How Long Does it Take Mold to Grow? - Cleanfax (2022)

Q : How long does it take mold to grow?

A: Interesting question. As a technician who has performed many water damage mitigations and mold remediations, the answer to this question has always been elusive.

In my experience, when performing water damage mitigation work on some projects that had been wet for two or three days when we arrived, there was minimal indication of microbial growth.

If there were any indications, it was usually that “musty” odor, which we know are microbiological volatile organic compounds (MVOCs). We normally associate these odors with mold growth.

But, with no visible signs of mold growth, was mold contamination an issue? Or could the problem have been something other than mold?

On other jobs, upon arrival it was immediately apparent that the building had more issues than just being flooded. In these instances, we observed visible growth, assumed it was mold and determined that the site would have to be properly remediated.

From the 2002 New York City Guidelines of Assessment and Remediation of Fungi in Indoor Environments, the inference was that mold would begin to grow in 24 to 48 hours. That statement was removed in the 2008 version. Additionally, the U.S. Environmental Protection Agency (EPA) in its publication, Mold Remediation in Schools and Commercial Buildings, references the time line of 24 to 48 hours to prevent mold growth and states that “even if materials are dried within 48 hours, mold growth may have occurred.”

While both publications do not specifically state that mold begins to grow in 24 to 48 hours, this is the generally accepted time frame used by water damage responders to determine when mold begins to grow.

So we have the inference from the guidance documents that mold can begin to grow in 24 to 48 hours. We also have personal conflicting evidence: On some losses mold seems to grow, and on other losses mold does not seem to grow.

Observations from mold jobs

Being a mold remediator/educator, I have gathered similarly confusing, often conflicting input, from numerous jobs.

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We observed that mold grew on some surfaces, but not others. We learned that the type of mold contamination found in homes is almost always what is called saprophytic mold. Saprophytic mold lives by decaying dead organic material, meaning the major ingredient we build with in North America — wood and wood-related products like paper on drywall.

Additionally, research has shown that different types of saprophytic molds (different species) prefer different types of organic material (food), and different temperatures. They also prefer different amounts of wetness, usually called moisture content, but is correctly referred to as water activity.

So does mold really begin to germinate and grow (the term used in the mold world is colonize) in 24 to 48 hours?

In doing major mold remediations, the usual process is to work in conjunction with an industrial hygienist (IH) or other mold professionals, such as a certified industrial hygienist (CIH) or indoor environmental professional (IEP).

Their job is to help identify what the contamination issues are, quantify the problem/issues and prepare a working plan, or protocol, for remediation.

In some situations, the IH will take samples from a suspect surface with a sterile swab. Sometimes the IH will collect air samples directly onto petri dishes containing an agar food source favorable to most molds.

The samples are sent to a qualified mycology laboratory. The material collected on a swab is “plated” onto a petri dish like that used for air samples.

The lab will “culture” what the IH has collected under ideal conditions of temperature and humidity in an incubator.

Payam Fallah, a PhD mycologist with the Indoor Environmental Hygiene Laboratory (IDEHL), reported in a personal communication with me that, in the lab, spores begin to germinate and form microscopic structures in few hours. The first tiny visible colonies of fast-growing mold types may arise in about three days (72 hours).

Colonies become large enough to visibly identify and are counted in about four days (96 hours), before the petri dish is overgrown.

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Some slow growing types of mold may not grow colonies fast enough within this time frame. A technical report will be prepared advising “what” species of mold grew and “how many” colonies of each were observed.

But… if it takes 72 hours for mold to germinate and grow on samples that are in a lab under ideal growth conditions, then how can mold germinate and grow in a normal building in 48 hours?

Mold Growth—A real-world test

When Restoration Sciences Academy instructors were writing our mold manual for the three-day and four-day mold courses, this same question became a major unanswered point. We decided to run an experiment.

During the late summer at our Pittsburgh facility, we decided to see if we could determine how long it takes for mold to colonize (grow).

