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How to find hidden or hard-to-see mold in buildings: as we detail in this "how to" article, the fact that mold is "hidden" in buildings, such as inside a wall cavity, does not mean one cannot find where the problem mold is located.

We look by context: where do we see leak stains, or where do we see building practices most likely to have produced a hidden leak or moisture problem? Ice dam leaks in walls, hidden plumbing leaks, roof spillage by the foundation, are all common clues that often track to a wet building wall or ceiling cavity and from there to a hidden mold problem which may need to be addressed.

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 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.

Also see FIND MOLD in BUILDINGS, HOW TO and see MOLD GROWTH on SURFACES for an index of what mold genera/species are frequently found on various building surfaces and materials, and see Mold Related Illness: Index of Symptoms and finally, 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. And MOLD BY MICROSCOPE shows what mold looks like under the microscope.

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Spotting Hard-to-See Mold on Paneling in the Living Area

USING LIGHT - Using proper lighting to see important mold contamination in buildings

How and where you shine light is of crucial importance when looking for mold in buildings. Light-colored mold such as some members of the Aspergillus sp. and Penicillium sp. groups are often the dominant problem-mold in buildings but these offenders are often missed by a casual inspection because they can be hard to see on surfaces.

You need a bright flashlight and you need to know how to use it. Shine the light along the surface being examined, not straight at it. As you'll see in the mold photographs below, using your light carefully can make a big difference in what mold you find and where you find it. Just looking for "black mold" risks missing the important mold in a building.

Light colored toxic mold on paneling is not visible because light is being shone directly onto the wainscot wood paneling surface.

Now try shining a light along the surface - this easily shows the white mold colony.

The point of these illustrations is to demonstrate that "hidden mold", like the purloined letter, may in fact be hiding in plain view - you just don't know how to see it.

Is Toxic Black Mold the Only Mold To Worry About in Buildings?

In short, no, absolutely not. Here are some details:

Recent news articles have made some people terrified at the mere mention of "toxic black mold" such as "Stachybotrys chartarum." Actually it is common to find Stachybotrys chartarum in small amounts in houses where there has been prolonged leakage or water entry. It's a toxic mold that should be removed.

But don't assume that anything and everything black on a building wall is a highly toxic mold. Some black stuff is not mold at all. See STUFF THAT IS NOT MOLD for details of black stains or debris on walls that have no mold hazard whatsoever.

Other common mold species look black but may be of low or no toxicity. For example, Chaetomium globosum has been reported to be allergenic rather than toxic. Cladosporium sphaerospermum is often found growing indoors on bathroom tile or refrigerator gaskets. It's a member of the most common mold family, Cladosporium, the "universal fungus." It can look pretty "black" on some surfaces.

Still other black molds found in buildings are completely harmless. See Recognize Cosmetic Mold and  Recognize Harmless Black Mold for details about these cosmetic molds and easy ways to spot some of them with no testing whatsoever. Just common sense can tell you that some molds have been on a surface since the time of construction.

Finally, there are plenty of highly toxic or highly allergenic or irritating molds found in buildings that are not black or even dark, especially including most members of the Aspergillus sp. and Penicillium sp. families. See  Light colored toxic molds for details.

Is it Possible to Identify a Mold Just by Looking At It On a Building Surface?

Can you tell what genera or species a mold is that's growing on a surface just by the naked eye?

No. Though I've inspected and tested so many molds on so many surfaces that like a bird watcher, I know what's likely to be present in a given habitat. (Refrigerator gasket mold is usually a Cladosporium, often C. sphaerospermum and mold growing on window muntins will be a genera/species tolerant of UV light. A normal person can't do this, though a mold investigator and a few mold remediators with plenty of experience can make a reasonable guess. (Such guesses are not always right.)

You cannot determine the mold genera and species just by looking at mold on the wall. Skip those do-it-yourself mold test kits that rely on culture or settlement plates. The methods the kits use are fundamentally inaccurate and in a few cases so are their laboratories. (90% of mold species will not grow on culture media.)

For small mold problems, spend your money on some soap and water instead.

For larger mold contamination problems hire an expert to survey your home, or send your own mold sample to a competent testing laboratory. The services of an experienced mycologist or aerobiologist are necessary to know what you've got. (C)DJF Copyright protection trap.(C)Daniel Friedman

Questions & Answers regarding this article

Questions & answers about how to find hidden mold in buildings, both on exposed surfaces but hard to see and mold hidden in building cavities, insulation, or other areas.

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• Additional technical contributors & reference sources for this article are listed below.

