How to Find and Control Mold in a Home or Business

You may be wondering if your home or business has a mold problem. If you already know the building has a mold problem you’ll need to know how to get rid of it and keep it from ever returning. Mold thrives in moist and warm environments which means wet or humid areas are prime locations.

Mold along the floor board

In this article we’ll cover a number of topics, including:

In addition to health risks associated with some species of mold, the moist environment of mold’s habitat can cause bigger structural issues. Too much moisture in a home or building can cause wood to swell and warp (or even rot), causing a weakened home or structure. According to the U.S. Environmental Protection Agency, the best way to control mold growth is to control moisture.

What Is Mold?

Molds are fungi that thrive everywhere – both indoors and outdoors. They grow best in warm, damp, and humid conditions. When conditions are right, mold can even grow in areas where humidity is low, such as Arizona.

Molds reproduce by forming spores that are spread by air currents. Since mold spores are literally everywhere, there are no reliable and cost-effective means of eliminating them from human environments or creating a mold-free space. We can, however, limit mold growth by controlling the amount of moisture in our indoor environment.

Mold needs four things to grow:

  • Mold spores
  • Nutrients – any organic substance such as wood, paper, drywall
  • Moisture – water, condensation, or damp air (when the humidity is above 60%)
  • Appropriate temperatures – between 40 and 100 degrees

No one knows how many molds or species of fungi exist. Some estimates range from tens of thousands to upwards of 400,000, although less than 100,000 have been named.

There are approximately 1,000 types of mold found indoors across America. Less than 80 molds are suspected of causing some form of illness, and only a handful are considered toxic.

The common types of mold found indoors include:

  • Aspergillus and its subspecies (A. flavus, A. versicolor)
  • Cladosporium
  • Penicillium
  • Alternaria
  • Stachybotrys atra, also known as “black mold”

Mold often grows in places not readily visible. It can be found behind wallpaper or paneling, the top side of ceiling tiles, the back side of drywall, or the underside of carpets, carpet padding, or wood flooring.

Piping inside the walls may also be a source of mold growth since pipes often leak and cause moisture and condensation. Roofs, too, sometimes leak, and water collects inside walls and insulation.

Many Sources of Moisture Intrusion in the Home

Dampness by window
Indoor water leaks, broken pipes, water leaking from a clogged air conditioner drain pipe, a leaky roof, poorly sealed windows, basement flooding, steam from showers or cooking – these are some common conditions that allow moisture to become a problem in homes, apartments, schools, and the workplace.

Outside Sources

Many other conditions that can contribute to water intrusion and lead to mold proliferation, for instance, gutter downspouts or lawn sprinklers placed too close to an outside wall. They can cause water to seep straight into a basement or saturate a concrete foundation. Once the concrete becomes wet, moisture can wick into the home or building.

Construction Issues

Also, using polyethylene PVC piping instead of copper or galvanized piping (the PVC pipes can be punctured easily by nails or staples), improperly sealed bathtub drains, improperly sealed sinks and garbage disposals, or even the installation of particle board after it has been rained on during construction – all of these issues can cause mold growth.

Water Vapor

When relative humidity indoors increases to 60 percent or more, building materials and furnishings absorb the moisture. These damp materials are a good source for mold to grow. If the relative humidity remains high (above 60 percent) for an extended period of time, mold almost certainly will grow.

Seasonal Changes

Heated air can trigger moisture problems because it holds more moisture than cool air. Consider what happens in the fall or winter. The warm indoor air comes in contact with a cold surface (single-pane windows or non-insulated walls). The air then cools down and excess moisture condenses. That moisture can lead to mold and mildew.

Damp Concrete

A commonly asked question is..

Can mold grow on concrete?

Wet or damp concrete slabs often contribute to indoor mold problems. Concrete absorbs water like a sponge. That, in itself, is not a problem. However, anything attached to wet concrete, such as wood flooring, carpet, cabinets, wood framing, and so on, can all absorb the moisture from a concrete slab. These materials then become ideal food sources for mold.

Concrete can get wet in any one of several ways. The lack of a good moisture barrier under poured concrete slabs can be a problem because moisture can wick up into the concrete from the ground that’s damp or wet because of improper irrigation or drainage.

