How to Remediate Mold

Before we talk about how to remediate mold (clean up, treat for), I must give you a warning about handling mold, should you be contemplating doing your own remediation. Listen carefully!

Warning: A very common mold in most all these scenarios is Aspergillus, which can grow in human tissue (sinuses, lungs, etc.). Wear a P100 or N95 respirator when handling mold (and fiberglass). Wear goggles when working above your head. Have no exposed open sores. Put up containment so that mold particulates aren’t spread beyond the work area. Read the Cutting Edge tab before you start work!!!

Briefly, what you will learn at the Cutting Edge tab is that demolition and cleaning can release many tiny microparticles that can be inflammagens (start an inflammatory cascade in a susceptible person). These tiny microparticles do not settle out in dust. They remain as suspended particles in room air. In other words, a “good” remediation job can be done according to industry standards, and,in some ways, the area can be left unhealthy. There is a specialized fogging and wipe/down method that can remove these microparticles. This is talked about in the Cutting Edge tab.

OK, I got that out of my system. Now let’s move on with the topic of how to remediate mold. So you know you have mold now, and perhaps you are contemplating getting someone in (a professional mold remediator?) to deal with it. Where do you go from here? How do you find a good remediator?

The purpose of the information in this tab is to ARM YOU AGAINST THE MOLD INDUSTRY. There are plenty of ignorant, incompetent, inadequately trained, greedy remediators out there. Some charmers, alas, turn into bullies when their work is questioned. Some of my esteemed remediator colleagues know exactly what I’m talking about and would agree with me. It takes work and commitment to be a professional in this field. And, if you take a look at the Cutting Edge tab, you’ll see information that even the best of the professionals may not be aware of…information that could impact on your health.

The other side of the coin is if you will be doing the work yourself, or have a local handyperson do the work, or your own contractor. How can you remediate mold safely for all concerned, including the health of your home?

What I’m asking myself

  • How can I convey to the reader how to find his or her way through the pitfalls in the mold industry, both for inspection and remediation? We talked about do-it-yourself inspection, but I didn’t mention bringing in a mold inspector to check your home.Hmmm, why didn’t I give you suggestions for choosing a mold inspector? I just realized that I didn’t do that. Here’s why: because almost no one works on-site with a microscope. How can an inspector identify where mold growth is when the growth is not visible to the naked eye? How can inspector draw up guidelines for cleaning up mold when he can’t identify where the mold is that needs to be cleaned up?Let me tell you what the schools teach the inspector to do, and you will see why a lot of mold is being missed. Mold industry guidelines essentially say that one spore trap air sample should be taken on each level of the house (maybe excluding the attic) and outside, and that the inspector should take a tape or swab sample of anything that looks like visible mold. And that’s it for sampling, except maybe for working with a moisture meter.(Some inspectors are nevertheless quite knowledgeable and experienced. They know construction and do a good job, within the limits of a visual inspection.) I believe, though, that if they got used to using a microscope, their eyes would be opened to its usefulness. A microscope is my best tool.I wouldn’t know how to interpret mold at a house with the flimsy data of the mold industry.  At my average inspection, between air and tape samples, I’m taking 40-60 samples. As I say to my clients, “This may be overkill, but better too many samples than too few.” I’ve never had a client disagree with that one.You see, the mold industry is built on lawsuits, that is, protecting yourself from getting into one. Every sample goes to a lab. Numbers of samples are limited, or the lab fees would be too high. The inspector feels that nothing can come back to haunt him if he has followed industry standards and the lab results are good.
  • In contrast, my inspections are health-oriented. My clients don’t want a string a good lab results to paper their walls with. They are trusting me to find the mold, no matter how it’s done or what the lab results show. Air samples may miss the mold, which maybe wasn’t giving off spores at the time of testing or which may be hidden in wall cavities or in rooms away from the test areas. Many inspectors set up tripods and test 3′ up in the air. Not me. I do aggressive testing, placing the collector on the floor and stirring up dust near the collector. If spores have drifted down into settled dust, I want to find them.
  • What’s the secret to a successful experience with a mold inspector? It’s simple. You do the inspection first, before the inspector comes. Then, if he misses something, you can point him in the right direction.
  • If any inspector reading this is doing, or willing to learn, this type of in-depth inspection, please contact me – 888-735-9649.

