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Chapter 3: Steps for Mold Remediation

This chapter will be an overview of the steps one takes to remove an active mold problem. We will begin by discussing how to choose appropriate locations for remediation equipment and move on to discuss the removal and disposal of building materials contaminated by mold.

When you know there is a mold problem present, it’s time to act and put a plan in place to protect people who work in the space, as well as your investment. The exact mold removal process will differ depending on the type of space you’re working in, the severity of the problem and the outdoor conditions in the area, but you can follow these general steps for mold remediation:

Step 1: Protect Staff and Personnel

After discovering a mold problem, the first thing that is necessary if there are personnel actively working on site is to ensure they stay safe. Use barricades, tape, and signage to indicate that the area is off-limits. If there are currently people with workstations who operate there, they need to be relocated to a new space immediately.

Step 2: Perform Preliminary Testing

If large colonies of mold are easily visible, testing may not be necessary — however, pretesting is always a good idea to determine the extent of a mold problem and provide comparison values for post-testing. In situations where personnel is exhibiting symptoms of exposure to mold, testing may be the only reliable way to verify that mold exists and is the cause of the problem.

The most reliable form of testing will be SPM levels in your building air. While the 10,000 SPM standard established earlier in this guide is a general rule, areas with a high concentration of particulate matter present in outside air may be held to different standards.

You will most likely use a third-party testing company to run lab tests on your test samples. Multiple air samples should be collected and typically an even larger number of surface samples. This is because of the more homogenous makeup of air samples vs. localized surface testing.

Surface testing can also be used to check for the presence of a mold infestation, but it’s often less accurate. A surface test can potentially produce a false positive if there is a high concentration of spore material in a small area — for example, if a moldy piece of food is present nearby. For this reason, we recommend taking many surface samples to increase your level of confidence in this type of testing and use it in combination with air sampling.

Step 3: Prevent Cross-Contamination

Cross-contamination is a real risk when working around areas contaminated by mold. While smaller jobs (inside of 30 sq. ft. of the affected area) can sometimes be contained without the use of negative air and other measures that prevent cross-contamination. You can build a dust barrier using PVC pipe and 6-mil polyvinyl.

In a commercial setting, avoiding cross-contamination is an essential part of the mold remediation process. Mold spores spread through the air, so transporting materials with mold growth on them, even when they have been dried out, can pose a risk of cross-contamination.

A negative-air environment is created by ducting air movers so that they pull air out of your work space. Ducting should be attached to air movers using an airtight seal and vented to the outside atmosphere somewhere relatively far from where remediation work is being done.

A dust barrier must still be used to seal off the affected area before an effective negative air environment can be created. Measure the output of your air movers so that they achieve between 6 and 12 ACH to keep contaminated materials moving out of the building.

When treating affected areas, it is important not to agitate surfaces that could spread mold using power-washers or other cleaning methods that might disturb spores on the surface of the material.

The dust barrier should remain in place throughout the remediation process, and all personnel working to disinfect and remove materials on which mold has grown should wear proper respiratory protection, eye protection, and in some situations even more protective gear. Only after the area is declared clear of hazardous spore counts by a third-party assessment and any required inspectors can the barrier be taken down.

Step 4: Disinfect or Remove Affected Materials

With your equipment in place, the next step in resolving a mold issue is to remove any dried out contaminated material. This includes soft furniture, food and any other substances that might become food for mold if left in place. All this material should be removed as soon as possible.

Depending on how prevalent mold growth is in your building, it may be possible to clean mold from affected drywall. Use a drop cloth or masking to protect the area around the drywall that will be removed from any disinfectants or other chemicals that could potentially discolor intact drywall.

Remember, respirators and protective clothing should always be used.

Step 5: Place Dehumidifiers

Place industrial dehumidifiers in areas where high levels of moisture are still present. Measure the square footage of the area that you need to disinfect and calculate the volume of air you need to dehumidify and select the right equipment.

