How Long Does It Take For Mold to Grow?

We may be paid a commission if you purchase through links on this page. This does not affect our opinion or editorial process. More info.

It can take only 24 to 48 hours for mold to grow after the ideal temperature and moisture levels for mildew to grow are present. It doesn’t take long (sometimes within 3 days) for mold to then become visible.

However, you can prevent this type of propagation by carefully tending to some of the most at-risk areas of your house.

Flooding, a leaky roof, and a burst pipe – all of these in-home emergencies are a cause for immediate concern. While abating any influx of uncontrolled water in your home is problematic enough, your troubles may not end after the water is cleared away. Indeed, if water soaks into your ceilings, floors, and walls, you may be at a greater risk for mold growth than ever baefore.

In many cases, even a damp environment caused by ambient water vapor can promote mold growth in areas without much air flow. Regardless of its causes, mold in your home is bad news in need of immediate attention.

Failing to address an emergent mold problem can put your family’s health at risk, with the CDC noting that many common indoor molds can cause fevers, shortness of breath, and severe illness for people with compromised immune systems and chronic breathing problems (such as asthma).

Simply put, you need to understand the risks related to indoor mold, starting with the amount of time it takes to grow and continuing through the areas where it grows most efficiently. From there, you’ll be prepared to address mold risk factors in your own home or contact a specialist who is trained at identifying the same. Either way, this guide will help you understand indoor molds like never before.

how long does mold take to grow

Disclosure:It is important you understand that we may receive commissions when you click our links and make purchases. However, this does not impact our reviews and comparisons. All opinions are our own we pride ourselves on keeping our articles fair and balanced. For more info see our disclosure statement.

How Long Does It Take Mold To Grow?

close up of mold growth

A Mold Growth Timeline

In the wake of a sudden in-home water leak, most folks are pretty preoccupied with the process of containing and diverting the problematic water. Once that job is done, most people feel satisfied that their work is complete, especially after proper repairs have been made. But if any walls, floors, or ceilings became saturated during the leak, there is a decent chance that mold may try to take up shop there in the coming days.

After 24 hours: Specifically, most types of common in-home molds (cladosporium, penicillium, alternaria, and aspergillus, according to the CDC) can land on a suitable surface and germinate with as few as 24 hours. At that point, there will not be any obvious signs that mold spores are present in the area. Because mold spores are fairly contained at this stage, it is often the best time to eliminate them through cleaning with diluted bleach.

After 12 days: However, if the mold spores are not detected during the germination stage, they are prone to colonize in as few as 3 days, with most types of mold gaining stable footing by 12 days post-germination. Even at this stage, mold may not be visible to the eye on the afflicted surface. However, mold spores at this stage can begin to spread more effectively if the air in the area is not properly dehumidified.

After 18 days: Once you pass the 18 day threshold, you will almost certainly see the visible signs of mold begin to crop up on the afflicted surface. While the precise appearance may vary, most mold types are recognizable due to their dark color and spotty appearance. At this point, any cleaning of the afflicted surface will need to be far more thorough and accompanied by proper airway protection.

All of these time frames are estimates, however, with specifics for mold growth speed based primarily on the surface’s temperature, the surrounding air temperature, the level of moisture in the surrounding air, and the amount of airflow in the afflicted space. Controlling each of these factors after a major water leak is often the best way to prevent mold from taking hold in your home.

How Does Mold Spread?

how to remove mold from drywall

Though it may be a small comfort to homeowners, mold of one kind or another is almost always present indoors (unless it is being removed through an air filter). As such, there is always a chance for mold to land on a given surface within your home. However, mold spores usually don’t take root because they lack the two ingredients they need to survive: food and water.

Note: You can reduce the amount that mold spreads by using an Air Purifier to filter out the spores from the air.

What Does Mold Feed On?