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MOLD INFORMATION CENTER
MOLD DETECTION & INSPECTION
HOW TO LOOK FOR MOLD
  CHOOSE SAMPLE POINT
  SAMPLING DRYWALL
  MOLD TESTING & SAMPLING MISTAKES
  FLASHLIGHT HELPS FIND MOLD
WHAT MOLD LOOKS LIKE
ATTIC MOLD

BASEMENT MOLD
BASEMENT MOLD WATER IMPACT
CARPET TEST GUIDE
CAT DANDER
CRAWLSPACE MOLD

DRYWALL MOLD

HIDDEN MOLD, HOW TO FIND
  PHOTO GUIDE to FIND HIDDEN MOLD
  Hidden Mold Behind Paneling
  Hidden Mold Between Framing & Sheathing
  Hidden Mold in Flooring & Subflooring
  Hidden Mold in Wall Cavities
  Spotting Hard-to-See Mold
  Wall test cuts to spot hidden mold
  LIGHT AIM FINDS MOLD
  Light colored toxic molds
  LIGHT, flashlight to find mold
  Moisture Gradients and Mold
  Other Places to Look for Hidden Mold
INSULATION MOLD
ITCHY FABRICS
MOLD BY MICROSCOPE
MOLD ON DIRT FLOORS
MOLD on or in CARPETS
STAINS on INDOOR SURFACES: PHOTO GUIDE
STUFF THAT IS NOT MOLD
  HARMLESS INDOOR PARTICLES
  THERMAL TRACKING STAINS
USING LIGHT TO FIND MOLD

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
• Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.
• Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
• "A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
• US EPA - Mold Remediation in Schools and Commercial Building US EPA
• US EPA - Una Breva Guia a Moho - Hongo - en Espanol

Allergies, Allergens, Allergy Testing in Buildings - References & Products

• Air Conditioning System Blower Fans & Filters Cascading for Optimum Indoor Air Quality
• Allergen Tests in Buildings advice about how to test, what to look for, in evaluating the level of dog, cat, or other animal allergens in a building
• "IgG Food Allergy Testing by ELISA/EIA, What do they really tell us?" Sheryl B. Miller, MT (ASCP), PhD, Clinical Laboratory Director, Bastyr University Natural Health Clinic - ELISA testing accuracy: Here is an example of Miller's critique of ELISA http://www.betterhealthusa.com/public/282.cfm - Townsend Letter for Doctors and Patients
  The critique included in that article raises compelling questions about IgG testing assays, which prompts our interest in actually screening for the presence of high levels of particles that could carry allergens - dog dander or cat dander in the case at hand.
  http://www.tldp.com/issue/174/IgG%20Food%20Allergy.html contains similar criticism in another venue but interestingly by the same author, Sheryl Miller. Sheryl Miller, MT (ASCP), PhD, is an Immunologist and Associate Professor of Basic and Medical Sciences at Bastyr University in Bothell, Washington. She is also the Laboratory Director of the Bastyr Natural Health Clinic Laboratory.
• Allergens: Testing for the level of exposure to animal allergens is discussed at http://www.animalhealthchannel.com/animalallergy/diagnosis.shtml (lab animal exposure study is interesting because it involves a higher exposure level in some cases
• Allergens: WebMD discusses allergy tests for humans at webmd.com/allergies/allergy-tests
• Animal Allergens: Dog, Cat, and Other Animal Dander - Cleanup & Prevention Information for Asthmatics and regarding Indoor Air Quality.
• Atlas of Mold Related Illness Symptoms & Complaints - long list of both documented, studied mold related illness, and complaints ascribed to mold contamination or allergens in buildings
• Cat Dander: how to inspect and test a building for past or current presence of cats, cat hair, cat dander, and cat allergens
• Clinical Atlas of Mold Toxicity - An Online Description of Toxic, Pathogenic, Allergenic Fungi, Fungal Diseases
• Fiberglass Insulation Contains Mold© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation
• Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
• Mold Action Guide detailed guide on finding, removing, and preventing indoor mold contamination
• Odors, Odor Detection, Smells, & Gases how to find and identify sources of noxious or toxic odors and gases
• Other environmental risks, Our much longer list: Asbestos, carbon monoxide, electromagnetic fields, etc.
• Ozone: The Use of Ozone Indoors for Control of Odors and Mold Removal in Buildings: A Summary of Hazards and False Claims.
• Pollen Allergens: identification, plant pollen and indoor air quality
• Products to Reduce Mold & Allergy Problems to reduce indoor mold or allergen levels: air cleaners, air purifiers, dust mite covers, vacuum cleaners, crawl space vents
• 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
• Rodent control issues, including dander, fecal, and urine contamination of Buildings and Building insulation are discussed at our
• Sewage and Septic backup contamination in Buildings: inspection, testing, remediation, & references to expert sources
• Action Guide: What to do about mold, mildew, and other indoor allergens
• ...