Set your dehumidifiers up in the center of your space. If you are using more than one, make sure they are facing away from one another. Distance from walls to dehumidifiers should be the same as a distance between dehumidifiers themselves if possible.

Allow dehumidifiers to run constantly to remove moisture from the air.


For smaller mold colonies that don’t require significant removal of materials, you can clean and disinfect the affected area, install mold remediation equipment and test to see if the issue continues. When materials are being removed, it is to clean the area following removal of the contaminated materials to eliminate any smaller colonies that may already be forming.

Hydrogen peroxide in a 3% solution makes an effective disinfectant that will kill nearly all types of mold. You can use a spray bottle and a brush to apply the solution to surfaces in the contaminated area, and then scrub them down. Keep in mind that this solution can act as bleach on some surfaces.

Commercial solutions are also available for disinfecting an area infested with mold. From mold and mildew stain removers to advanced peroxide cleaner, various substances are available that can be used on a range of materials, such as wood, concrete, hardie board, cinder block, and vinyl siding. Some brands even have options that are non-toxic or biological-based, as well.

Media blasting has been employed in some instances as an alternative method to remove mold colonies. Dry ice blasting uses vapor from frozen carbon dioxide to kill and remove mold in particularly hard to reach places, and other blasting techniques include media blasting with beads, sand or natural substrates.

While these techniques might be appropriate in niche situations, they are often very damaging to space and not cost-effective. Using a traditional fungicide is usually cheaper and just as capable.

Apply your cleaning agent or disinfectant to the moldy drywall. You don’t need to soak the area — only enough disinfectant to cover the area one or two times is needed. Once the disinfectant is applied, put on gloves and scrub the area down. When no more mold is visible, set up an air mover to blow directly at the freshly cleaned drywall.

Seal and protect the newly cleaned drywall by applying a mold-resistant coating once you are finished. You can also use mold-resistant primer or paint.

If the drywall is unpainted and mold has grown into it, or the drywall is too contaminated to clean, you may need to cut it out. When you do this, cover the area with protective plastic to keep spores from spreading and cross-contaminating other areas when you cut into the old drywall.

Use a marker or carpenter’s pencil to outline the area of the wall that you’re going to cut away. Keep in mind, you need to remove more drywall than just the extent of mold growth. When removing drywall, the area removed should include all material between the two outermost studs that encompass all mold growth (read more about mold growth here)

Use a razor blade to cut along your marks and remove the affected area of drywall. Set the removed piece down with the protective plastic facing the floor. Vacuum the area using a HEPA filter vacuum and place air scrubbers in the area if they were not already in place.

If the area where you removed drywall is near a window or door, it is important to test the seal between the door or window and the interior of the drywall. You can use a hose or spray bottle to check the seals on the side of the window or door. Seal off any areas that allow water through and remove any excess water. You can also treat the inside of the drywall with a mold-resistant paint or coating.

The last thing to do is replace the piece of drywall you removed. After applying your patch, use joint compound to seal the new edges so that moisture cannot get past the new drywall. Paint over the patch and joint compound, apply texture and sand it down. Then, filter the air using scrubbers and vacuums again.

Cleaning Moldy Areas Around Windows and Doors

It’s not uncommon to discover mold growing on window sills and around doors. While cleaning mold from a glass is relatively straightforward, addressing windowsills and doorjambs takes some technique.

Dampen the windowsill to keep spores from flying up while you are working. If the material is dry, you can apply disinfectant and scrub it down, following up with a HEPA filter vacuum. If the area is moist, do not use the vacuum.

When the mold is removed, check the seals at the edges of the sill. If mold has grown beneath the windowsill or door sill, you will need to pry the material out with a claw hammer or bar. The area behind the sill should be cleaned and disinfected, and then treated with a mold-resistant coating. Follow up using air scrubbers and a HEPA filter vacuum.

Cleaning or Removing Moldy Ducting

HVAC ducting is one of the more difficult areas to reach mold to clean. You will need to turn off your HVAC system to allow this ducting to be cleaned and use protective clothing and a respirator while cleaning.