Let’s get to work with learning how to remediate mold!

I’m going to give you an overview of common fungi (molds), followed by tips for choosing a remediation firm.

Here’s what you need to know about common molds

Tip: There is so much we do not know about mold. The science is in its infancy and is very complex. The bottom line is: There should be no mold growth in your home. Just get rid of it (safely and effectively). It does not need to be killed before it’s gone. If it’s gone, it’s gone. Protect vulnerable surfaces from mold growth by encapsulation (sealant), moisture control, proper storage, and good housekeeping with a true-HEPA vacuum cleaner and damp-dusting. Minimize clutter. In-depth spring and fall cleaning are good practices.

Common molds by types:

Alternaria: Dark; can grow in leak areas and areas of condensation; can grow under faulty shower installations and on drywall; associated with asthmatic and other symptoms.

Aspergillus and Penicillium (Asp/Pen): Green, white; can grow just from elevated relative humidity and condensation; very common in basements and at leaks (wall cavities, ceiling cavities); can grow on furniture in damp areas; linked with many health issues; spores become airborne easily; can grow in sinus and lung tissue and migrate through the body.

Chaetomium: Sometimes seen on the bottoms of ceiling beams in the basement and on the bottoms of rafters in the attic as black splotches. These are often of little consequence, left over from the time of construction, dead mold – but should be removed before a house is put on the market. Spray with Concrobium mold stain remover. Even dead mold particulates can be allergenic, so wear a P100 or N95 respirator whenever dealing with mold.

Cladosporium: Black; grows at areas of condensation (window sills, AC vent covers, AC systems, window AC units, shower ceilings, shower curtains); most common outdoor mold; spores don’t become airborne that easily indoors and so the mold can be wiped off; allergenic to some people, plus linked with other health issues. Cladosporium contains melanin to protect it from UV-C. This black stain may remain after wiping off the mold.

Stachybotrys: Black, needs prolonged wetness from water leaks or flooding to grow, likes drywall, spores do not become airborne as easily as Asp-Pen; linked with pulmonary hemorrhages in infants under 8 months and neurological damage, etc., in all ages.

Trichoderma – green (sometimes seen on basement subflooring by plumbing pipe access holes; can have similar toxins to Stachybotrys).

Ulocladium – black, grows in leak areas, sometimes on attic sheathing

Common molds by location

  • Attics – Cladosporium, Ulocladium, Chaetomium
  • Wall/ceiling cavity leak areas – Asp-Pen, Stachybotrys
  • AC systems – Cladosporium, Asp-Pen
  • Basements – Asp-Pen, Cladosporium, Trichoderma, Chaetomium

