The Effectiveness of Ozone Generators on Mold, Mycotoxins, Fragrance, and Smoke
Ozone kills and denatures mold on surfaces, and breaks down many VOCs and odors such as perfume. It can also remediate smoke smell in certain materials.
For those who prefer a video format, I have explained the process of a shock treatment and the risks in this video.
This post contains affiliate links to relevant products that I use and recommend. Upon purchase, I earn a small commission at no extra cost to you.
Please take full responsibility for your safety when using ozone. Make sure you read and understand all the precautions in this post. Full disclaimer is here.
For individual help with using ozone safely for your application, you can schedule a consultation with me here.
Does Ozone Denature Mold and Mycotoxins?
Some say that ozone kills mold spores but does not denature the toxins (EHC).
These two studies show it can denature the toxins.
Based on these two studies (that use very very high amounts of ozone), and the experience of me and those extremely sensitive to mycotoxins, I do think it is accurate to say ozone actually kills and denatures mold.
It can still be a good idea to HEPA vacuum after ozonating to clean up dead spores.
A shock treatment is either a very high doses for shorter amounts of time or very long treatments (from 24 hours to 48 hours). You really have to experiment if you want to denature mold and see what works for you, and be prepared for byproducts (discussed more below).
The main drawback is the dose of ozone needed to denature mold also breaks down and oxidizes many other materials.
You should never be in the room with any device that is producing ozone for any amount of time. Read ALL the safety precautions in this post.
Which Ozone Generator to Use
I started with the Jenesco Ozone Generator with an output of 100-2100 mg. This is a high-quality unit with a timer and dosage control.
I liked this unit because it’s well made and, the timer settings and dosage control setting were useful.
This one comes in around $400
I have the little Airtherial 5000 mg one (pictured left) this is the lowest cost one I have seen.
If you are doing a shock treatment for mold you need one with a hold setting like this one.
If you are using it at low amounts for fragrance you will only need the basic timer.
You cannot control the dosage with these little inexpensive ones, but you can find them for under $100 on Amazon.
For only a little more than a hundred, you can buy this Ivation model which can dial down the dose from 6000 mg to 500 mg.
This is what I would use for going after fragrance and smoke as well as cleaning product residue.
You don’t want a high dose for these applications, start as low as possible. You should still be out of the space at low doses.
Results with Offgassing, Mold, Fragrance, Smoke
Using Ozone on Offgassing
- Chemical smell in Camplite (metal) trailer reduced after a few treatments.
- Glue smell reduced in brand new metal cargo trailer (this seems to work really well on the new glue smell in basic trailers).
- I would not use this is a new house or conventional trailer (that is full of plastics and upholstery) to reduce offgassing, it’s too risky and does not work that well.
Using Ozone to Break Down Mold
- Mold remediated in an all-metal trailer after 48 hours of a high dose.
- I also had a mold problem in another house I was living in. After the mold was remediated I was still very sick – throat swelling, extreme POTs and terrible insomnia. I then ozonated each room for 24 hours with the machine and was able to come back without any symptoms. I removed all the fabric and cushions from the area before ozonating and there were no adverse chemical reactions with the wood or anything else in the house.
- Dozens of folks extremely sensitive to mold have had success with long shock treatments which allowed them to renter cars, trailers, and homes.
- I’ve used it 4 times now in post remediations with a 24-hour shock treatment. I feel certain this denatures mycotoxins. I have also done 48 hr shock treatments in metal trailers that were very effective. (I let in oxygen during that time).
- However one of these times the 24-hour treatment created horrible byproducts in a wooden house. Even after excessive airing out, I got extremely sick. I overdid the ozone or did not have enough oxygen coming in. Big risk here. It was a long time before I could go in that house again.
- Some people found it useful to shock a room or tent and to “flash” belongings before any mold toxins could take hold.
Using Ozone to Eliminate Fragrance, Smoke and Funky Smells
- Smell removed from funky smelling fabric (towel that had a smell that washing would not remove).
- BUT: gave some fabrics like wool and cotton a strange smell after doing an intense 24 treatment.
- Ozone can help a lot with fragrance in a car or house as well as smoke smell. Car dealerships use ozone but not super high amounts of for long amounts of time. This works best if the fragrance wasn’t used over time, it’s not deeply imbedded. If deeply imbedded this is unlikely to work.