We took a normal 4-foot by 8-foot by ½-inch piece of drywall, cut it in half, making two pieces with dimensions of 4-foot by 4-foot each. One piece was placed in a wallpaper wetting trough, and the other was left alone leaning against the wall (what would be called a “control” specimen).

Both pieces were placed in a two car garage. The trough with the drywall was filled with water. Both pieces were allowed to just sit there. We filled the trough every day as was needed, and took pictures every two to three days.

The garage door on the facility was opened and closed, as the building was used for other work. As such, the garage area was exposed to normal outdoor air, including airborne mold spores.

Temperatures ranged from a low of 60 degrees Fahrenheit to a high of 85 degrees Fahrenheit. The humidity levels were not recorded, but were typical for the month of September in Pittsburgh.

This was just a “let”s see what happens” experiment, not a scientific experiment; therefore, we did not accurately monitor or try to control the environment.

Mold Growth—The surprising results

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We expected that in two to three days we would see visible mold colonies (mold growth) on the drywall piece that was in the wet wallpaper trough. What we observed was nothing.

Thinking “maybe the air is dryer in Pittsburgh” we should see mold growth in four or five days. Still nothing. At eight to nine days, still nothing had developed.

It was a full 18 days until we could see visible mold growth!

And as expected, nothing grew on the non-wet “control” piece of drywall.

Everyone who is reading this and been involved with mold is probably saying something like “It may not be visible, but it was there.”

Are you sure?

We have some very conflicting information:

  • Personal experience at water jobs: Mold does not seem to grow on every job in 24 to 48 hours
  • Personal experience on mold jobs: The labs take 48 to 72 hours to grow mold under ideal conditions
  • Non-scientific experiment where mold was not visible until day 18
  • The guidance documents imply 24 to 48 hours for mold growth.

The science of mold growth

With this conflicting information, it is time for more research.

Working in conjunction with my fellow instructors, we did a detailed scientific/technical literature review and found a peer reviewed paper entitled “Controlled Study of Mold Growth and Cleaning Procedure on Treated and Untreated Wet Gypsum Wallboard in an Indoor Environment,” by Michael Krause, CIH, with Veritox Inc.

Krause and his associates performed basically the same test that we did, except they did it with a number of untreated and treated wallboard sheets under very controlled scientific conditions.

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According to Krause, it took at least a week to confirm that invisible microscopic growth structures (hyphae) had formed on wet untreated wallboard in a closed office.

Mold growth colonies were not visible on untreated drywall until three weeks into their eight week experiment.

The first mold types seen were Acremonium, Penicillium and Cladosporium. Stachybotrys was never seen. Visible mold did not grow on wallboard that was coated with a primer.

Additionally, a study done by Dr. Michael Berry, prepared for the Carpet and Rug Institute (CRI), showed that drywall and framing lumber, when exposed to a controlled environment with a temperature of 80 degrees Fahrenheit and a relative humidity of 80 percent, did not display visible mold until week five (35 days).

Everyone who is serious about moisture and mold should read both of these studies and the references cited. Please read them before sending me an e-mail, or a letter to the editor. You will find what Krause, Berry, and other papers have proven is very interesting, and goes totally against what most of us have accepted about the amount of time it takes for mold to colonize.

In addition to Krause”s peer reviewed paper, and Dr. Berry”s study, additional peer-review research supports their conclusions that mold does not become visible in 24 to 48 hours.

A listing of a few of these papers is at the end of this article.

It is true that different saprophytic mold species colonize at different rates, and the time required for colonization is affected by different climates and different food sources. But Krause”s test, which is really quite representative of a normal indoor environment, illustrates that it was 21 days before mold growth was visible.

If a reader of this article wants a reference location for virtually everything that deals with mold — different species, affects on human health, how mold attacks different materials, affects of different chemicals, etc. — then the just released New York State Toxic Mold Task Force report is for you. It is 150 pages in length, with 108 references. In my opinion, this report is probably the most complete document compilation of what is really known about mold.