Helpful points of discussion with remediators

  • 1st question for remediator: What products will be used? Come to an agreement with the remediator.
    • Tip: There are 2 classes of products – cleaning products and encapsulants. Cleaning products are for cleaning off mold. Cleaning products don’t to kill the mold, just get rid of it. Cleaning products are temporary, because mold could grow back.Encapsulants are more permanent. Encapsulants can be toxic (pesticides) or least toxic (has lime to kill mold).Many remediators are more comfortable using products with pesticides (also known as mildewcides and biocides). ‘Cide’ means to kill. They want the mold killed dead so that they don’t get any later complaints about their work. Unfortunately, what kills mold harms us, too, because we are made of the same things as mold. We want effective products used, but not products that may harm us afterwards. We don’t want the cure to be worse than the mold.Question: What about green products?Answer: In my experience, Borax works fine in wiping down studs and sill plates in the basement. Green cleaning products may be ok, but my $3 box of Borax does it for me. The problem with green products is that the remediator might not realize that an encapsulant should probably be used after cleaning, or mold could grow back. (I’m hedging with my words, because situations differ. If there is no wood that had mold growth on it, it doesn’t need an encapsulant.)
    • Borax is a least toxic and effective cleaner. (1 cup per gallon of water, or sprinkle some powder on a damp sponge, available in the laundry aisle of a supermarket.)
    • Benefect (available on-line is an EPA-registered sanitizer which can be used for cleaning and in areas of sewage contamination). Never fog with Benefect, because the thymol in it can be harmful to lung tissue when fogged.
    • Caliwel is an EPA-registered biocide (kills mold) and biostat (encapsulant that seals and protects the surface), available from 212-317-0100 or, Caliwel). Caliwel can be ordered on-line from Home Depot.
    • Other EPA-registered encapsulants likely contain pesticides (also known as mildewcides and biocides). If the label has an EPA registration number, it contains a pesticide.
    • I was recently introduced to the Concrobium mold stain remover spray. This contains acids, and some people may react adversely. I have no experience or feedback from clients on the use of this product yet. The alternative would be to sand off residual stains, and then encapsulate.
  • 2nd question for remediators: “Will large areas (ceiling joists and subflooring; walls and ceilings) be wiped off or not? National guidelines call for starting with a clean surface, so your remediator may not be comfortable going a different direction. On the other hand, the Caliwel manufacturer says that a moderate amount of mold can just be painted over (spray-painted). If Caliwel is sprayed and subsequently protects the surface, then sanding off buried hyphae (like “roots”) would be unnecessary, saving on labor costs. If there are stains, spray with the Concrobium mold stain remover first.Architectural Caliwel is paint-like. Industrial Caliwel has more active ingredient and hence is a bit stronger, but is opaque. For more information, go to Caliwel has a strong paint smell until it dries, so cross-ventilation during spraying is recommended. Some chemically sensitive individuals may be more comfortable with just whitewash being used. Go on-line for a recipe.The tendency for contractors is to over-spray, using unnecessary product, sometimes twice as much as estimated. Only a thin coat is needed. Since Caliwel has a high pH (alkaline), a sprayer with a stainless steel nozzle must be used. Otherwise, the sprayer will clog up. I have no financial interest in this or any other product mentioned in this website.
  • 3rd question for the remediator: Will an encapsulant be used? Not all remediators feel this is necessary, but use of an encapsulant would be my recommendation if any wood remains that may have buried hyphae (“roots”). Protect cleaned surfaces from future growth – either from new spores or from re-growth of buried hyphae. Spraying on an encapsulant protects your remediation investment. I’ve seen areas without encapsulants where mold has grown back.Tip: Don’t forget to check the Better Business Bureau and any other places where complaints may be listed. A client just last night told me that she found the same complaints listed when she checked (after the fact, regretfully) as she experienced at her remediation project. “I don’t want those people back in my house,” she said.

What to anticipate from a remediation job

I’m going to give you a list of possible jobs (different scenarios) that you might need at your home – and what to expect from a professional remediator. You or your handyperson can also follow these steps – but I cannot assume any responsibility for your work. So if you have any questions, or if you are prone to respiratory issues, or if someone who is ill lives at your home, or if you have a baby at the house …consider hiring a professional remediator.

Scenario 1: A plumbing or roof leak (mold in wall or ceiling cavity or sink cavity)

Remediation guidelines – what to expect

Workers must wear personal protection (P100 or N95 respirator, preferably with nostril valve, etc.). If working overhead, wear goggles. OSHA requires a worker using a respirator to have health clearance first from a physician, because of the added resistance to breathing. You can get the health questionnaire at and then search on “respirator health questionnaire.”

  • Protect the clean areas of the house by setting up containment.
  • As needed, set up an air scrubber or negative air machine.
  • Using plastic sheeting, seal off supply vents and returns in the vicinity of the work space.
  • Remove contaminated drywall and insulation, etc., and place in plastic bags for proper disposal.
  • HEPA-vacuum in the cavity.
  • Using a strong flashlight, examine for signs of further water penetration or discoloration.
  • Make sure there has been sufficient demolition – better too much than too little. Examine nearby surfaces, including drywall, flooring, ceiling material, etc. Trace the path of water to find the mold.
    If needed, send me tape samples from peripheral areas to confirm that sufficient removal of contaminated drywall, etc., has been done.
  • If materials that will remain (studs, sill plate, ceiling joists, and sheathing) have signs of mold growth or water-staining, HEPA-vacuum the growth and then wipe off with a little Borax sprinkled on a damp sponge or cloth.
  • Finish cleaning, and arrange for post-remediation testing as needed.
  • Apply two coats of encapsulant to wood surfaces that may have had mold growth or need to be protected.
  • Routine cleaning with a quality HEPA-vacuum cleaner and damp-dusting (or dusting with a microfiber cloth) will continue to reduce levels of stray spores and other mold particulates.
Scenario 2: Mold in a crawlspace

