filters that kill pathogens and bacteria, and many businesses are now using industrial air scrubbers for COVID-19 prevention.

A properly installed air scrubber can remove 99 percent of contaminants from the air, making it a great option if you live in a mold-prone area or are immunocompromised. What an air scrubber can’t do, however, is remove all the mold from your home. Every time you open a door or window, or a seal isn’t quite secure, air will enter your home that hasn’t been scrubbed and will almost certainly contain mold spores. Speak to a technician to learn about the best HVAC air scrubber for your system.

Air scrubbers vs air purifiers

Air purifiers do the same thing as air scrubbers, but on a smaller scale. They’re basically portable air scrubbers. If you’re only worried about the air quality in one room, purchasing an air purifier will be faster and cheaper than installing an air scrubber designed to clean the air in your whole house.

Using an air scrubber vs UV light

Another solution is to install a UV light attachment into your HVAC system instead of an air scrubber. This is often a cheaper and simpler solution, and UV light has germicidal properties that can kill all kinds of bacteria and pathogens, including mold spores. UV lights are also unobtrusive, and won’t have any impact on your HVAC system’s performance. By comparison air scrubbers can force the system to work harder to push the air through increasingly fine filters, resulting in a drop in power.

Mold bomb foggers for cars

Just like your property, your car can also suffer from mold. Foggers release a fine mist of fungicidal solution designed to get into all the nooks and crannies where mold might be hanging out. While many are safe to use in vehicles, always check the instructions and make sure to air the car out afterward to prevent breathing in any harmful chemicals.

Killing Mold in the Bathroom Drywall and Other Humid Areas

Using stain removers for killing mold from drywall and sheetrock

There are some cases where you could simply spray moldy drywall with a mold stain remover. Clorox Clean Up is cheap and works well, but there are many others. You can use mold stain remover when the black mold is a simple “surface mold” caused by humidity. If you aren’t sure if it’s surface mold, or something more serious, most honest mold removal professionals will offer a free quote. 

The most common example of this scenario is in a shower, along the wall or ceiling drywall.  When people take long, steamy showers, the shower walls & ceilings get wet with humidity and eventually black mold will start to grow.  You can lightly spray the walls with your mold stain remover, wait a couple minutes, and wipe it off. Repeat as needed. But keep in mind that unless you start drying out your bathroom after showering, the mold will eventually return.

If you are looking for tips on removing humidity from your furniture and clothes to reduce the chances of having mold, here is an article that might help.

FacebookTweetLinkedInEmail

Mold Removal Safety Precautions

If you have to remove mold concentrations or perform any black mold removal covering more than a few square feet, we recommend you take these precautions:

  • 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.
  • 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.
  • Wrap and tape moldy carpeting in 6-mm plastic, and double-bag mold-infested debris in garbage bags for disposal.
  • To control airborne spores, moisten moldy areas with a garden sprayer while you work.
  • Turn off your furnace and air conditioner and cover ducts and doors to contain spores.
  • Keep your wet/dry vacuum outside when you vacuum.

Different Types of Mold

Although most mold on drywall looks like black spl

Although most mold on drywall looks like black splotches, mold can appear in various shapes and colors, none of which actually determines the species of mold. Learn the different types of mold so you can detect which kind has affected your home.

Black Mold: Black mold is often found inside houses with excessive moisture damage. The mold itself isn’t harmful, but it has the potential to produce mycotoxins that could potentially cause harm to people and pets if left untreated over a long period of time.

White Mold: White mold often grows in cool, damp environments such as basements and is often confused with efflorescence, which is a crystalline deposit of salts that can form when water is present. To test it, spray it with water — if the spot doesn’t dissolve then it’s most likely mold.

Blue Mold: Blue mold has a bluish-green color, can grow within 24 to 48 hours and requires little moisture to develop. It can be found in drywall, wallpaper, ceilings, and insulation that has been damaged by water. It can also be found in areas that are often damp such as bathrooms.

Green Mold: Green mold may be identified by its greenish hue and is found in dark, damp recesses. Like blue mold, it’s often found in damp areas like bathrooms or dark corners. 

Spray mold on walls with white vinegar to get to the root of the problem

While bleach works well to kill surface fungus and remove the ugly marks on the walls caused by mold, it doesn’t penetrate deeply into the drywall, and so it leaves the mold’s “roots” undisturbed. That means the problem is likely to reoccur, sometimes within days.

To try and kill mold beneath the surface, spray undiluted white vinegar onto the affected area and let it dry. Don’t worry about the odor; the smell will dissipate once the vinegar is completely dry.

Photo: istockphoto.com

What is Borax?

Borax is a natural product with a variety of uses. These include being used as:

  • a deodorizer;
  • a cleaning solution for drains and toilets;
  • an insecticide;
  • an herbicide; and
  • a fungicide.

It costs only a few dollars, and can be bought in supermarkets.

Dealing with Mold on Drywall

As we just said, since mold cannot be completely removed from drywall, the drywall must be removed and replaced. This must be done with care because cutting into moldy drywall causes mold spores to become airborne and spread.

The U.S. Environmental Protection Agency (EPA) advises that if mold covers more than 10 square feet, a professional remediation company should be hired to remove the mold. If it is a smaller job that you plan to handle yourself and you have any health concerns, speak with your doctor to make sure it is safe for you.

Mold on drywall in closetMold on drywall in closet

First the work area must be prepared. Furniture and other items should be removed from the area if possible. Otherwise, they should be covered securely with sheets of heavy plastic to protect them from mold spores.

Plastic sheets should be taped over heating and air conditioning vents to prevent mold spores from entering your heating, ventilation and air conditioning system. Hi-hats hould also be covered with plastic.

If the room is small, a large sheet of heavy plastic can be taped over the doorway to keep mold spores from drifting out of the room and into other areas of the home. Simply closing the door is not enough, because mold spores can drift under the door or otherwise make it past the door. If the room is large but you’re only working in a small area, mold remediation professionals recommend using two-by-four wood studs, large sheets of heavy plastic, and duct tape to cordon off the work area and keep mold spores from spreading throughout the entire room.

The floor should also be covered with large sheets of plastic, to prevent the flooring from becoming contaminated with mold.

First the drywall should be sprayed with water to prevent mold spores from becoming airborne as the drywall is taken down. The moldy pieces of drywall should be enclosed in heavy plastic trash bags before you carry them through the house, so as to prevent scattering mold spores as you go.

Of course, personal protective gear should be worn during the mold removal process, including disposable gloves, disposable hair and shoe covers, and an N-95 or N-99 face mask. The process of removing drywall that is contaminated with mold exposes you to mold spores that can make you sick if you fail to take the necessary safety precautions.

Sign up for the Newsletter

Get the latest This Old House news, trusted tips, tricks, and DIY Smarts projects from our experts–straight to your inbox.

Tags