This is sometimes a problem in California where the land slopes toward structures, enabling rain and irrigation water to flow to the slab, where it becomes saturated.

In some cases, the concrete may never have finished drying after being poured. Contractors who are under pressure to meet completion deadlines may not allow the concrete sufficient drying time before beginning construction. That means the slab stays wet for months, even years longer than it should, never really drying out.

Whenever there’s a water or moisture problem, it’s not long before there’s also a mold problem. That’s because mold grows quickly under wet or damp conditions.

“Molds can cover large areas within 24 to 72 hours after water damage occurs,” says Dr. Luke Curtis, a medical doctor, and Certified Industrial Hygienist. Dr. Curtis has assessed more than 1,000 buildings for mold and moisture problems as well as other issues of indoor air quality.

Molds: the Good, the Bad, and the Ugly

Believe it or not, many molds have beneficial effects. They aid in the decay of dead things, are the source of such antibiotics as penicillin, and are used to make cheeses. Some are also used in the commercial production of enzymes and hormones.

However, many molds also have harmful effects. They can grow on bread, foods, and dairy products. They can damage grain, fruit, and vegetables, and livestock feed, resulting in financial losses for farmers. They can also cause diseases in garden plants. Some even cause athlete’s foot or ringworm.

Mold spores, whether dead or alive, can also cause a number of adverse health problems in humans, especially those who are sensitive to molds. Symptoms include nasal stuffiness, eye irritation, wheezing, or skin irritation.

Thrasher says the prevalence of mold in America is so great that he calls it a hidden pandemic. He estimates as many as 40-percent of all American schools and at least 25-percent or more of all homes are believed to be affected by mold and microbial growth due to water intrusion.

He believes part of the problem is caused by shoddy construction.

He explains, “One thing that I have seen and observed by working with individuals in the field who understand construction, is that construction is extremely poor in the homes we have today. Plus, they’re using materials that are tremendous good food material for the microbes.”

He notes that homes with a basement often have no water barrier between the earth and the concrete wall of the basement. The same thing with the foundation – there is no water barrier. As a result, water from heavy rains and watering the lawn goes right into the foundation and the basement…and then the moisture wicks up through the home, increasing humidity.

“All of that increasing humidity, anything above 60 percent, is going to lead to the growth of mold and bacteria…people have to be very careful about this situation. That’s the reason why I call it a pandemic.”

Assessing a Mold Problem

If there is only minor surface mold, usually the home or building owner doesn’t need to call in an expert, but if the mold is widespread, has caused visible damage, and is suspected of causing health problems, it’s best to call a professional who is certified and trained in dealing with mold.

Professional Assessing Mold
Certified professionals trained in mold assessment and mold remediation typically belong to one of two certifying organizations: NORMI (National Organization of Remediators and Mold Inspectors) or IICRC (Institute of Inspection, Cleaning, and Restoration Certification).

Another type of trained professional who also assesses and remediates mold is the Certified Industrial Hygienist. A CIH member typically belongs to the American Board of Industrial Hygiene (ABIH) or the American Industrial Hygiene Association (AIHA).

It’s important that people with mold problems hire someone who is trained in mold identification and remediation. Mold assessment and identification presents many challenges and can easily be done improperly by untrained persons. For instance, in the aftermath of Hurricanes Sandy, Irene, Rita, and Katrina, many companies sprang up claiming to understand the issues of mold contamination.

Yet they failed to follow proper protocol and, as a result, many homeowners and business owners lost both their properties and money to these unscrupulous firms.

Ron Guncheon, owner of RMS Environmental in North Palm Beach, Fla. and a certified member of NORMI, explains that mold specialists can approach a mold situation in one of two ways. By state law, they can either do a mold assessment or mold remediation. They cannot do both since to do so would be a conflict of interest.

A mold assessment determines if mold is present. This is done by visually examining the premises and testing.

When Guncheon does an assessment, he begins by sitting down with his clients to find out if they have any health issues, such as a running nose, trouble breathing, nasal stuffiness, or any other respiratory symptoms.

He also asks if their symptoms occur outside the home or only at home and if there is one particular room where the symptoms appear.

“I’m looking for signs of reactions people will have when they get exposed to mold and mold spores. After that, I conduct a visual inspection indoors and outdoors.”