Remediation guidelines – what to expect

  • If there was insulation put between ceiling joists at the time of construction, the insulation may have protected the wood surfaces it covered from mold. Highest levels of mold are likely to be on the edges of the ceiling joists that are exposed to the air.
  • Concrete typically does not support the growth of mold. However, if moisture migration through the foundation wall has resulted in efflorescence (a deposit of minerals and dirt on the foundation wall), there may be some mold mixed in that efflorescence.  HEPA-vacuum, damp-wipe, and take steps to reduce moisture intrusion from outside.
  • Workers must wear personal protection (P100 or N95 respirator, preferably with nostril valve, goggles, gloves, and possibly a disposable suit) when working with both mold and fiberglass.
  • If the entry to the crawlspace is through the house or basement, take steps to contain the crawlspace work area and to minimize the risk of cross-contamination.
  • Remove insulation and bag for proper disposal.
  • Examine the subflooring for signs of water penetration and discoloration. If visible mold is present, HEPA-vacuum and wipe off with Borax sprinkled on a sponge or cloth.
  • Apply two coats of encapsulant to subflooring and ceiling joists.
  • Arrange for post-remediation testing if desired. Raw count levels of spores in crawlspaces may not be as low as in other areas because of cleaning limitations.


  • The more modern way of thinking about a crawlspace is to make it part of the house. That is, essentially set up plastic sheeting (like a swimming pool liner) to separate the crawlspace from the earth outside. Then a fan or dehumidifier would be placed in the crawlspace and it would be open to the interior, assuming there is an opening. Some crawlspaces are too shallow and too hard to get around in for any “swimming pool liner” to work.
  • A twist on this approach is to tape foam board insulation around the foundation walls of the crawlspace, cover a dirt floor with plastic sheeting taped to the insulation, and set up a fan to ricochet air around the crawlspace. (Make sure using uncovered foam board is not against your local fire code.)
  • The more old-fashioned (and maybe more practical) way of thinking about a crawlspace is to protect it from mold growth and to have adequate ventilation (vents can be shut in the winter). This approach costs a lot less, because you don’t need to run a dehumidifier. When wood is protected by an encapsulant, mold spores can come and go. Who cares, as long as they have nothing to feed on. Adding in insulation and setting up a fan near a corner to ricochet air around the crawlspace may be a good idea, to keep air moving.
Scenario 3: Mold in an almost inaccessible crawlspace
  • Sometimes the best you can do is to exhaust musty air. Figure out how to promote cross-ventilation. In the central states and New England, prevailing winds are from the northwest, so have a vent open at the northwest and place an exhaust fan in a window or vent in the southeast, to draw air through.
Scenario 4: Mold in an unfinished basement

