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What do we do when we cannot find a mold problem but we think there is problem mold in a building. Suppose an "air test" says there is problem mold indoors but you don't see where the "problem mold" is coming from? Where and How do we look for hidden mold?

Also see Mold Related Illness: Index of Symptoms and for an atlas of building molds and for more microphotographs of building mold samples observed in our laboratory, see Mold Atlas of Indoor Clinical Mold, Pathogens, Allergens & Other Indoor Particles. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links show where you are in our document & website.

Where to Look When You Cannot Find the Mold Problem in a Building

Where to look for "Invisible Mold" in Buildings - important mold reservoirs that cannot be detected by visual inspection

Results of a small test cut to check for hidden mold

Of course some important problematic mold reservoirs may be hidden inside building cavities where you won't see them without making a test cut in just the right place. We find these problems by inspecting "by context", that is, we decide where to make an invasive test cut by studying where leak or moisture problems have been or are likely to have been on a building.

This photo shows the hidden interior side of drywall on the test cut we made using the hole saw shown at the top of this page. The red material was a yeast which accompanied toxic mold which we confirmed was present in this wall cavity.

What's important is the development of a strategy for just where to make such test cuts to look for hidden mold. Random test cuts to screen a building for mold are unreliable.

Some other critical indoor mold problems may be on an exposed building surface or material, but the mold may be totally invisible to the naked eye. Such "hidden in plain sight mold" can be detected by a combination of common sense in recognizing mold-friendly materials and mold-producing conditions.

Exposed insulation may be mold contaminated

For example, fiberglass insulation in the ceiling over a flooded basement or crawl space is highly suspect. In some cases it's more economical and sensible to simply replace suspect material than to spend on testing it for mold contamination.

But where large areas or large expense would be involved, special testing methods can determine whether insulation or other mold reservoir materials are indeed mold-contaminated. We use a combination of vacuum pump and sampling cassettes to examine suspect building insulation.

See Mold in Fiberglass Insulation for details of the occurrence of mold contamination in building insulation, and see  Vacuuming building cavities as a screen for building mold as well as Vacuuming exposed insulation for finding mold-contaminated fiberglass.

Here is a photo taken in our laboratory when we examined our sample of insulation which we suspected would be mold-contaminated. You can see extensive mold contamination of at least two types, Penicillium/Aspergillus spores and spore chains and darker fungal spores which are probably a species of Cladosporium sp. This insulation looked "clean" to the naked eye, but by context we suspected it would be a problem reservoir of mold. Moldy fiberglass insulation is often missed by casual or inexperienced mold inspectors. The presence of spore chains confirms that we had active mold growth nearby if not in the insulation itself.

Making a larger wall test cut to check for hidden mold Here we made a larger test cut in mold-suspect drywall because we saw a leak stain on the exposed surface. Even though there was no mold on the exposed side of this wall, the water stain led us via this test cut to discover a leaky drain pipe that was previously unknown. We would not make a cut like this unless there was external evidence of probable leakage into this cavity; a borescope might have found this problem too, though views through such instruments are quite limited and do not permit full examination of all materials and surfaces. Notice the evidence of mouse activity at the right end of this test cut?

Removing Wallpaper to Check for Hidden Mold In our daughter's condominium we peeled down clean-looking wallpaper because we saw evidence of a history of leaks into the wall cavity at the window sill. Even though there was no mold on the exposed side of this wallpaper, the water stains led us via this test to discover an area of Stachybotrys chartarum that was worth removing. We often find mold growth behind wallpaper where there has been leakage or high moisture, including wallpapers used in bathrooms. Beware: some antique wallpapers which may be attacked by mold growth can cause the release of poisonous arsenic into the local environment.

Hidden Mold Under Furniture Drawers or Built-in Drawers Simply pulling out a drawer may reveal problem mold growth. In this case we found this by pulling out the bottom draw of a built-in storage chest in a bathroom in an older home. we have also found Aspergillus sp. colonies growing on the un-finished underside of furniture and game tables.