- This is very useful if the fragrance and especillay smoke smell are your big concerns. Go low and slow on fragrance, cleaning product residue and smoke until you start to see a difference.
- To remove odors the time needed for treatment is much less than the shock treatment for mold. This will reduce a lot of the risks. Car detailers run ozone for 15 min to 2 hours, typically, or until they can remove the smoke or other problematic odor.
You have to be sure you are using it safely and understand the limitations.
Do not be in the same room as ozone gas, ever, for any amount of time and make sure you understand the risks of oxidization of materials.
How to Use Ozone Safely
- Ozone is a very toxic gas.
- People and pets should not be in the building when an ozone machine is on. Do not even take one whiff of it. Make sure you have a plan to turn it on and off while holding your breath. Ideally, turn it off without entering the room (through the electrical panel or extension cord). It clings to your clothes even if you hold your breath and walk through – this is not safe.
- Ozone can be harmful from 100 ft away or more if it’s a high dose, it can harm others in the area including neighbors. Clear 200 ft in every direction before a high dose.
- Ozone needs to be 5-10 x above safe levels for humans to impact bacteria and mold (Pinto). You cannot treat mold and be near it.
- The place should be aired out for 25 hours minimum after using ozone to make sure that the gas is not inhaled. Ozone is unstable and will dissipate, but it does not dissipate as fast in a closed space with no airflow. If other VOCs form (see below) then it is necessary to air out the place for a while.
- The half-life of ozone is 40 min-25 hours. If byproducts have been created then give it a few days at least. Make sure there are tonnes of open windows for the air out.
- One reason government health sites do not recommend the machines is the shock treatment used to kill mold toxins is a very harmful level if inhaled (deadly if you stay in there). Even the low levels recommended as safe by some manufacturers is probably harmful to anyone sensitive to toxins (certainly it is harmful to me). So there is a huge risk if someone does not know how to use it safely. It’s also difficult to recommend in most houses because of the negative reactions outlined below. In many conventional houses, it might not be possible to avoid all those secondary reactions with materials.
Limitations of Ozone
- Ozone cannot remove carbon monoxide or formaldehyde (EPA).
- It cannot get into porous materials to remove mold or chemicals (EPA). My experience suggests that it does denature mold that is near the surface of porous materials. I don’t think it goes very deep.
- It will not help with chlorinated hydrocarbons (vinyl, plastics etc) (EHC) nor phthalates (Arlene Blum)
- May not work on clothes and shoes (Pinto). My experience is that there is a bad reaction with any fabric in high amounts. But lots of folks have had success remediating clothing and shoes including leather shoes. Though not all types of leather will hold up the same and some rubbers in shoes will eventually break down.
Negative Reactions and Byproducts of Ozone – What Can go Wrong!
Ozone reacts negatively with some compounds creating more VOCs. Some of the substances it reacts to are:
- New carpets (EPA)
- Active tobacco smoke (EPA)
- Terpenes (to form formaldehyde) (CDH)
- Styrene (EHC)
- Floor finish that contains pinine (Pinto)
- Ceiling tiles (from a client of mine)
- Old carpet (from a client of mine)
- Fabrics (from my experience)
- Wallpaper (from a client)
I have found there is a negative byproduct left with almost every porous material if you do this in high enough doses for long enough. Ozone oxidizes everything and this leaves an odor behind that can be harmful.
High doses of ozone used to really clear out mold toxins will also degrade or harm certain materials such as:
- Plants can die
- Natural latex/natural rubber is extremely vulnerable to break down.
- Styrene-butadiene rubber (SBR) is vulnerable (tires, many shoes, some gaskets, liquid waterproofing in basements, parts of electronics like in speakers, in lithium-ion batteries, and gasketed-plate heat exchangers).
- Nitrile rubber will break down easily (some rubbers are fairly resistant).
- Some Plastics, see these two lists of how vulnerable different types of plastic are.
- Fabric
- All types of nylon are extremely vulnerable to break down.
- Some artwork
- Steel will rust
This is not a comprehensive list, there may be more household materials that contain these components. And many other materials have not been put to the test.
I have done many high dose (shock treatment) ozone treatments and not broken down any coatings on electrical wires. Most wires are coated with PVC which is fairly resistant to breakdown from ozone. It will eventually be damaged by ozone.