What does this mean to us as water damage mitigators and/or mold remediators? We will continue this topic soon in Cleanfax magazine.

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References:

  • Krause M, Geer W, Swenson L, Fallah P, and Robbins C. 2006. Controlled study of mold growth and cleaning procedure on treated and untreated wet gypsum wallboard in an indoor environment. J Occup Environ Hyg. 3: 435–441.
  • Berry MA, Foarde K, Mitchell C, Bolden K, Walton C, and Adams R. 2002. Final report of the hydrolab project 2001 flooring, humidity, and mold growth.
  • Menetrez MY, Foarde KK, Webber TD, et al. 2008. Testing antimicrobial paint efficacy on gypsum wallboard contaminated with Stachybotrys chartarum. Journal of Occupational and Environmental Hygiene. J Occup Environ Hyg. 5: 63–66.
  • Menetrez MY, Foarde KK, Webber TD. 2007. Testing antimicrobial cleaner efficacy on gypsum wallboard contaminated with Stachybotrys chartarum. Env Sci Pollut Res. 14(7): 523–528.
  • Price DL, and Ahearn DG. 1999. Sanitation of wallboard colonized with Stachybotrys chartarum. Curr Microbiol. 39: 21–26.

Richard Driscoll has a B.S. degree in mechanical engineering from Clarkson College of Technology, an MBA from the University of Dayton and is currently working on his doctorate. He is a professor at Webster University, where he provides graduate and under-graduate level lectures on marketing, international business management and business metrics. He is an Institute of Inspection, Cleaning and Restoration Certification (IICRC) Certified Master Restorer and an approved instructor. Driscoll has been consulted by state governments on legislation related to the cleaning and restoration industry. He also is the author and instructor for Restoration Sciences Academy”s MR-110 and MR -210 microbial remediation classes. He can be reached at [emailprotected].

FAQs

How fast does mold usually grow? ›

Mold growths, or colonies, can start to grow on a damp surface within 24 to 48 hours. They reproduce by spores - tiny, lightweight “seeds”- that travel through the air. Molds digest organic material, eventually destroying the material they grow on, and then spread to destroy adjacent organic material.

What is the fastest mold can grow? ›

How Fast Does Mold Grow? Generally, mold can grow significantly within 24 to 48 hours after water damage. Mold can take hold of your home and grow rapidly within 12 days if it has the ideal conditions it needs to thrive.

How fast can toxic mold grow? ›

Mold begins to grow as soon as its spores land on a damp, fibre-rich material (wood, fabric, drywall…) and it can spread around the house within 24 to 48 hours. It colonizes in one to twelve days and grows at one square inch per day. In less than a week, it can cover surface areas of several square feet.

How long does it take mold to grow in a petri dish? ›

Molds grow more slowly than bacteria and may appear only after five to 10 days after first use of the Petri dish.

How long before mold makes you sick? ›

These symptoms usually first appear 2 to 9 hours after exposure and last for 1 to 3 days. Other affected persons have progressive shortness of breath and cough, as well as weight loss. Work-relatedness may only become apparent over long holidays if symptoms resolve and then recur on return to work.

What removes mold? ›

A bleach solution also works to kill mold. Mix one cup of bleach in a gallon of water, apply to the surface and don't rinse. Mix a 50/50 solution of ammonia and water. Spray on the surface, wait two to three hours, then rinse.

How do you stop mold from growing? ›

To Prevent Mold Growth in Your Home
  1. Keep humidity levels in your home as low as you can—no higher than 50%–all day long. ...
  2. Be sure the air in your home flows freely. ...
  3. Fix any leaks in your home's roof, walls, or plumbing so mold does not have moisture to grow.