Hidden Mold Behind Wall Paneling We pulled down this bathroom paneling even though it's exposed side looked very clean, because other clues indicated that there had been a history of floor flooding in this area.

Hidden Black Toxic Mold Behind Drywall

We made the test cut you see in the photo at left above, even though the architect had directed the mold inspection and testing to be performed in a completely different building area.

That's because we saw water-damaged flooring and because occupants of this area were complaining of severe respiratory and eye irritation. We had to push insulation aside to show the black mold just visible in this photo on the cavity side of the opposing drywall. Our lab test indicated that we'd found Memnoniella echinata (a very close relative of Stachybotrys chartarum) which we find quite irritating.

The second photograph above shows how extensive the mold growth was when the lower wall cavity was cut away. This mold contamination had spread on 100 linear feet of wall in this area due to an air conditioning leak which drained into the channel formed by the steel u-channel used as a sill plate for this steel-stud wall.

Be sure to review our mold-detection guides & articles on where and how to look for hidden mold problems in buildings:

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website

• HIDDEN MOLD, HOW TO FIND
• INSULATION MOLD a photo tour of other places to look for hard-to-spot mold
• Mold in fiberglass insulation in crawl spaces
• FIberglass in Indoor Air, HVAC ducts, and Building Insulation
• USING LIGHT TO FIND MOLD
• HOW TO LOOK FOR MOLD

MOLD: A COMPLETE GUIDE TO MOLD INSPECTION,
  TESTING, CLEANUP & PREVENTION
MOLD ACTION GUIDE - WHAT TO DO ABOUT MOLD
MOLD APPEARANCE - WHAT MOLD LOOKS LIKE
  Black Mold  Brown Mold
  Green Mold  Red Mold
  Yellow Mold  White Mold
  Invisible Mold
  Meruliporia Mold Photographs
  Recognize Cosmetic Mold
  Recognize Harmless Black Mold
MOLD APPEARANCE - STUFF THAT IS NOT MOLD
  HARMLESS INDOOR PARTICLES
    Basketball Mold Syndrome - BBMS
    Black stains from soot/thermal tracking
    Black stains from animals
    Black cosmetic mold
    Efflorescence & brown deposits
    Efflorescence & white or brown deposits
    House dust
    Pollen
    Sprayed foam insulation
    White stuff that is not mold
    Wood sap

More Information on Building Diagnostic Inspections and Repairs

• Looking for Mold Procedure: what mold is often found where in buildings - simple technical presentation
• How to Look For Mold, List of Articles: Hiring a Mold or IAQ Consultant, Getting a Remediation Plan
• Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens
• Recognizing Allergens: What various indoor allergens look like - identification photos to help identify pollen, dust mites, animal dander, toxic or allergenic mold - Common Mold and other Allergens, Irritants, Remedies & Advice
• Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
• Allergens: what they look like in buildings
• Animal Allergens: Dog, Cat, and Other Animal Dander - Cleanup & Prevention Information for Asthmatics and regarding Indoor Air Quality.
• Mold in Fiberglass Insulation© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation - DJF
• Mold Investigation Tips for Home Inspectors how to find mold, where to look, what is likely to be important. Advice to building inspectors intending to inspect or test for toxic or problematic mold indoors, mold inspection methods, and mold test methods which are valid or invalid
• Mold Test Kits - How to Collect and Send Your Own Mold Sample to our mold testing lab
• Meruliporia: the house eating fungus or "poria"
• Mold Central: indoor air quality investigation case histories, key links what to do about mold and indoor allergens - our Fear of Mold "Mycophobia" WebLog-Blog.
• Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
• Rot concerns in buildings-some building mold such as Meruliporia incrassata "Poria" risks serious rot and hidden structural damage
• Frequently Asked Questions About Mold -- check this FAQ list & IAQ Site Map to see if you can find a quick answer to your mold concern

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