How does Mold Grow?

Understanding What Causes Mold

Molds reproduce by means of tiny spores; the spores are invisible to the naked eye and are able to float through outdoor and indoor air. Mold may begin growing indoors when spores land on moist surfaces and find food. “Food” means virtually any organic substance, such as wood, paper, carpet, human food, and insulation. 

It's important to understand that when someone says they have a mold problem what they actually have is a moisture problem. In today's modern homes moisture can accumulate for a variety of reasons and hence the proliferation of mold problems we are hearing so much about.


Identifying the most common sources of excess moisture which causes mold:

  1. Unforeseen accidents, such as a water pipe bursting. This needs to be addressed within 48 hours, otherwise a mold problem can really get out of hand and cause extensive damage. 
  2. Maintenance problems, such as slow leaks, constant drips, a window that hasn't been sealed properly, a shower or bath that hasn't been caulked adequately, or leaky roofs. These hidden defects are usually not obvious until you have a larger problem, as in Jane's home.
  3. Condensation. Many activities of modern day living produce huge amounts of moisture. It's not uncommon to have all family members take showers or baths on a daily basis. Then there's cooking and laundry. Bathrooms and kitchens need vents with fans that will extract excess moisture to the outside of the house. If all the water vapor released into the air of a home could escape somewhere, condensation would not occur. When homes were draughtier and open fires were common, this water mainly went up chimneys. Now that chimneys are mostly closed and draughts prevented (by sealing homes up tightly), condensation problems result.
  4. Building materials. If the materials used to build your home do not dry out thoroughly after the manufacturing process they can have high moisture content. One example of this is  “green lumber,” which is still wet, as opposed to kiln dry lumber, which has been dried. Mold may already be growing on such materials when it arrives at the construction site. Many builders use these materials. Another concern is green cement that has not properly cured before floors and walls are installed.
  5. Construction. Builders unfortunately do not control the weather. I'm sure many of them wish they could! They can, however, keep building materials dry and protect the building itself during construction. If this kind of protection is not provided and the building materials are allowed to get wet and are then used or sealed up into the building envelope, you can have a massive mold problem just waiting to happen.
  6. Poor ventilation can also cause molds to grow. Molds are often most severe in the corners of rooms that are external walls. This is mainly because insufficient ventilation creates pockets of stagnant air in these corners. Built-in cupboards, particularly when located against external walls, suffer from the same disadvantage. Closets, basements, and storerooms are prone to mold growth for the same reasons.
  7. Yet another source of mold growth are appliances that have standing water in them such as air conditioners, drip pans under refrigerators, humidifiers, and dehumidifiers.
  8. Two last sources that are worth mentioning here are plants that are over-watered and food left out in the open. Even a moldy orange in the fruit bowl can result in a significant release of spores.

As you can see some of these mold problems are building-related and some are to do with proper housekeeping. Once mold is set in motion it will spread to the extent that the moisture migrates. As a result of a prolonged leak, there could be many species of molds, which have colonized over time. In these situations, where there is a multicultural environment, there is a greater likelihood of mycotoxins being present. Many molds associated with water-damaged buildings produce mycotoxins.

If you do discover a mold problem, it is important to understand that mold spores can travel in several ways: they may be passively moved (by a breeze or water drop), mechanically disturbed (by a person or animal passing by), or actively discharged by the mold itself as part of its normal life cycle (usually under moist conditions or high humidity).

When mold spores land on a damp spot indoors, they usually start digesting whatever they are growing on in order to survive. Molds gradually destroy the things they grow on. Mold spores are minute and even carrying a contaminated piece of wood through the kitchen is enough to distribute countless mold spores to new locations — all ready to do their thing as soon as conditions are right.

It is important to understand that settled spores will remain dormant until sufficient moisture is present to allow them to germinate.Without moisture, mold spores are like an acorn sitting on a sidewalk — it will never grow into a tree in this spot. However, settled spores can be disturbed and can provoke allergic effects in people with mold sensitivities. It is important to use controlled demolition when remodeling to minimize the release of spores.

You cannot determine toxicity by the color of mold. “Killer black mold” (Stachybotrys chartarum) is a gross misnomer, as many black molds are of the garden-variety type 6 and not dangerous. The only way to really determine what kind of mold is present and whether it is a problematic kind or not is to enlist the help of an Indoor Environment Professional (IEP) who will give a visual inspection and then take samples which will be sent to a lab for identification. The IEP will be able to evaluate the lab results and then recommend an appropriate plan of action to fix the situation and protect your health at the same time. I recommend enlisting the help of a certified microbial remediation contractor (a mold remediator) independent of the IEP to implement this plan, to avoid any conflict of interest.


Checklist for possible sources of mold problems

  1. Moisture behind bath tiles resulting from cracks or caulking gaps.
  2. High humidity in the basement from improper dryer vent, high water table, or clogged drain.
  3. Leaking windows.
  4. Wet carpets.
  5. Drain pan under refrigerator.
  6. AC drain pan, cooling coils, and ductwork.
  7. Plant bases.
  8. Roof leaks and wet insulation.
  9. Water pipe leaks.
  10. Dampness and poor air flow under sinks.
  11. Dryer vents not connected to the outside.
  12. Corners of rooms with external walls.
  13. Cabinets and closets attached to external walls.
  14. Faulty gutters and drain pipes that direct water onto or under the building.
  15. Sprinkler systems that wet the walls or foundations.
  16. Showers and shower curtain.
  17. Ventilation fans.
  18. HVAC ducting.

To learn more about cleaning up your potential mold problems - check out our mold cleaning article. 


Stay Connected.
You've been added to our mailing list.
Thank you for signing up!
Like ecolife on Facebook & Google, and join us in the Green movement!