He looks for visible and odor-causing signs of mold. This may involve checking many different things such as baseboards, beneath carpets, air conditioners, ventilation duct work, beneath sink cabinets, showers, and even outside walls. If he can’t smell or see any signs of mold, he uses an infrared camera to look for hidden moisture.

Free Download – Is a Pin or Pinless Moisture Meter Best For You?

How to Find Moisture Behind Walls

Moisture present behind walls or beneath floors can be detected with a sensitive infrared camera which produces a vivid temperature map of wet areas. The temperature difference created by the presence of moisture on the inside surface of a wall will appear differently than the surrounding area. In other words, materials that retain moisture are cooler than things that are dry.

Although infrared inspection is a fast, non-invasive method to discover moisture intrusion within a home or building, it does not directly detect the presence of mold. Instead, it’s used to find and point out moisture spots where mold may develop.

“Once I find an area where there is moisture or water vapor, I use a moisture meter to tell me the level of moisture present. If the level is too high, there’s a good chance mold is growing as a result. I then take a picture of the meter’s reading to document my findings,” he says.

Click here to purchase an Orion 950 moisture meter

Wagner Meters offers mold specialists the Orion® 950 smart pinless meter to make documenting moisture levels easy. The Orion 950 uses electromagnetic technology to provide a non-invasive tool for measuring moisture in a wide range of materials, including wood, synthetic stucco, plaster, drywall, insulation materials, ceramic tile, shingles, linoleum, concrete, and more.

The Orion 950 provides a general comparison moisture indication for inspection applications that might require relative moisture content (MC) readings. By establishing a known baseline dry MC reading on a building material, it can then compare and pinpoint elevated MC problem areas or conditions.

Other Necessary Tests

Guncheon also tests the indoor temperature and relative humidity throughout the premises, checking for unusual differences between rooms. He says the optimum indoor relative humidity should be between 40 and 60 percent. Anything higher can lead to mold.

When there are hard-to-reach areas to examine, such as cavities in ceilings, walls, and floors, Certified Industrial Hygienist Dr. Curtis sometimes employs fiber optic devices to detect moisture. Some fiber optic devices carry light into confined spaces while others have a video capability that allows the user to see close up what he cannot easily access.

“A number of investigators even use dogs trained to sniff mold. I, myself, once used a mold-sniffing dog to find heavy mold growth in a hard-to-reach ventilation duct,” he says.

Whether or not mold is found, Guncheon takes samples which he then sends to a qualified lab where they culture and identify any mold species that might be present. He uses three to five methods of sampling depending on what the client wants to pay for. They include:

  • Air sampling – a device sucks in the air for 5 minutes to collect whatever is floating in the air. Samples are sent to a lab.
  • Petri dish – portions of the mold are dropped onto a Petri dish, which is then sent to a lab.
  • Tape lift – mold is collected on a sticky tape and placed in a special ziplock bag that’s sent to a lab.
  • Bulk – parts of the contaminated area are removed and sent to a lab.
  • Swab test – a Q-Tip®-like swab is rubbed against a surface. It’s put in a test tube and sent to a lab for mold identification.

If he cannot find any moisture or water intrusion, cannot locate mold growth or the client has had mold testing done previously with no evidence of mold yet they’re still having problems, he conducts a VOC (volatile organic compounds) test. Since molds and many other things in a home or building give off VOCs, this device will accurately monitor what they are.

The VOC machine runs for 2 hours in an area to collect VOC samples, which are then sent to a lab for identification. If there is evidence of mold or other compounds, the lab will tell him what they are and if those levels are acceptable, moderate, or excessive.

He presents his findings in a report which he gives to the client. Those findings typically include identifying the problem and its cause, locating the mold, determining its cause (e.g., broken pipe), identifying the mold species, and describing what needs to be done to correct the situation. Corrective action may be simply sanitizing and fogging the premise with a biocide to kill the mold and its spores, or it may require moderate to extensive mold remediation.

Mold Remediation

Mold remediation is simply a professional term for mold removal. If remediation is necessary, the assessment details what is required to remove it.

It’s up to the client to follow through on the assessment. He can plan to do some of the work himself (e.g., tear out a wall) or hire a mold remediation specialist to handle everything carefully and keep the contamination to a minimum.

The client also has to decide who does the build back. For instance, if a wall is opened up, the client has to decide whether the remediation specialist repairs the wall, or someone else does the work.