Mold Contamination Testing, Cleanup, Prevention: references & products

• The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
• Aerobiology, Building Science, Microscopy, & Laboratory References, an extensive technical bibliography
• Allergens: what they look like in buildings
• Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
• Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon)
• Atlas of Mold Related Illness: Index of Symptoms and health, physical, neurological, psychological, and other complaint which people suspect may be mold or building-related.
• Atlas of Indoor Mold, Online Clinical Mold Atlas, Toxins, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
• Black Mold that is Harmless Photos of recognizable, usually harmless black mold on wood, bluestain, ceratocystis, ophistoma
• Building Floods: quick steps after a building flood or plumbing leak can prevent costly mold contamination
• Classes of Mold: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
• Clinical Mold References - Detailed bibliography of mold reference texts
• "A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
• "Disease Prevention Program for Certain Vegetable Crops," David B. Langston, Jr., Extension Plant Pathologist - Vegetables, University of Georgia (PDF document) original source: www.reeis.usda.gov/web/crisprojectpages/209797.html
• "Disease Prevention in Home Vegetable Gardens," Patricia Donald, Department of Plant Microbiology and Pathology, Lewis Jett
  Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
• "Management of Powdery Mildew, Leveillula taurica, in Greenhouse Peppers," Ministry of Agriculture and Lands, British Columbia - Original source: www.agf.gov.bc.ca/cropprot/peppermildew.htm
• Environmental Health & Investigation Bibliography - our own technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
• Fiberglass: Mold in Fiberglass Insulation© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation - DJF
• Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
• Fungi, Identifying Filamentous, A Clinical Laboratory Handbook, Guy St-Germain, Richard Summerbell, Star Publishing, 1996, ISBN 0-89863-177-7 (English) (buy at Amazon)
• Looking for Mold Procedure: what mold is often found where in buildings - simple technical presentation
• Meruliporia: the house eating fungus or "poria"
• Mold Action Guide: Step-by-Step Instructions, What to do about mold, mildew, and other indoor allergens
• MOLD APPEARANCE - WHAT MOLD LOOKS LIKE Photos of what mold looks like in buildings
• MOLD APPEARANCE - STUFF THAT IS NOT MOLD Photos of NOT-mold material that is sometimes mistaken for mold
• MOLD ATLAS & PARTICLES INDEX, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
• MOLD BY MICROSCOPE Mold under the microscope - photo identification of the most common indoor molds found in buildings
• Mold FAQs Answers to Most Questions about Indoor Mold, Mold Related Illness, Mold Cleanup, Mold Prevention
• US EPA: Mold Remediation in Schools and Commercial Building US EPA
• Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens
• Mold Test Kits - How to Collect and Send Your Own Mold Sample to our mold testing lab or to any mold lab you wish
• Most Common Indoor Molds Found in Buildings, A Table of
• Mycology, Fundamentals of Diagnostic, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6 (buy this book at Amazon)
• 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
• US EPA: Una Breva Guia a Moho - Hongo - en Espanol

OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold

Mold or allergens may not be the only or even the main indoor environmental contaminant. Don't let media attention to mold cause so much enviro-scare fear that other, possibly more urgent hazards go un-addressed.

• Fiberglass building insulation and HVAC duct work insulation hazards
• Sewage and Septic backup contamination in buildings: inspection, testing, remediation, & references to expert sources
• Other environmental risks: Asbestos, carbon monoxide, electromagnetic fields, environmental illness, fiberglass, MCS - multiple chemical sensitivity, toxic gases, etc
• Indoor Gas Sampling Plan for Residential Buildings lists a number of toxic indoor gases which we test for, depending on the building complaint and building conditions
• Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
• Pet control - if you can't say goodbye to your bird, cat, dog, guinea pig, hamster, tropical fish, then limit the areas they occupy and limit the airflow from that area to sleeping or other areas of the building, use allergenic bedding, eliminate wall-to-wall carpeting, improve housecleaning including use of a HEPA-rated vacuum cleaner. For more details see our article Dog, Cat, and Other Animal Dander - Information for Asthmatics and Indoor Air Quality
• Rodents, Mice, Squirrel Control - I find high levels of mouse and rodent dander, fecal dust, and urine-contaminated dust in some buildings, and high levels of these materials in building insulation in those locations. If you have a mouse problem, particularly if mice and their waste (fecals or urine) are contaminating the building HVAC or building insulation, may need both steps to clean up or remove infected materials and steps to stop an ongoing rodent problem. If squirrels are a problem, the cleanup needs to include closing off entry openings into the building. Get some help from a licensed pest control expert.