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Indoor Mold and How It Grows and Spreads

The Science of Mold & How it Grows


What is Mold?

Fungi are a diverse group of single-celled organisms that include mushrooms, molds, mildews, smuts, rusts and yeasts. Mold and mold spores are found both indoors and outdoors in the air and on surfaces. They are decomposers of organic matter such as wood, plants, fabric and animals. Where there is decaying organic matter you will find greater concentrations of mold spores.

Once mold finds organic matter for nutrition it can begin growing on a variety of surfaces


How Does Mold Live & Grow?

When the environment is favorable and the right amount of nutrients (organic material for it to feed on), moisture and oxygen are present with an ideal temperature, mold can begin to grow. The moisture that molds thrive on can be obtained directly from standing water or from water in the air (humidity).

Moisture in buildings is usually caused by high humidity, plumbing problems, flooding or leaks. Several other factors, including building design, the local climate, ground moisture, lifestyle of the occupants and the number of occupants, can affect it as well.

The most common sources of excess indoor moisture within a building are:

  • Roof or window leaks
  • Plumbing leaks within walls and floors
  • Plumbing leaks under or behind sinks, counters, appliances
  • Backed-up plumbing / overflows
  • Flooding from rain or exterior drainage issues
  • High humidity from improper ventilation, high number of indoor plants, high number of building occupants, or elevated outdoor humidity


What Does Mold Look Like?

Mold colony growths can have a variety of different appearances depending on the species, stage of growth and growth media. Often mold has a fuzzy, wooly or spotty appearance that can be black, white, brown, gray, yellow, orange, red or green in color.

Mold can have a wide range of colors, shapes and depths


How Does Mold Enter a Building?

Outdoor mold spores commonly can enter a building through the air or by becoming attached to people, animals, or other materials that are moved into a building. Mold spores are very small and cannot be seen with the naked eye. A spore is a mold colony’s “seed” and is released natural into the environment to colonize. Spores are resilient and are built to with stand extreme environments so the spread of colonization reaches a larger area. Once the mold spores settle on to a viable substrate they will grow into a mold colony. A visible mold colony can house millions of spores. An area the size of a postage stamp can contain up to 65,000,000 (65 million) spores. This is more than enough to potentially spread across the interior of a property and cause mold growth where conditions are ideal.


How Does Mold Grow on Building Material?

Certain products, even if considered artificial or synthetic, can contain trace organic nutrients that molds can thrive on. These can range from common building materials, such as paint and drywall, to the clothing in our closets.

A few common building materials and other items that mold can grow on:

  • Drywall/Sheetrock
  • Paint
  • Wallpaper
  • Wood
  • Hard Wood Flooring
  • Baseboards
  • Insulation
  • Carpet
  • Carpet Pad or Tack Strip
  • Fabric or Leather
  • Food
  • Other Items Containing Organic Matter

Mold can grow on a variety of surfaces and range in appearance from a black or green patch to a full grown mushroom

Mold can grow anywhere in a property where it can find moisture and a food source. The most common locations where mold grows is within wall cavities, usually in bathrooms, kitchens or other moisture-rich environments. Mold is also commonly found in attics, crawlspaces and basements. Mold in attics usually results from a leak from the roof, an attic plumbing failure or a leaking air conditioning unit. Mold in the crawlspace or basement often relates to improper drainage that leaves standing moisture under a property.

While these are the most common locations for mold to grow, mold can grow virtually anywhere in a property where it can find moisture. Mold has been found in every type of room is every type of building from the bedrooms and family rooms of homes to private offices and even elevators in office buildings.


To learn more about mold, indoor allergens and how they can affect your health, click here.

To get more information about mold and how it can affect you and your property, call us at 866-358-3838 or submit an Online Contact Form to receive a return call or e-mail.

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