Though if you have electrical lines coated in a different type of plastic or rubber it could break down and become dangerous. I haven’t’ seen this happen, but it’s possible. Please double-check the types of wiring you have. There may also be SBR in electronics, which is much more vulnerable.
Folks do ozonate electronics with success. It could be risky if you don’t know what plastics are in it, there is a risk of breaking down electrical component leading to electrical shock.
These eight plastics have more resistance to ozone.
I have seen Taylor guitars remediated with success.
How to do an Ozone Shock Treatment
For a shock treatment, remove everything fabric or wrap them in plastic, this includes mattresses.
Remove plants, pets, and artwork that is not behind glass. Tape up electrical outlets. Remove all electronics. Make sure you have everything you need before turning the machine on.
Hold your breath while turning it on and while turning it off (or use an extension cord or cut it from the breakers. Air out the place with fresh air for 25 hours. This is based on my experiences.
Make sure you research if this is safe for you and worth the risk. Understand why the EPA does not recommend it. It is too easy to do something wrong where you could breathe some in. Treat it like the deadly gas that it is.
If you are not sure if it will react with your carpet, walls, ceiling then it is a last resort treatment.
I consider all shock treatments to be a last resort.
You can also test a low dose first to see if any weird smells form.
Make sure it is dosed correctly for the space and if running it for 24 hours it needs an oxygen source.
Overdoing it can make your place intolerable. I recently had a bad experience where I overdid it with the ozone, it took a month to be able to go back in.
How to Dose Ozone
I generally use 3500 mg/hr in a single medium-sized or large room for a shock treatment. A shock treatment which is what kills and usually denatures the mold is usually 1000 milligrams per hour (mg/h) per 100 sq feet (at 70 degrees with relative humidity at or below 20%).
The level you are aiming for is 6 to 10 parts per million. Many people shock for 1-3 hours but those of us super sensitive tend to keep going until the substance is denatured. I have gone as high as 5000 and 7000 mg/hr in a very small trailer for 24 – 48 hours.
The machines I like are the Jenesco Ozone Generator with an output of 100-2100 mg. And the little 5000 mg ones on Amazon that are low cost with a “hold” setting.
Sources:
- EPA: www.epa.gov/iaq/pubs/ozonegen.html
- CDA: www.ct.gov/dph/lib/dph/environmental_health/eoha/pdf/ozone_generator_fact_sheet.pd
- EHC: www.environmentalhealth.ca/summer96ozone.html
- Michael Pinto: www.moldsensitized.com/ozone-generators-and-interior-mold-remediation-a-recipe-for-disaster/
- Arlene Blum, Chemist: www.sixclasses.org
- CraftTech Industries: www.craftechind.com/top-8-ozone-safe-plastics/
- Ozone solutions: www.ozonesolutions.com/knowledge-center/ozone-compatible-materials.html
- Apple Rubber: www.applerubber.com/hot-topics-for-engineers/understanding-the-link-between-ozone-and-rubber-deterioration/
Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.
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Cam says
So what would you do for a car that has a slight smoke smell? Do I replace the headliner and carpet in the car? Ozone before they are replaced? I don’t see any nicotine stained but I know it is there in some way. not sure which is worse for my kids.
Corinne says
It depends on if you are sensitive to a slight smoke smell. I wouldn’t do anything personally. Ozone works well on smoke. There are more options in the post on remediating fragrance and smoke.
Aislinn says
Thank you for this post!
Do you have dosing guidelines for fragrance (cleaning supplies, air freshener, laundry products, etc)?
It’s helpful to know the approach for shock treatments for mold and I’m curious what guidelines you suggest for fragrance.
Thank you!
Diane l Parish says
Hello, Wanting to rid small basement room from musty mold smell. Purchased small ozone machine and will remove speakers,(due to rubber disintegration, I read), also plants. I think I”d like to plug up 1″ space under door that separates basement from upstairs? Shall I run for half hour, and when off, enter room ,holding breath open only window down there and 1 walkout door, then not reenter for 6 hours? It’s summer and very hot and muggy this week, don’t want to much heat in. Thank you for your site
Anna says
Hi there thank you for this post! O wanted to ask about how I could.ozone my.car from mold prior to moving out of my home to camp for.a short.time. I’m leaving everything but the car will be the one thing that will cause problems as it got soaked last year due to water being spiked through the carpet.and mold has since developed. I’m not.name to replace the car and really would like to try the ozone option and see how it fairs. Would you be able to recommend how long and what amount would be best to kill the mold spores in the car? You mentioned short shock treatments and also longer times of having it run and I’m wondering which would be best for a car with mold and at what dose. Thank you! Also, are there any cheaper machines that to my a timer rather than having to hold your breath? I really.don’t like the idea of being exposed to even a little of it..but perhaps those machines are much more costly.