Guncheon says that if he finds an infested wall, say in the bedroom, he might recommend that the whole area is to be walled off from the rest of the house. In other words, he builds a containment wall of 6-mil plastic with a zipper entrance. The containment wall is held in place with tape and supports and attached to the walls, floor, and ceiling so that the area will not contaminate the rest of the house.

“I use negative air pressure to exhaust to the outside whatever mold spores and contaminants are present in the room. (This is similar to turning on a bathroom vent fan to remove steam.) If you have water in the room, it has to be dried out first before proceeding.

“Inside this area, I use HEPA (High-Efficiency Particulate Arresting) filtered air purifiers or air scrubbers to trap and collect microbials in the air that are down to 3 microns in size. These scrubbers are like big filters and the collected material is exhausted to the outdoors. So what we’re doing is forming a negative air pressure so that the air from the main part of the house is being drawn into that area and then exhausted outside. If we don’t do that, then we’re allowing the spores to roam freely through the rest of the house,” he adds.

Wearing protective gear, such as HEPA-filtered respirators, goggles, latex gloves, and protective personal equipment suits, Guncheon begins taking the affected area apart. Removed parts, such as drywall or damaged wood, are carefully placed in a bag.

Once the affected pieces are bagged, every inch of the area is carefully HEPA vacuumed again to trap any spores.

The area where the mold is growing is also carefully removed using special equipment and the area is thoroughly sanitized with a biocide. In some cases, he may fog the entire house with an antimicrobial agent.

Experts advise against using ammonia or bleach to “kill off the mold.” In fact, neither one is an EPA-approved biocide.

“What happens is you’ll kill the mold but you’ll leave the carcass behind. The carcass will disintegrate and can cause toxins to be released into the air. So you really went from one problem (mold growth) to another problem.

“Another thing to keep in mind is that bleach only kills the mold spores are on the surface of wood or other organic material. The mold, however, tends to grow and establish roots below the surface and into the organic material. Due to the chemical makeup of bleach, it does not absorb into wood or other materials. Then, once moisture is reintroduced in the environment, the mold will grow right back,” Guncheon explains.

Build Back

Once the mold is eliminated, the source of its growth (e.g., broken water pipe) corrected, and the affected areas removed (e.g., portions of a wall damaged by mold), the final step is the build back. Here the client can decide to have the mold remediation specialist do the repairs, hire someone else, or even do the repairs himself.

In Closing

Mold is everywhere. There’s no escaping it, but we can keep it from becoming a problem by eliminating moisture and excess humidity from indoor environments.

When mold does appear, it can not only damage property but cause adverse health effects as well. That’s when it’s best to hire a trained and certified mold specialist. He has the knowledge and the proper tools to find, identify and eliminate the problem.

Written by Wagner Meters, published first as a 3 part series by ICS Cleaning Specials (Aug/Sept/Oct 2014)

Last updated on July 26th, 2023


  1. Marliese Hogan says:

    I started noticing a moldy odor under my bathroom cabinet that has only gotten worse. I called a plumber and he replaced a vent cap under the sink but the odor has not improved. I checked the outside wall and noticed a general wetness from a rain downspout and ac unit right where the inside cabinet would be. I also noticed a hairline crack in the tiling coming from under the cabinet and extending a few feet into the bathroom. I am thinking that it may signal that the concrete slab has been affected. Who can I hire to resolve the problem? We may need to remove the bathroom cabinet and the tile to see if the concrete is compromised. I am panicking! What do you advise? Thank you.

  2. Kurt Garza says:

    Mold spores can cause many types of health risks, especially to those susceptible to allergies and respiratory problems (such as asthma), and they can cause inflammatory rashes, headaches, and other flu-like symptoms. So whenever you’re around the concrete mold, make sure to take the proper precautions.

    Kurt |

  3. Zoe Campos says:

    Thank you for warning me that molds might cause visible damages to our house and possible health problems. My neighbor mentioned that she had seen a few mold spots in her home and I’m afraid that my children might be exposed to them too if I’m not being careful. It might be better to hire experts in mold prevention and let them check our house for any signs.