Remediation guidelines – what to expect

  • Rule out the presence of other toxic materials, such as lead and asbestos. If present, they should be dealt with first. Old red paint on the slab could be lead paint. Old floor and ceiling tiles could contain asbestos, as could a cloth-like elbow on an old heating unit.
  • Protect the living areas of the house from cross-contamination. If there is an outside entrance to the basement, use that exclusively and seal off the door to the upstairs.
  • Set up air scrubber(s) and negative pressure.
  • Seal off vents or returns. If applicable, make sure sufficient oxygen is present for heating units… but the heating unit probably wouldn’t be on if ductwork is being sealed off.
  • Clean contents and move them to a clean area for storage.Tip: Here’s how to clean contents
    • Glass, metal, and plastic items can be washed or wiped off.
    • Soft items such as wicker, paper, cloth, and upholstered furniture may need to be placed in plastic bags or wrapped in plastic sheeting and discarded.
    • Furniture to be retained can have its unfinished surfaces HEPA-vacuumed and wiped down with Borax. If furniture is really moldy, it may not be salvageable. Sometimes wood surfaces are steamed by remediators.
    • Mold can grow more easily on soft wood such as pine than on hard wood such as oak, maple, and cherry. Mold grows more easily on unfinished surfaces than finished surfaces.
    • Change items stored in cardboard boxes to plastic boxes or plastic bags and bag and discard the boxes.
    • If there are items you especially value and do not wish to discard, confer with your remediator or give me a call.
    • With costly antiques or paintings, confer with a fine arts restoration company or a museum.
    • Some furniture can be preserved by cleaning and then encapsulating every square inch of unstained wood, including inner framing.
  • Continuing with the guidelines — If you have no other place to store cleaned items, they may need to be stored in the basement. If so, set up a temporary plastic room (containment area) and remediate that room first. Then move cleaned items to that area. Cleaned items may also be covered with drop cloths. Smaller items can be cleaned and transferred to plastic boxes for storage.
  • When the basement is cleared out, remove any fiberglass insulation and place in plastic bags for proper disposal. Be sure you have proper eye and lung protection on.
  • HEPA-vacuum as needed to prepare surfaces for encapsulation.
  • Apply two coats of encapsulant to every square inch of wood in the basement, including ceiling joists, subflooring, steps, backing of electric box, workbenches, and shelves. Apply encapsulant to surfaces not visible when standing in the basement, such as the surfaces of cross-bar support wood that face upwards and the underside of steps.
  • Complete the cleaning process. One standard of care in the industry is the “white glove test.” A white glove wiped on a surface should come up clean. Of course, in a basement, that is next to impossible – but it does indicate how thorough the cleaning process should be. Mold particulates settle into dust, so dust must be removed.
  • Arrange for post-remediation testing, to consist of spore trap testing (with raw count results for Aspergillus/Penicillium preferably in single digits) and a visual check.
  • If desired, apply a moisture retardant such as Thoroseal to foundation walls. Of course, take needed steps to reduce moisture intrusion into the basement. Protect your investment.
Scenario 5: Mold in a finished basement (that will have some removal of building materials or will be gutted)

Please see Scenario 4 regarding containment, negative pressure, and contents.

  • After contents are moved, remove carpeting and wrap for proper disposal.
  • Make a judgment call on how much of the finished walls and ceiling need to be removed. If the basement is damp, consider removing all. If the basement has been dry and there was a recent flood, maybe you can get away with removing the bottom 4’ of drywall and any insulation. If you caught the water quickly, maybe you could remove the bottom 2” of paneling and cover the gap with composite base molding later, after drying and encapsulating inside the opening. With older damp basements, maybe the basement should be gutted.Tip: Fiberglass insulation behind basement walls can retard the progress of mold spores upwards.Tip: Feel free to send me tape samples from remaining materials as needed to rule out additional growth. (fee)
  • Finish demolition as needed.
  • HEPA-vacuum in wall cavities.
  • Apply two coats of encapsulant.
  • Finish cleaning.
  • Arrange for post-remediation testing as desired.
Scenario 6: Attic mold
  • The scope of the job will determine the type of treatment.
    • For spot areas of discoloration, either wipe off with borax on a damp sponge, or spray with Concrobium mold stain remover.
    • For huge areas of discolored and deteriorated sheathing, the sheathing may have to be replaced when re-roofing. As a temporary stopgap measure, sheathing could be sprayed with two coats of Architectural Caliwel. Or, do nothing except improve cross ventilation. If gaseous toxins cannot immediately be addressed, they can be diluted. From a health standpoint, mold in the attic may not be a significant factor, as long as the attic is separated from living areas.
    • For substantial white or green fuzz that has grown where rafters meet sheathing, some sort of blasting technology may be needed – such as blasting dry ice to dislodge the mold and cause it to drop down into old insulation. Then the insulation would be removed and replaced. Review options with your remediator. Correct the conditions that caused this mold growth.
Scenario 7: Elevated levels of mold in living areas
  • If no sources of mold growth have been found in living areas, then treat this as a dust-removal project. In-depth spring and fall cleanings are good practices to follow. Make sure you have a quality HEPA vacuum cleaner. Damp-dust or use a microfiber cloth. If desired, get a room air purifier, such as the IQAir. Keep the premises shipshape, with a minimum of dust collectors. If possible, avoid carpeting. Carpeting traps allergens and can never be completely cleaned.
Scenario 8: Mold in HVAC systems (heating, ventilation, and air conditioning)
  • If your system has had a fiberglass filter, there is a good chance the system could use a cleaning. The preferred filter is a pleated media filter. Electrostatic and electronic cleaners are not recommended, both because they can lose efficiency as dust coats surfaces. With electronic cleaners, levels of AC electric fields are elevated throughout the house when the electronic cleaner runs, as demonstrated by an electrical engineering colleague with a frequency analyzer.