I appreciate your advice on this greatly
Clover Rayner says
When your home has been damaged by water, you may find the unpleasantness of mold. There are a few different ways to get rid of it, but does an ozone generator kill mold? While ozone generators may be an air purifier, ozone generators can kill mold spores.
Noel says
For fragrance smells, I know you recommend a low-dose for longer periods of time. But if you buy the 5000 MG device. can you just do smaller intervals of 5 to 10 minutes to achieve the lower dose? And if the space is airtight does that help?
Corinne says
Yes you can pulse it.
Laura says
Corinne,
I purchased a manufactured home and it reeks of air freshener. The previous owner had a pop-up air freshener in every vent as well as plug-ins. I’m having a heck of a time trying to get rid of the smell. I’ve tried vinegar, baking soda, bleach and am having the air-ducts and vents cleaned tomorrow. I think the smell is in the walls, but may be coming from the vents. I’m just not sure… am so frustrated. What would you recommend?
Mena says
I’m just another reader but I’d try hepa air purifiers, they all come with a charcoal filter for odors. I’d be interested if Corinne answers, maybe ozone is good for this too. And condolences, that sounds horrifying!
Lisa Correa says
Hi Corinne, thank you for sharing your knowledge regarding Ozone. You mentioned Heppa vacuuming after ozoning. Would the furniture also need to be wiped down as well? Thank you!
Corinne says
Yes I would wipe up spores since the spores remain after ozonating.
Jess says
I’m having issues with smells in my clothes. I have a few items I’m trying to save and did all the mold protocol steps of washing etc. But nothing worked. So, I’m considering ozone for this. Will it neutralize mycotoxins in the clothes and the MVOCs? I’m planning to put the clothes in a small shed and seal it up with the ozone machine. Do you think this will work?
Corinne says
It’s the MVOCs that stick to clothes if you have already washed them. It might help but ozone also reacts to fabric and so the oxidation odor might not be worth it. I tried it and didn’t do well with the oxidation of the clothing.
Jan says
We tried this with our clothes and it often worked, but not always. My husband used one of the outdoor storage bins you use on your patio to store your outdoor cushions (in our side yard away from the house) and put our ozone machine in that. We`d either use the timer function on the ozone machine, or set it to ‘on’ and unplug the extension cord when we wanted to turn it off. He put a couple of large tarps over the bin; without the tarp I got a headache even inside our house, but with the tarp on there seemed to be little or no ozone escaping – at least nothing that I noticed, and I’m sensitive to it.
Some fabrics did have a strong smell afterwards, but that did eventually go away if given enough time (a few weeks hanging on the clothesline in the wind). But it was better not to have those items for a few weeks than have to throw them out. However, some fabrics – especially anything that had mothball smell – just couldn’t be remediated. I imagine with enough treatment that might have been possible too, but for us it wasn’t worth it at that point.
We purchased an ozone generator after an experience where I reacted violently to a coat that had been exposed to a particularly bad mold toxin. We had it dry-cleaned (using non-toxic cleaners) and that didn’t help at all and I still reacted violently. So we made the choice to have it ozone treated (which cost more than the cost of the coat) just to see if that was a viable approach. After the ozone treatment I could wear the coat with no problems at all – no reaction. So we made the decision to purchase an ozone generator (and learn how to use it safely), and we’re glad we did. It’s not a miracle machine, but it certainly helps in some situations.
This website has been a great help to us – thank you.
Corinne says
Thank you for sharing
Nancy Vakeva says
Washing with Decon 30, made by Benefect, might work. My mold remediator recommended 1 oz per load, but I’ve used way more. It seems to help.
Faith says
I found a company online that sells nontoxic anti mold products including a product that can be added to laundry load that gets rid of moldy odor on clothing. I haven’t used it but good reviews
https://microbalancehealthproducts.com/all-products/
Corinne says
Not convinced about EC3 though might help a little with superficial cleaning.