Begin by knocking any loose dust into the open and vacuuming with a HEPA filter vacuum. You can use a spray bottle to apply disinfectant to the inside of HVAC ducting and an extended brush, like a toilet brush, to scrub the inside.

Check any filters in the system for mold growth. If they are showing discoloration, smelling of mold or don’t pass a surface test, throw them away and replace with new filters. In heating systems, shut off the fan and furnace, and then disinfect and scrub down the air registers and grills.

In some situations, mold colonies can grow in hard-to-reach areas of your HVAC system, such as ducting within building walls. To replace this ducting, contact a professional HVAC company and inform them that you need new ducting run to replace material infected by mold.

Step 6: Place Air Movers and Air Scrubbers

With humidity reduced and contaminated materials removed, you can begin the process of evacuating any mold spores left in building air. This is where the air movers and HEPA air scrubbers come in.

Spread air movers evenly in the space where remediation is being performed. The number, as well as the type, of air movers you will need, depends on the type of flooring. See guidelines for the number of air movers to use for your flooring type below:

  • Non-porous and semi-porous flooring: At least one air mover per 400 to 500 square feet.
  • Direct-glue carpet installations: At least one air mover per 300 square feet of carpet area.
  • Stretch-in carpet: At least one air mover per 300 square feet of carpet area.

Set your air movers up in such a way that they circulate air around the room, supplying airflow directly across wet surfaces or areas of contamination. Ensure air movers are placed at least six inches away from walls or other structures to allow for proper airflow.

In large open spaces, deploy one air mover for every 10 to 16 linear feet of wall. Airflow from blowers placed along walls should point in the same direction. Adjust the angle of the air outlet to between 15 and 45 degrees.

Air scrubbers should also be deployed at this time to remove airborne contaminants. To the mold removal process move along as quickly as possible make sure all filters are in good condition and have been replaced since the last remediation job to prevent contamination.

Scrubber effectiveness is measured in air changes per hour (ACH). One ACH is achieved when the air volume of a space can be fully filtered in one hour. To satisfy mold remediation requirements, a minimum ACH of 6 is recommended.

To find out how many scrubbers you need to use, take the cubic footage of the space and multiply it by six to determine how many cubic feet per minute of air you need to move to meet the 6 ACH requirement. Divide the air volume by 6 to get your target in CFM. Aer Industries offers scrubbers that can deliver up to 500 CFM, so you would use six of these air scrubbers for a 500-cubic foot room, for example.

Step 7: Thoroughly Examine the Building and Check for Cross-Contamination

Any time a mold outbreak is discovered, it’s important to consider all other locations mold could also potentially grow. That includes when removing old materials that mold has grown on. If you are stripping sheetrock, be mindful of potential moisture risks that could lead to future mold blooms. Examine the wood and insulation in the building to make sure that has not been contaminated as well.

If there is HVAC ducting or piping that intersects the area where remediation work is being done, these materials should be inspected, too. Mold is particularly fond of ducting where moisture levels can peak, as well as the insulation around it. Perform an air test inside of any ducting that is exposed when removing old wall coverings to ensure more mold colonies have not developed inside of the HVAC system.

Step 8: Replacing Old Materials

When your follow-up tests indicate that the contamination level in the area has receded and the area has been cleared by any other necessary agencies you can remove all the barriers and begin replacing any materials or furniture that had to be disposed of.

It is important that if you are replacing wall coverings, you avoid providing more food for additional mold colonies to break out.

In areas of extreme contamination, you may be required to use ducting to direct air out of the building. This ducting should never be re-used, and it should always be vented from the building through a sealed exhaust port.

As a follow-up in areas where you know high levels of moisture will be present, you can apply mold-resistant coatings such as sealers and primers. After installing new drywall, apply a layer of mold-resistant coating or primer. It may also be a good idea to recommend that your client purchase a dehumidifier to keep in the space permanently – such as a damp basement – if you believe that moisture may cause mold issues in the future.

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