Does light prevent mold? ›

Sunlight and fresh air are about as “anti-mold” as it gets, plus it's easy to do. The sun is especially helpful for items that can't go through the wash. The fresh air and sunlight will keep the mold from growing on your precious items like your furniture, walls, and mattresses.

What temperature stops mold growth? ›

Set your thermostat to regulate the temperature and keep it around the low 70s. This will help prevent mold from growing, so you can enjoy your time away without worry.

How can you tell if mold is toxic? ›

Pay attention to the color and consistency: We already talked about black mold above, though it's more accurate to say that Stachybotrys chartarum has a greenish-black hue. Toxic mold can also have a grayish, soot-like texture, or a slimy, wet surface. In some cases, you may even notice furry orange or brown spots.

What kills black mold instantly? ›

Treat the Area. For a natural solution for getting rid of black mold, combine one part baking soda with five parts distilled white vinegar and five parts water in a spray bottle. Alternatively, you can use a chemical-based mold and mildew remover, all-purpose cleaners, bleach or dish soap.

What are signs of mold exposure? ›

Some people are sensitive to molds. For these people, exposure to molds can lead to symptoms such as stuffy nose, wheezing, and red or itchy eyes, or skin. Some people, such as those with allergies to molds or with asthma, may have more intense reactions.

How accurate are at home mold tests? ›

The results lack enough credibility that lawyers, doctors, insurance companies, and remediation companies do not accept the results. Consumer Reports, in fact, rated four different brands of DIY mold tests “Not Recommended,” citing the following: “In some samples, the vials with media leaked over entire kit.

Will mold always grow in a petri dish? ›

Petri dishes (also called settling plates) are designed to grow mold spores and since there are mold spores in the air everywhere all the time, you should expect to get mold spores growing on the plates.

How accurate are air mold tests? ›

Air sampling is the most accurate method for determining exposure. While a tape lift may accurately determine if mold growth is present on a particular surface, it will not tell you whether that mold growth has actually affected the indoor air quality. Only an air sample can accomplish this.

Do air purifiers help with mold? ›

Do air purifiers help with mold? Air purifiers help capture mold spores from the air, preventing them from reproducing and spreading throughout your home. While air purifiers won't help treat active mold that's already present on surfaces, they are a great way to control the spread of airborne mold particles.

What happens if you breathe in mold? ›

If you have a mold allergy, your immune system overreacts when you breathe in mold spores. A mold allergy can cause coughing, itchy eyes and other symptoms that make you miserable. In some people, a mold allergy is linked to asthma and exposure causes restricted breathing and other airway symptoms.

Can I test myself for mold exposure? ›

You don't have to sit back and accept the harmful effects of mold exposure. Getting a mycotoxin test may help you determine whether you have mold toxicity in your body. This is a great way to test whether the harmful antigens in the mold are negatively impacting your health.

Is there a spray that kills mold? ›

Moldex Mold Killer is an EPA registered 3-in-1 cleaner designed to kill, clean and inhibit the growth of mold and mildew. It destroys and neutralizes mold, mildew and their odors at their source. Bleach-free, phosphate free, non-abrasive disinfectant mold killer is safe to use on most washable surfaces.

Can I leave vinegar on mold overnight? ›

Spray vinegar onto the moldy surface and leave it for an hour. Then wipe the area clean with water and allow the surface to dry. Any smell should clear within a few hours. While it's safe to use on most surfaces, vinegar is unlikely to be effective at cleaning mold off of soft surfaces.

Will dehumidifier stop mold? ›

If the humidity in a room increases, mold will start growing in patches on walls, clothes, and more. So, to answer your question, dehumidifiers do NOT kill mold, but they do prevent it by reducing humidity. If you have a mold problem in your home, don't wait. Mold spreads as long as it has a water source.

Does cold house cause mold? ›

Mold growth can occur in cold rooms when ambient humidity is high, where there is poor ventilation, insulation failure, or when wood, cardboard, and other porous materials that can grow mold are stored in the room. Healthy individuals usually do not experience adverse health effects from moderate mold exposures.