  4. Ron Booker says:

    My wife is worried that we might have a mold issue in our downstairs basement. I appreciate how you mentioned that concrete absorbs water and it could lead to the growth of mold. We want to stay healthy so we’re hoping to find a reputable professional who can come and inspect the house for us.

  5. Sabrina Addams says:

    My best friend and her husband live in a very rainy, cold climate and said that there’s going to be a lot of storms this season there. It’s good to know that if they need to get rid of mold, mold remediation services can help them to decrease contamination or tear out walls if they need to. I’ll let them know that they should look for a professional if they do see signs of mold in their home.

  6. Greta James says:

    Wow, I had no idea about your point that concrete can absorb water like a sponge and grow mold. About a week ago, my sister got everything moved into her new home. However, as I was helping her move I noticed there is a spot on the floor that never really dries because of a leaking sink. I wonder if she should look for services to look for and remove mold.

  7. Eileen Benson says:

    It made sense when you said that training is important in mold assessment and remediation due to the challenges it presents. My husband and I have started to notice a musty smell in our home’s guest bathroom and think it might be due to mold. Your article helped convince me that hiring a professional mold testing service would be worth the cost!

  8. susan houck says:

    i purchased a house totaly built of cement in 2000. i soon discovered, cracks in the celing,in the kitchen, water actually dripped on my head as i did the dishes, visual cracks were now present. also in the living room from the front door to the den which was the living room to den , there was a crack and water dripped from around my lite fixture there in the living room and in the den i had to put a bucket to caught the drips of water. the roof was cement as i mentioned and the person i was buying the house from incisted i slap a screw in the den roof inside the house and use repair cement on the other problem areas. he didnt want me to fix it by removing the dirt from the roof, exposing cement as he didnt want the insurance claim to follow the house, like it would cause the house to be devalued. so molld, sicknesses and mold smell were what i lived with. . i moved out in 2011 and the house was given back to the owners i was purchasing it from. it has since been bandaged to sell ,paint , roof was built over the dirt roof, never fixed.. and now its up for sale for 279,000 thousand dollars. how can i get the national organization of remediations and mold to help me have these owners exposed for negulence of proper repair to this house. the ceiling concrete was almost 3 feet thick with rebar, as wellas the rest of the house, and it leaked water on my head. any direction to expose this man and keep someone else from broncitis,cronic, phemomia, flu like symptom, arthritis.. i loved the home, it isnt what they portray it to be even more now, help. and the mold smell in carpet, furniture i smelled like mold out in public, my son couldnt even spent one nite in it, his throat would swell, eyes he couldn even be there and now their selling to a family, first time home buyers, and have not done the proper repairs? i would really appriciate some advice on how to mke the owners do all the testng i read about in this wagner meters article, thanks

    • Ron Smith says:

      Hi Susan,

      Thanks for the comment. I think it would be best if you contacted regarding your situation. Best of luck.

  9. Doug Dickison says:

    We live in CA in a home on a downward pitch. My wife noticed a musty smell not long ago. Perfect timing as I was preparing to paint the closet, I pulled up the old carpeting (that was to be replaced), & I noticed a white crystaline(?)powder in between the old floor tiles. Can I pull up the old tiles, put some type of sealant down, and then proceed with the carpet replacement?
    Thank you for your reply

    Doug D.

    • Ron Smith says:


      First, I would determine what the crystalline powder actually is: a salt compound, some type of mold, etc. Is the subfloor wood-based or is the carpet on a concrete slab?

      Feel free to give us a call, and we might be able to steer you in some direction.

  10. Ileana Ortiz says:

    Living in a townhouse. My bedroom is on the bottom floor , along with the shower and laundry area. My bedroom area is carpeted . The carpet stays so moist that when I walk, it shows footprints. I’m thinking that a dehumidifier might work to remove the humidity. Should i remove the carpet and check for mold?

  11. AJ says:

    I built my home 3 years ago and there is a mold problem. It is coming up through my slab. I noticed it a year or two in my garage. I live in south Louisiana so I didn’t pay much attention to it at first. Now almost the entire floor in my garage has some sort of mold spot on it. I keep a pump full of bleach and periodically spray it but it comes back. It is now in my home. My AC vents have mold around them. So much so that when I clean it off the paint is coming off with it. On the floor all along the front wall of my house is almost a constant condensation. The AC panel reads that my house is alway above 50% humidity, usually 65-80%. How do I correct this problem?