First, let’s consider mold’s food. In theory, most any type of organic matter can serve the needs of common indoor molds. That being said, surfaces that are porous (such as wood) tend to fall victim to mold growth due to the manner in which they break down easily. As for water, mold only needs as much water as is in humid air to subsist and thrive when temperatures are just right.

If these two factors are present, mold is able to germinate, colonize, and spread as described above. This spreading process is not unlike the ways in which trees spread their seeds, though mold spores are invisible to the naked eye. While an initial mold colony may orbit around a single point, prolonged mold exposure can cause an entire object or an entire room to become a haven for mold growth.

The Spreading Process Is Quick!

Mold can start its spreading process within hours, and while you can’t see the process happening visually (yet) getting leaks and ambient moisture under control in short order is exceptionally important. If you are unable to clean up an at-risk area immediately, make a plan to thoroughly clean that area with bleach or dispose of the moistened object if it is not worth saving.

For more insights into proper mold cleaning procedures, check out these posts:

How To Stop Mold From Growing After Water Damage

The key to stopping mold growing is getting the area dry as quickly as possible. Without moisture, mold will not grow.

1. Remove Excess Moisture

Get rid of all the visible water and moisture you can using any means possible.

Methods that work include:

  • Using a broom to push water out
  • Using buckets to remove large puddles of water
  • Soaking up water with towels

2. Dry The Area Out And Keep It Dry

Once you have removed all the visible area, you need to attack the moisture that is harder to get to.

Use the following methods to dry out the area (and keep it dry) more completely:

  • Use a dehumidifier to dry remove the moisture from the air
  • Use space heaters to heat up and dry furniture, carpets, and drywall
  • Use fans to keep the air moving and dry

Keeping the area as dry as possible is key to stopping mold from growing.

Areas Most At-Risk for Mold Growth

water damage leading to mold growth

When it comes to identifying and abating mold in your home, one of the most important steps is to isolate areas that are at the greatest risk for mold growth. Generally speaking, these areas are most often those that contain a lot of natural moisture or have been exposed to an excessive amount of moisture due to a roof leak or pipe burst. However, other types of environments are more likely to foster mold growth than those in warm, dry, well-lit areas.

Mold spores are more likely to come to rest on and colonize surfaces made from natural fibers, including cotton, wool, paper, leather, and wood.

Meanwhile, inorganic surfaces covered in organic material, such as food, grease, or soil, are likely to encourage mold growth as well.

Also, mold doesn’t need light to thrive. In fact, darker areas with less air flow tend to be ideal homes for mold spores. Even if improved conditions are temporarily introduced, spores can become dormant until ideal conditions for growth return.

Though it’s not an exhaustive list, these are some of the common in-home areas where mold tends to accumulate due to their natural conditions:

  • Basements
  • Crawlspaces (particularly those built over uncovered earth)
  • Laundry Rooms
  • Attics (consider roof vents)
  • Under Cabinets – Check out our guide on waterproofing cabinets.
  • Drywall
  • Behind baseboards
  • Tile
  • Grout and caulking


At the end of the day, in-home mold is no laughing matter. Mold can grow in a damp environment in as little as 24 hours, leading to damage on the afflicted surface and decreased breathability of the room’s air. If you have recently experienced a serious water leak in your home, you should take some time and check all of your at-risk areas to ensure this harmful contaminant is nowhere to be found.

Should you find mold, begin cleaning it up right away after you’ve obtained the proper protective gear and cleaning materials. Then, be sure to keep an eye on the area and introduce environmental control elements to decrease the likelihood of a recurrence.

If you have any more questions about mold or the best ways to clean it up, be sure to leave a comment for our community members to answer!

Do you have any questions relating to this article? Email us at e[email protected] or call us on +1 (310) 961-4908

This content may contain affiliate links. If you purchase through these links we may be compensated. More info.

Photo of author
Aaron is the founder of and Essential Home and Garden. With over 15 years of hands-on experience in home ownership, lawn care, and gardening, Aaron is a seasoned expert in areas like lawn care, DIY, HVAC, and pest control.

Leave a Comment