Does mold ever go away? ›

Mold does not dry out and die but remains inactive for a while if moisture is not available. This means that it can still grow back and multiply when it is exposed to any sources of moisture. Professional mold remediation and moisture control help to keep mold at bay.

Does mold grow better in cold or warm? ›

An ideal temperature for mold growth is between seventy-seven to eighty-six degrees Fahrenheit, especially when there is a lot of humidity in the air. Temperatures have to rise above one hundred degrees or below freezing to effectively kill mold spores.

What is difference between mold and mildew? ›

Mildew refers to certain kinds of mold or fungus. The term mildew is often used generically to refer to mold growth, usually with a flat growth habit. Molds include all species of microscopic fungi that grow in the form of multicellular filaments, called hyphae.

Does leaving windows open cause mold? ›

As you might've guessed, opening windows can help reduce mold. Doing so lets excess moisture flow outside instead of settling on your walls, floors, and ceiling. Without the proper amount of moisture indoors, mold won't be able to grow.

Is mold worse in summer or winter? ›

Mold grows faster in the summer months. However, winter doesn't always mean we are in the clear. Mold loves the dark spaces in our homes. Although it does not grow at temperatures below freezing, mold can survive in dormancy and await the coming spring.

Can you sleep in a room with Mould? ›

Common symptoms of sleeping in a mouldy room include:

Poor sleep quality. Skin rashes. Struggling to breathe during sleep. In rare cases, hallucinations.

What does toxic mold smell like? ›

It's often described as musty and earthy, and may even smell like rotting vegetables or plants.

How do you test for mold spores in the air? ›

When testing the air for mold, the best option is typically an air pump that collects samples for evaluation in a laboratory. However, some mold test kits use collection film or petri dishes exposed to the air as a means of testing for mold.

What happens if you live with black mold? ›

The most common black mold symptoms and health effects are associated with a respiratory response. Chronic coughing and sneezing, irritation to the eyes, mucus membranes of the nose and throat, rashes, chronic fatigue and persistent headaches can all be symptomatic of black mold exposure or black mold poisoning.

Can cleaning black mold make you sick? ›

The short answer for most healthy people is no, black mold won't kill you and is unlikely to make you sick.

Is all black mold toxic? ›

There are many types of black mold. Stachybotrys chartarum is usually the one referred to as " toxic mold." All molds can cause symptoms in people who are sensitive to or allergic to mold. But there is no reason to believe that black mold is any more dangerous than other types or colors of mold.

Is vinegar or bleach better for killing mold? ›

Vinegar truly is better than bleach at killing mold. The EPA does not recommend using bleach to kill or remove mold, except in special circumstances. In most cases, “a background level of mold spores will remain” after the application of bleach.

What illnesses can mold cause? ›

Allergic reactions to mold are common. They can be immediate or delayed. Molds can also cause asthma attacks in people with asthma who are allergic to mold. In addition, mold exposure can irritate the eyes, skin, nose, throat, and lungs of both mold-allergic and non-allergic people.

What does a house with mold smell like? ›

Most people describe the smell of mold as musty, stale, and earthy — somewhat similar the odor of wet socks or decaying wood. Although mold smells can vary, here are some of the most common characteristics: Musty and Stale — like old socks or a stuffy attic that hasn't been aired out in months.

How do you know if your house is toxic? ›

Is Your House Making You Sick?
  1. Respiratory Symptoms – congestion, aggravated asthma or allergies, sinus infections.
  2. Cognitive Issues – foggy thinking, sleep disturbance, frequent headaches.
  3. Emotional Changes – feeling agitated or depressed.
  4. Physical Symptoms – stomach discomfort, muscle aches, fatigue, rashes, sore throat.
30 Mar 2017

What are signs of mold exposure? ›

Some people are sensitive to molds. For these people, exposure to molds can lead to symptoms such as stuffy nose, wheezing, and red or itchy eyes, or skin. Some people, such as those with allergies to molds or with asthma, may have more intense reactions.