    • Ron Smith says:

      Mold needs warmth and moisture to grow. You definitely have both. It may have initially started from the moisture coming up from the ground underneath your slab (I assume that the slab was not poured on a vapor barrier material).

      Regardless, the sources of the excess moisture must be identified and eliminated for you to have a chance of stopping this. But, you now have mold existing throughout, and this may require some serious remediation. Two national organizations that are involved with this are National Association of Mold Remediators and Inspectors (NAMRI), and the National Organization of Remediators and Mold Inspectors, (NORMI),

  12. Blanche Duncan says:

    Good Morning
    There was a leak where tile in shower inside wall. For over 2 years. The tile was soft and cave in. It’s was black thick stuff growing on faucet all between copper pipe and green and black fungus all over. I have health issue
    I took pictures of faucet and other material. They send plumber fix leak. He was concerned. But it’s not his job. Please help me.

  13. Matt says:


    Have recently found a shower drain leak that had been leaking water under the foundation of my house. My question is, since I know we have mold spores in the air, based on my environmental test, and I know the active water source is now fixed, will the mold just die off after they reinstall my shower? Can mold spores travel through concrete? If there was active mold growth in the dirt under my foundation, how would that ever be able to be fully dried out and remediated? With health concerns in mind, what would it take generally to say that the mold is completely gone and is no longer a health concern. Keep in mind the mold spores in the room closest to the leak were close to 800PPM and around 200 on the opposite side of the house where there was no active leak. Any advice would be greatly appreciated.

  14. Michael Smith says:

    I just purchased a home and pulled all the tile. laminate, and carpet up today. The laminate flooring had a water barrrier in one of the rooms I pulled that up and alot of the rooms concrete floor is black also alot of little cracks everywhere..There is a couple other black dusty spots in the master bedroom concrete floors.These two rooms are seperated by the master bathroom..Can you help me with some advice please?

  15. Randy chapman says:

    My home is built on concrete slab, it appears I have mold or mildew only behind my 7 foot kitchen cabinets. No where else in house. Have no idea what caused this. Can you help me out here?

  16. Ri says:

    Thank you. The basement concrete was there when they moved into the house in 1973, the house was built in 1962, unsure about vapor barrier. The basement floor is a cement slab with a sump pump installed 10 years ago, no flooding just precautionary, within that same corner gray discoloration and paint puckering occurs. My parents had two metal cabinets that have both rusted out in that area. Could the blotchy areas be mold? How would you recommend trying to resolve this? Do you know who could help with this issue in MD?

    Thanks again. I did not notice you responded, would of responded sooner.

  17. kinobe medi says:

    I have a flat double house but there is moisture under ground how best can I deal with this issue

  18. Ri says:

    My parents appeared to have a moisture problem in their below ground basement for many years. My dad had tried to waterproof it many years ago. It appeared to help and occasionally my mom would spray bleach on the wall, when it looked like blotchy discoloration very noticeable on a white cement wall. Approximately 6 years ago they had a large diseased tree removed from their back yard and since then it appears that the blotchy basement areas have increased on the walls that are closest to where the tree once resided in the yard. Could there be any correlation to increased moisture and tree removal, even the area where the tree was keeps sinking even after adding dirt and rocks. Any suggestions on cause and treatment?

    • Ron Smith says:

      Sounds like water ingress to me, but cannot be sure that the tree removal has anything to do with making it worse, other than perhaps the tree roots were taking up some of the water.

      Was the basement concrete floor poured on a vapor barrier, and were the walls protected with the same? Probably not, just guessing the age of the slab.

  19. I have a mobile home it sweats which is getting the new insulation and sheetrock wet how can I stop this from happening the metal walls sweat so bad it’s getting the new insulation and drywall wet which is cousin mold I put up new insulation and drywall and is all wet do 2 the wall sweating how can fix this problem

    • Ron Smith says:

      Too high of a relative humidity inside can be one of the causes. The metal walls getting wet seems to be due to big outside-to-inside temperature differential. I am thinking it is very cold outside right now. Does this make sense? Is the inside face of the metal wall getting wet?

  20. I have mold in me condensation in my walls on my mobile home and it’s creating mold and getting the new insulation and sheetrock wet how can I fix this

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