Photograph: Mold under carpeting on tack strips indicate history of water entry, suspect moldy carpet - Daniel Friedman Mold Sampling & Mold Testing Mistakes to Avoid - surface tests

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Mold test mistakes: this document describes how to avoid common mistakes people make when trying to find mold and test for mold in buildings, such as testing only the "black mold" on surfaces or relying only on air tests to screen buildings for problem mold.

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Mold and Indoor Air Quality Test Mistakes: Common Mold Surface Sampling and Other Mold Testing Errors

Looking for Mold in All the Wrong Places

These mistakes amount to collecting mold test samples in the wrong place, or failing to collect mold test samples in other important places.

  • Looking just for "black mold": Sampling the "scary toxic black mold" on drywall low on the wall while failing to observe the light-colored but more airborne and thus harmful molds such as Aspergillus sp. or Penicillium sp. growing higher and less visibly on the surface. See What mold looks like in a home
  • Using bad lighting: Sampling the "easy to see" mold and missing the "hard to see" mold without first looking carefully with a flashlight. See Using proper lighting to see important mold contamination in buildings
  • Bad choice of test surface: Sampling inorganic surfaces like concrete when nearby organic surfaces like drywall paper or wood paneling are present.
  • Testing Harmless Particles: Sampling things that are obviously not mold and not harmful particles. See Stuff that is Not Mold

Looking for Mold in All the Wrong Ways

  • Wrong mold test methods: Relying on screening "mold tests" such as "air tests", mold swabs, or mold cultures, to alone indicate the presence or absence of a mold problem in a building. None of these is reliable when used in place of or without a careful and expert visual inspection and each of which has severe methodological errors and variability in results.

  • Inspecting Easy Areas: Looking only in the easy to inspect areas - such as the living space or attic, and ignoring the crawl space.

  • Overemphasis of Attics Overemphasizing attic mold - where conditions such as condensation often produce less-problematic Cladosporium sp. molds which do not as easily move down into the living area. But do not ignore attics completely and especially do not ignore attic knee wall areas outside bedrooms such as in a cape cod style home.

  • Under-Inspecting Crawl Spaces: Failing to inspect crawl spaces - where conditions are often conducive to problem mold growth, especially when people are concerned about or may have found problem mold in other building areas

  • Ignoring Wall & Ceiling Cavities: Ignoring building cavities - which can, depending on wall or ceiling penetrations and the nature of air movement in a particular building, contain significant reservoirs of problem mold. Some experts opine that mold in cavities never affects building occupants. Our own field investigation has traced high levels of indoor airborne Aspergillus sp. to non-visible reservoirs in fiberglass insulation, so I would not ignore this possibility.

  • Omitting Insulation Ignoring non-visible but significant mold contamination in building insulation. Tape sampling is not useful for porous materials like insulation. We have devised special methods for screening such substances.

There are lots of other errors and inaccuracies that can confound "testing" buildings for mold, such as relying on air sampling or cultures alone, i.e. "testing" rather than performing a thorough visual inspection (by an expert who knows where to look), and obtaining a building leak history.

Classes of Testing or Statistical Errors Applied to Mold or Other Environmental Tests, Inspections, Reports

At ENVIRONMENTAL TEST ERROR TYPES we explain in more detail the classes of testing or statistical errors and how in a practical sense they appy to mold or other environmental inspection, testing, lab and reporting procedures. Type 1 and Type 2 errors are defined along with practical examples taken from building inspection and testing for mold contamination.

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