How do you stop mold from growing? ›

To Prevent Mold Growth in Your Home
  1. Keep humidity levels in your home as low as you can—no higher than 50%–all day long. ...
  2. Be sure the air in your home flows freely. ...
  3. Fix any leaks in your home's roof, walls, or plumbing so mold does not have moisture to grow.

What does harmless black mold look like? ›

When searching for black mold, look for circular-shaped spots that are black, dark green or dark brown. Some black mold can also take on shades of orange or have flecks of white within it. Most of the time, black mold has a slightly furry appearance.

What's the difference between mildew and mold? ›

Mildew refers to certain kinds of mold or fungus. The term mildew is often used generically to refer to mold growth, usually with a flat growth habit. Molds include all species of microscopic fungi that grow in the form of multicellular filaments, called hyphae.

What kills black mold instantly? ›

Treat the Area. For a natural solution for getting rid of black mold, combine one part baking soda with five parts distilled white vinegar and five parts water in a spray bottle. Alternatively, you can use a chemical-based mold and mildew remover, all-purpose cleaners, bleach or dish soap.

Do air purifiers help with mold? ›

Do air purifiers help with mold? Air purifiers help capture mold spores from the air, preventing them from reproducing and spreading throughout your home. While air purifiers won't help treat active mold that's already present on surfaces, they are a great way to control the spread of airborne mold particles.

Can I test myself for mold exposure? ›

You don't have to sit back and accept the harmful effects of mold exposure. Getting a mycotoxin test may help you determine whether you have mold toxicity in your body. This is a great way to test whether the harmful antigens in the mold are negatively impacting your health.

Will dehumidifier stop mold? ›

If the humidity in a room increases, mold will start growing in patches on walls, clothes, and more. So, to answer your question, dehumidifiers do NOT kill mold, but they do prevent it by reducing humidity. If you have a mold problem in your home, don't wait. Mold spreads as long as it has a water source.

Does cold house cause mold? ›

Mold growth can occur in cold rooms when ambient humidity is high, where there is poor ventilation, insulation failure, or when wood, cardboard, and other porous materials that can grow mold are stored in the room. Healthy individuals usually do not experience adverse health effects from moderate mold exposures.

What looks like mold but isn't mold? ›

Mold tends to have a higher profile and can even become fuzzy, while mildew is usually flat. Mold exhibits darker colors such as deep green and black; mildew may begin as white, then turn brown or gray.

How can you tell the difference between black mold and regular mold? ›

STEP 2: Try to find the source of a musty smell.

Black mold may not have a strong smell if it's just starting to grow. Once it's matured, black mold will have a robust earth-like smell, similar to dirt or rotting leaves. Established black mold has a more pungent smell than other types of household molds.

Do you have to throw everything away with mold? ›

As mentioned above, you don't necessarily need to throw out every clothing item affected by mold. However, you need to clean the moldy clothing as quickly and effectively as possible. The longer mold stays on your clothes, the harder it is to remove.

What is worse mold or mildew? ›

Without a doubt, mold is worse than mildew. According to American Home Shield, “the difference between mold and mildew is that unlike mildew, certain types of toxic molds can result in serious health problems for you and your family.” Black mold, in particular, is dangerous for humans.

Will vinegar get rid of mildew? ›

White vinegar is a safe, natural and very effective mold and mildew killer. A study by a microbiologist at Good Housekeeping found that vinegar is 90 percent effective against mold, and 99.9 percent effective against bacteria.

What happens if you paint over mildew? ›

Never paint over mildew—it will grow through new paint, which will make subsequent cleaning and maintenance even more difficult. Wash the affected surface with a mixture of household bleach and water—three parts water to one part bleach—or with a household cleanser designed to kill mildew.

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