Mold 4. Testing

Test for mold to answer questions about what types, what amounts, and how much it matters.  Testing involves sampling, analysis, reporting, and explaining the results.

Why test Mold?

  • Test airborne mold with spore traps as the best way to find out how much we are breathing (usually done after cleanup or for more reassurance even though no growth or odor was found).
  • Test mold to test a cause/effect hypothesis (your best explanation for the moisture/mold problem).
  • Use expected test results to support your observations and hypothesis.
  • Use unexpected or inconsistent test results to form a better hypothesis; test again.
  • Testing settled surface  or carpet dust can tell about longer in the past.

Looking for Mold

  • Expect mold growth appearance after a few days as spots, then as fuzzy growth.
  • Wood rot fungus often has stringy white or brown mats on the surface, and eventually soft wood, sometimes breaking into “brown cubical rot”.
  • Use mold growth colors to help identify common types.
  • Confirm mold by its plantlike, segmented, or spore structures under a magnifier or a microscope.
  • Ignore thin, greasy, shadowy black soot deposits on cold surfaces (not mold).
  • Ignore dark stains leached out of wet wood, although it might include some mold.

Smelling for Mold

  • Use mold odor as evidence of damp mold (only when growing, no odor when dry and dormant), pointing to a source or a pathway.

Sampling for Mold

  • Sample airborne particles using Zefon Air-O-Cell spore trap cassettes, which impact particles onto a sticky microscope slide.  Follow these procedures.
  • Sample airborne mold (rarely) using nutrient in petri dishes if viable culturing is needed (can identify species better for medical diagnosis, but few will grow, and too slowly for most jobs).
  • Sample mold spores either growing (bulk) or settled (with room dust) on a surface using sticky tape lift, for microscopic analysis by direct examination.  Follow these procedures.
  • Sample total viable molds on surfaces by wiping with sterile swabs (used for kitchen sanitation).
  • Sample bulk dust into a vacuum nozzle filter cup.  Follow these procedures.

Analysis for Mold

  • Use direct examination “nonviable methodology” of spore traps to get easier sampling, faster analysis than culturing viables:
  • Advantages of direct examination:
    • Both viable and nonviable spores are identified (more than by culturing).
    • Spores of Ascospores, Basidiospores, Myxomycetes are mostly not seen with viable sampling methods, or appear as sterile mycelia.
    • Stachybotrys spores are easily identified (but are difficult to culture).
    • Counts can include other nonfungal (not mold) particles, which helps validate the test results with other dust ingredient information.
    • Spore types (both viable and nonviable) are identified, but not many species.
  • Limitations of direct examination:
    • Spores of Penicillium and Aspergillus (& others such as Acremonium, Paecilomyces) are small, round, undistinguished, and most cannot be differentiated well, so are usually reported as Penicillium+Aspergillus (mostly Penicillium).  Some experts (George Mueller, GM Labs) might separate into smooth (mostly Penicillum) and ornamented (mostly Aspergillus).
    • Spores of some species are very small, so are easily missed or undercounted
  • Identify spore types by microscope at 400X.
  • Expect to find common Penicillium, Aspergillus, Cladosporium, Alternaria, Aureobasidium, Epicoccum; maybe Periconia Ulocladium, Stachybotrys.
  • Count spores in several fields; calculate total per sample.
  • Report concentration levels of mold spores per cubic meter.

Other analyses

  • Analyze airborne mold by “viable methodology” of culturing viable spores and mycelia:
    • Collect in a dishes with different nutrients (for different molds, or for bacteria or yeast)
    • Wait about 5 days for colonies to grow enough to recognize colors & shapes.
    • Identify and count colonies from viable “units” (of spores or hyphen fragments).
    • Identify mold genus and species, and maybe some strains.
    • Report concentration levels of colony forming units per cubic meter (CFU/m3).
  • Analyze total viable molds on surfaces by wiping with sterile swabs, then growing to count total levels of colony forming units per square decimeter (CFU/dm2) of fungi (molds, yeast, and aerobic bacteria).
  • Analyze bulk dust by MSQPCR (mold-specific quantitative polymerase chain reaction), to use the EPA Relative Moldiness Index (ERMI).
  • Analyze using other labs — I recommend (see details) GM Laboratories , Microlab Northwest, and Lab/Cor.

Mold Results: Why?

  • Tell which types seem to be coming from either indoors or outdoors.
  • Explain the highest levels found indoors: unusual type? unusually high? Why were they that high vs. other samples?
  • Describe broadly the level of each indoor type, starting with and emphasizing the most abundant, such as “below”, “similar to”, “above”, or “much above” “typical clean homes or offices” (vs. spores per cubic meter in homes typically: Penicillium <400, Cladosporium <300, Basidiospores <600).
  • Tell which types came from (were higher near) a suspect source.
  • Emphasize the importance of types found that are associated with wet conditions (Stachybotrys, Ulocladium).
  • Do not use the total of molds of different types, because the total hides information about changes in population differences among samples.
  • Wetter condition molds (Stachybotrys, Ulocladium) and yeasts are less likely to become airborne.
  • Some types grow mostly outdoors; their spores are also found indoors.


  • Were any types much higher outdoors than indoors? (Expect Basidiospores & Ascospores, mostly from outdoor “mushrooms” and plant parasites.)
  • Were any types much higher indoors? (Expect Penicillium, Aspergillus, Cladosporium.)
  • Were any indoor control locations above the problem area?
  • Were any breathing zone levels much above typical levels?
  • Were those high levels even higher near the suspect source?
  • Were the levels higher with more activity/disturbance?
  • Was there some type of flag found that can be best used for clearance testing after cleanup?
  • Was Stachybotrys or Ulocladium found (typically) not? (after dried and disturbed during cleanup?)
  • What percent of the total dust particles are the mold spores? (Typically 0.3% in clean homes, or 0.9% in typically less dusty offices.)


  • Is there much nonbiological background debris that may obscure small spores?
  • Are skin flakes (a good marker for general dust) common indoors, as expected?
  • Are there many glass fibers? paint? soot?


  • Use the EPA Relative Moldiness Index (ERMI) to compare levels of types associated with water damage with those common indoors (sample settled dust into a filter cup; analyze by MSQPCR).
  • Explain mold fragments (which are not a unique pellet of information like a spore) and spore chains in terms of recent growth and disturbance.
  • Ignore Yeast, which behaves wildly differently from mycelial mold spores (and can overwhelm total counts).
  • Ignore single spores found.
  • Ignore levels 10 spores/m3 or lower indoors.
  • Avoid inflammatory words like “toxic” or “infestation”.

NEXT:  5. Mold Avoidance

©2016 Richard Knights, Blue Sky Testing Labs, Seattle,