Henriette says
What about ozone for a musty crawl space under an old home? I have fogged it a few times but that only helps for a little while. Home is from the 30s and i think there is only wood, dirt and pipes – both cast iron and plastic..
Corinne says
The crawl still has to be properly encapsulated at a minimum. You may be able to improve it by using ozone after it’s properly fixed and remediated.
Kelly Couch says
We live in RV. Found mold. (We have been through this before in houses and been treating mold for years) argh. Ripping out the damage remediation etc. . Living somewhere else. Was going to drop our Most important school books and some clothes and shoes etc into a Big Tupperware bin and drop the small portable Airthereal in the bin and run for 2 hours. Helpful or pointless for mycotoxins?
Corinne says
Shoes could easily be damaged. Wether it will help with 2 hours time, there is not enough data on it. I would say probably not. Though some have found benefits in short time at high concentration. It will not stay in a box though so you should not do that while being in the same house as this box.
Dan Coleman says
Hi Corinne,
We have a walk-in closet in our apartment that has a musty smell we are trying to get out. So far, we have tried one 2-hour shock treatment with our small ozone generator. To keep the ozone inside the closet, we sealed the doors with plastic sheeting and duct tape. We ran an extension cord so that we could turn the generator on and off without breaking the seal.
We also placed a fan and air purifier in the closet, so we could turn them on from outside once the generator finished running. Given enough time, do you think the airflow created by these devices would break down the lingering ozone, without introducing fresh oxygen? We need to keep trying to treat the closet, but we have nowhere to stay while the apartment airs out properly. Any advice would be greatly appreciated!
Corinne says
The ozone won’t be contained by the plastic here, the closet is not airtight on the inside. It will break down slower without adding outside air to air it out.
Bonnie DelGatto says
I have become overly sensitized to the ozone & I don’t know how to fix it.
I had mold. my sheet rock was replaced, whole house repainted, all furniture gone, & then………..I overdid the ozone. I stayed in the house for a few days after without opening windows because (stupidly) I was having work done OUTSIDE. By the time I realized what was happening it was too late. I’ve since aired out the house & sanitized it but I’m extremely sensitive anytime I’m inside. It feels to me as if there’s not enuf oxygen. My veins feel as if they’re swelling, my legs feel weak, my face feels swollen & I’m afraid to sleep for fear of not waking up. When I go back outside my chest begins to hurt. I’m 45 yrs old. Doctors can’t figure out what’s wrong with me. I don’t want to sell my house but I don’t know how to fix me. Any ideas, please?????
Corinne says
Give it a month and then re-asses.
Ivan C says
Hi Bonnie,
I just finished reading a book called Breath, by James Nestor.
Its about the benefits of breathing exercises. It may at least help your anxiety/fear.
Carissa says
I bought a car that had one of those tree air freshener in it and I’ve steam cleaned and vacuumed, used vinegar, baking soda, etc. Can’t seem to get it out of the dashboard plastics. Would an ozone generator help for this or would it make it worse? I keep having asthma attacks.
Will the air freshener stop off gassing eventually as it has been removed? None of the upholstery smells like it.
Thank you
Corinne says
Yes it should help but it might leave an odor from its reaction with the upholstery
Jessica Wald says
If ozone causes a bi-product with fabrics/carpets…then how is this safe to use in cars? I have purchased the new cordless mini arethereal ozone machine and done 3-4 (15min) shock treatments in my car followed by hepa vacuuming and wiling down with EC3. I seem to have trouble being in the car still, maybe its not mold buy the reaction with the carpeting on the floors of the car and the fabric on the ceiling fo the vehicle? Is there any way of knowing or dealing with this other then time?
Corinne says
The fabric reaction is one I can smell quite easily. 15 min is very short to cause a breakdown. I was doing 24 hour very high dose treatments. Even then, the fabric odor will die down.
Obed says
How long the effect of ozone gas as disinfectant remain in a 20 SQ meter room if this room remain closed.
Corinne says
Do you mean how long does the gas linger after? There is a link there to how long it takes to break down based on humidity and temperature. Ozone doesn’t stay in one room though, it will escape from one room. I air it out with lot of air movement for 24 hours before going to check on the oxidation left behind.
