How moisture tests do or do not indicate hidden mold contamination: this article provides an explanation of An explanation of the relationship between level of moisture and mold growth in common building materials like drywall and paneling. The photo at page top shows three different mold genera/species, each occurring at a different elevation on this basement wall.

The probable reason for these distinct areas of growth was that water on the basement floor soaked the bottom section of drywall while upper sections were less wet, each attracting a different mold genera and species.

Moisture Gradients and Mold Growth on Drywall and Other Building Surfaces

This document describes how to find mold and test for mold in buildings, including how and where to collect mold samples using adhesive tape - an easy, inexpensive, low-tech but very effective mold testing method.

This mold inspection procedure helps identify the presence of or locate the probable sources of mold reservoirs in buildings, and helps decide which of these need more invasive, exhaustive inspection and testing.

This section explains that because different mold genera/species will grow on the same building material at different moisture levels, it is easy to make a mistake in inspecting or testing mold in buildings by ignoring the light-colored but more problematic molds that are often found higher on drywall above the more obvious "black mold" people see there. At MOLD LEVEL REPORTING we comment further on errors caused by failure to select a properly-representative area of a surface when collecting mold or dust samples.

Keep in mind that different molds like different moisture, temperature, and food.

One reason that S. chartarum has been "over-reported" as a problem in some studies is that the field "experts" didn't look for lighter molds, and maybe they didn't even carry a flash light.

The photo (left) shows three tape samples being taken from different heights on a laundry room wall. Three different mold species were found, one in each area. Only the lowest black mold was obvious.

Watch out:  In this wall test of three molds which were growing quite close together, I've marked each tape sample so that you can see where it was on the wall.

#1 =Stachybotrys chartarum,

#2 = Ulocladium chartarum,

#3 = Aspergillus sp.. - it is this third mold which, in a larger quantity, would be airborne and more likely to bother building occupants.

Yet nearly 100% of home owners and 80% of industrial hygienists and 90% of home inspectors who send mold samples to our lab are going to tape-sample only the "dark mold" on this wall.

Why are there three different genera/species on this drywall? Most likely because each of them prefers a different moisture level in the paper which they're digesting.

I can generally track the mold genera up the wall as a function of the moisture gradients in the wall. When a wall has been wet because of wet floor conditions, the drywall and in-cavity wall insulation will be wettest at the wall bottom.

Be sure to review our notes above on use of lighting at Use of a flashlight to find mold since if you don't know exactly how to use a flashlight, as simple as it seems, you're not going to find important light-colored molds in buildings.

See HIDDEN MOLD in CEILINGS / WALLS for a discussion of mold hidden in wall cavities. See SAMPLING DRYWALL for a discussion of mold on drywall.

Also see MOLD GROWTH on SURFACES for an index of what mold genera/species are frequently found on various building surfaces and materials.

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Continue reading at HIDDEN MOLD, HOW TO FIND or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• MOLD SAMPLE POINT CHOICES
• MOLD TEST PROCEDURES
• MOLD TEST vs MOLD INSPECT
• MOLD TESTING & SAMPLING MISTAKES
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