Tip: From a health perspective, the purpose of the filter is to protect the AC coils from dust and dirt. The coils are the site of condensation. If they are clean, there is no problem. If they are dirty, mold grows.

Tip: Before contracting with a service, read the EPA brochure on duct cleaning. Go to and search on “duct cleaning.”

Here are some cautions:

  • Some duct cleaning companies do just that, clean ductwork. Avoid them. You need a company that will clean the whole system, especially AC coils.
  • If the AC coils cannot be cleaned in place, they should be removed for cleaning. If they are old, just replace them. They are the most important part to be cleaned.
  • Flexduct (plastic tubular ductwork) cannot be adequately cleaned and should be replaced. The one exception is when the flexduct is not particularly dirty and then perhaps it can be air-puffed out. Discuss with the remediator or duct cleaner.
  • Avoid fogging with biocides. Just ask for mechanical cleaning, including vacuuming, puffing, and mechanical agitation. Regarding biocides, you may prove to be sensitive to these chemicals. Further, we do not know, after the active ingredient is gone, whether the residual compounds may serve as food for mold and bacteria.
Post remediation testing

Post-remediation testing is typically done after a professional remediation job. Not only do you want assurance that a good job was done, but the professional wants to be able to look back and say, “It was fine when I left.” Here are types of testing:

  • The most common type of testing is a visual examination plus spore trap sampling, where air samples are taken in the work area, a control area, and outside. These samples must be submitted to a microbiology laboratory for analysis. There are no standards for what is acceptable, but I look for single digits in the raw count for Aspergillus/Penicillium, except for attic and crawlspace results which may be higher because of cleaning challenges.
  • If a paper trail is not needed for legal purposes, I generally do culture plate testing, which can be studied in-house (and sent to a lab afterwards if needed). Depending on whether surfaces have been encapsulated yet or not, I may also do tape-testing. Once a surface has been encapsulated, it is not possible to tell how much mold was painted over.

Question: What are considered good results with post-remediation testing?

Answer: I look for single digits in raw counts for Aspergillus and Penicillium. However, each inspector is left to his or her own opinion on this. Some inspectors would accept higher counts than I would. Aspergillus and Penicillium spores are, for me, marker molds of how good a job has been done.

That said, there’s something you should be aware of. If a negative air machine has recently been shut off, spore counts could be artificially low. Wait a week or two and they might be higher. Most remediators don’t want to wait too long, because they don’t know “what you might have done wrong since they were there,” i.e., forgotten to run the dehumidifier, opened windows, etc.

What’s the solution? I do tape-testing to better the chances that sufficient demolition has been done. Plus, there’s the visual check of surfaces like the tops of hot water heaters to make sure dust removal has been thorough. I also touch a tape to the top surfaces of cross bar supports between ceiling joists in the basement to see if all surfaces have been cleaned – or just the ones the remediator figured the inspector would visually check.

Well, we are now at the end of this section. I remind you that the Cutting Edge information has relevance here.

More information on mold clean up can be found at my other two related sites:

To contact me, write to may at 


Now let’s move on to the Cutting Edge tab.

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