Augsnod says
My ozone generator has been a life-saver for me. I've lost nearly everything due to MCS and finding a safe home was vital, along with all the products that I have to live with. I've used my generator to make so many things safe, including my home itself, plastic products from China, fabrics with laundry chemicals, and even new clothing that was unwearable. The key to successful treatments – for me – is short duration usage followed by adequate ventillation. I usually do 15 minute treatments followed by hours of settling time. I'll get faint whiffs of ozone, but it goes away pretty quickly. I've had some very difficult situations that I've done repeated treatments of about an hour, but that's the longest that I've used it.
For those interested: I bought a bare-bones generator that is very inexpensive. The company has useful information for using these machines, and one of the most useful pages is the one on mold: instead of advocating that people purchase their product for mold, they advise against it in favor of professional remediation.
https://www.foreverozone.com/pages/ozone-for-mold-issues
Corinne says
I have one of their machines as well. It seems they are not selling them anymore and I was not even able to get a plate order it (though of course you can buy those plates anywhere). They are absolutely the most bang for your buck but I cannot promote a machine with so few safety controls on it. I tried to ask them some questions about the construction bc there is a possibility in certain conditions, with a broken plate, depending on how it is made that can delivery a deadly shock. It has no cover on it and does not look like it has proper safety measures.
Hasselhoff says
I think I overdid it in a bathroom. I had kept the door shut while running an ozone machine for 10hrs. Got rid of the a odor issue we were having, but left a very strong chemical-like odor afterwards. It's been 4+ months, and after constant airing out it still smells acrid. I can't stand going in there and keep the door shut.
Wondering if your situation has improved with time?
Thanks!
Corinne says
It did improve but I never went back to live in the house that I ruined with ozone. So I'm not sure how long it would take to go away. A lot depends on what it reacted to and if you are super sensitised to it now.
Hasselhoff says
Thanks for getting back so quickly. Sorry to hear you are not able to go back.
Thinking I've just become hyper sensitized. There's some days I feel like that 'smell' is everywhere. Very strange. Other people notice a faint 'off' smell, but have no problem with it. It might have reacted with the paint or tile adhesive; like a sweat plastic odor. Thinking to just refinish the entire bathroom now.
Sounds like you generally had success with ozone treatments. Do you continue using it?
jackieM says
Hil, I totally over ozoned my car,. A friend gave me the machine and said to leave it for a few days. I’ve been trying everything and airing it out as much as I can. It’s been about a month and it’s stilll hard to drive in my car without the windows open.
What can I do? I’m worring I am damaging my lungs.
Any suggestions? besides selling the car?L l
l
Corinne says
A few days is really long especially if it was oversized for a car or didn’t have enough oxygen. I don’t know anything but time for that. I have over ozoned my truck with 24 hours and for me it needed a month but was not prefect even then. It did recover.
Karen says
I do believe the dealer we purchased our car from over ozoned it. It’s been several days and I still get Asthma symptoms from the car. Would running an air purifier like an Austin clean it up and make it tolerable for me?
kim says
If there is a smell in fabrics after using ozone machine for 24 hours, is there any way to get rid of it? And how might go go about getting rid of any residual smell in the house after 24 hours?
Thank you!
Tatiana Irvine says
How do you protect the ozone machine itself from becoming contaminated (with mold/mycotoxins)…and then cross-contaminating a different space?
Corinne says
The ozone at high doses breaks down the mycotoxins so I'm not sure how the machine would become contaminated.
8905 says
In what negative ways exactly will an ozone shock treatment affect older carpeting?
Corinne says
It creates a bad smell.
8905 says
In what negative ways exactly will an ozone shock treatment affect older carpeting?
Corinne says
It reacts with all cloth materials to form a biproduct. It has a very weird smell and hard to describe.
Sarah says
Will the smell that is a byproduct of old carpet go away/diminish?
Corinne says
The byproduct of ozone and old carpet, yes in my experience it does go away.
Dat Hoang Tien says
Nice post!
Same Day Inspection says
What is a good home mixture to remove blackmold? I believe a mixture of bleach and soap and water works, but I'm not sure.
insulation inspection
Wild Swan says
We physically remove mold in the properties we purchase. If a wall shows mold on the interior of the drywall, we take out the drywall to examine the studs. The studs almost always show mold, in which case we remove the wall down to the wall plate to reach the concrete foundation wall. Bleach does not reach the roots of the mold, the EPA has essentially admitted it doesn't work for cleanup, after many years of advocating it.