Photograph of Making a test cut to look for mold in a building wall cavity How to Find Hidden Mold Reservoirs in the Home - a guide detection of mold allergens
     


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How to find hidden mold contamination: 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?

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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

Wall Cavity Side of a test cut shows hidden mold

Also see MOLD RELATED ILLNESS SYMPTOMS and for an atlas of building molds and for more microphotographs of building mold samples observed in our laboratory, see MOLD ATLAS & PARTICLES INDEX.

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.

Clean  looking insulation in a basement may be a bad mold reservoir

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 cavitiesas a screen for building mold as well as VACUUM TEST INSULATION CONTAMINANTS for finding mold-contaminated fiberglass.

Microscopic photo of mold in fiberglass insulation

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.

Wall test cut reveals moldy insulation and drywall

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.

Wallpaper peel down reveals hidden mold

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

Mold under furniture 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

Mold behind paneling in a bathroom

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

Memnoniella echinata toxic black 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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