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USE A FLASHLIGHT
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HIDDEN MOLD, HOW TO FIND
Hidden Mold Behind Paneling
Hidden Mold Between Framing & Sheathing
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Hidden Mold in Wall Cavities
Light colored toxic molds
Moisture Gradients and Mold
Other Places to Look for Hidden Mold
Recognizing Cosmetic Mold
Spotting Hard-to-See Mold
Use a Flashlight to Find Mold
Wall test cuts to spot hidden mold
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INDOOR AIR QUALITY IMPROVEMENT GUIDE
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Black Mold Brown Mold
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Invisible Mold
Meruliporia Mold Photographs
Recognize Cosmetic Mold
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Stuff that is Mistaken for Mold
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HARMLESS INDOOR PARTICLES
Basketball Mold Syndrome - BBMS
Black stains from soot/thermal tracking
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Black cosmetic mold
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White stuff that is not mold
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MOLD ATLAS & PARTICLES INDEX
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MEDIA BLASTING for Mold Removal
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The fact that mold is "hidden" in buildings does not mean one cannot find it. 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. Also see MOLD GROWTH on SURFACES for an index of what mold genera/species are frequently found on various building surfaces and materials and see TRAPPED MOLD BETWEEN WOOD SURFACES for a discussion of the question of need to remove mold from mated building surfaces.
© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
HIDDEN MOLD in Buildings, Insulation Mold, and Other Hidden Mold Reservoirs in Buildings
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.
In the photo at page top we see the results of a wall cut through drywall to expose wet moldy insulation, mold on the cavity side of drywall, and surprise! a leak in a pipe that the owner did not know was in her basement wall. However there was good evidence in the form of stains on the exposed side of this drywall. Look at the tan stain which is in the photo in the half-round shape directly above the wall cutout.
Don't try to investigate a building by dashing about with an axe cutting holes willy-nilly. That is an unnecessarily and inappropriately destructive approach to studying a property. But when building history, occupant complaints, or direct site observation of site and building conditions raise the level of probability of an important hidden leak or other damage, directed exploration, often with very modest means, can be very productive.
Here is a Photo Guide to Finding Hidden Mold in Buildings:
Where to look for hidden mold on and under carpeting and flooring
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Lift carpets to inspect carpet tack strips and carpet padding and carpet underside. Water stains on carpet tack strips and rusty carpet tacks on those strips are other indicators of the leak history in the area. (See the MOLDY CARPETS link at left.) Remember that mold may be present on the under-side of the carpet itself or on the top or under-side of carpet padding located below the actual carpeting. Hidden mold may be found on the floor surface below the carpeting, or even between layers of finish flooring and subflooring. We also find mold quite often on the under-side of subflooring. Look up at subfloors from basements or crawl spaces; where a wooden subfloor is installed on furring or "sleepers" placed over a concrete slab, it may be necessary to cut small test openings to explore these hidden cavities. The best place for a test cut to look for mold over an inaccessible floor or any other building cavity would be where we suspect that water has been most likely to be present, but openings may also be made in unobtrusive spots nearby, such as in a closet or under shelving where the cosmetic damage will be minimized. A Photo Guide to Use of Borescopes to Look for Mold in Building Cavities |
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Use borescopes or small test openings: in areas where we suspect leaks into building wall or ceiling cavities we may use a bore scope to peer into the cavity through an opening about the diameter of a pencil. You may not have access to this equipment but there are other useful steps that can be taken to look for hidden mold. Where there is a greater probability of leaks into a wall or ceiling, or where there are stains, we may use a larger hole saw, such as shown below where we describe the inspection of building wall, ceiling, or floor cavities. |
A Photo Guide to using a round hole saw to make test openings in building ceilings, walls or floors to look for hidden mold
Wall cavity test cuts for mold: The photo at right shows us cutting a round hole in a wall to expose the wall cavity. We cut high enough above the floor to avoid the sill plate and to give access to the wall cavity itself. We cut close to but not on top of a wall stud, so that when examining the wall cavity we can examine:
Do not fail to check all of these surfaces. It is common to find more severe mold growth on the drywall of one side of a wall cavity than on the other. This happens when water has run down one surface but not on another. When cutting a test opening to explore a wood floor installed on sleepers over a concrete slab, we use two diameters of hole saws (see photos in the next section.) First we cut a larger-diameter round hole (say 2.5") through the finish flooring using our hole saw's larger cutting blade. We remove and save the wooden plug created by this step. Second we cut a smaller-diameter round hole (say 2") through the subflooring to expose the cavity below. We examine the exposed and inner or hidden surfaces of each plug which is cut, as well as any rosin paper or other material that may be installed between layers of flooring. Finally, using a flashlight and often a borescope as well, we explore the floor cavity itself for evidence of visible mold, organic mold-friendly debris, insect activity, or evidence of leaks or flooding. |
How to Make Small Test Cuts to Check for Hidden Mold in Building Walls & Ceilings - Using a Drywall Knife
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Small homeowner test cuts in walls: Make small test cuts in drywall in areas most-likely to have been wet. Don't make a big dusty (or moldy-dusty) mess. Keep it small and clean. You may want to re-seal test openings after using them, pending cleanup or further action. Pull off floor trim at the floor/wall juncture in basements on walls suspected of harboring leakage - look on the back of the trim and on the newly exposed drywall for hidden mold growth. |
When to Make Larger Wall Test Cuts to Check for Hidden Mold in Buildings
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Larger wall cut openings: We may make a larger cut if external evidence such as staining or rot are strong suggestions of a wet, damaged, or moldy wall cavity. In the example shown you can see a water stain just above the upper horizontal line of this test cut in a basement corner. We cut the drywall because of a combination of factors that elevated the risk of hidden mold in this area:
In the wall we found evidence of a history of plumbing leaks from a drain that the homeowner did not know was even in this wall (center of the cut out area); we found evidence of a severe rodent infestation (right stud bay of the cutout area); and we found visibly wet, moldy insulation in the test cut area (left stud bay in the cutout area). |
How to Make (or not make) Random Test Cuts to Check for Mold in Building Cavities
Random wall test openings: We have little confidence in and are reluctant to simply make random test cuts in buildings. Since water can take peculiar paths through hidden openings, such as wall plate holes drilled for pipes or electrical wiring or between single pairs of studs or ceiling or floor joists, cutting a hole that does not reveal a problem is no assurance at all that no hidden mold problems exist.
When to Make Strip Cuts to Look for Hidden Mold in Building Ceilings or Walls
When there is an ongoing building complaint that makes us suspect hidden leaks or mold, if we strongly suspect a hidden mold problem but have not found its precise location, on occasion it is justified to make a "strip cut" across multiple wall studs or ceiling joists, exposing multiple wall cavities.
How, Where, & Why to Peel Back Wallpaper to Check for Hidden Mold in Buildings
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Carefully peel back wallpaper under windows where there has been leakage, or in bathrooms over and near showers. Mold often grows on paper wallpaper backing or on wallpaper glue in areas that have been wet.
Photo Guide to Finding Hidden Mold on Furniture, Bathroom Vanities, & Built-In Drawers or Shelving |
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Look for hidden mold under drawers in areas subject to spills, leaks, or dampness, such as in bathrooms and kitchens. Inspect the drawer underside and the wood flooring exposed if built-in drawers are removed completely. Moldy furniture guide: We also inspect the under-side of furniture, especially in areas that have been wet or humid. These "hidden" un-painted or un-varnished wood surfaces often support mold growth before it will be visible on the sealed or painted (and more moisture-resistant) surfaces. Game tables such as pool tables usually include un-finished surfaces on their undersides. Chipboard, and even vinyl-covered chipboard are often very friendly to un-wanted Aspergillus sp. or Penicillium sp. mold growth. |
Photo Guide to Finding Mold Under or Behind Bathroom Vanity Cabinets
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If there has been protracted leakage or spillage under built-in cabinets such as bath vanities, there may be a mold cleanup job under or behind these components. We removed this bath vanity after receiving complaints of recurrent moldy odor in this bathroom. No amount of cleaning of other bath surfaces had reduced the mold smell. A slight slope in the bathroom floor had been sending tub spillage behind this bath vanity for decades. |
What makes a lot of sense sense is to study the building carefully to decide on the building points at most risk of having been wet from leaks due to construction details or other site observations. That's where one would make a test cut.
We frequently add text and photos to this series of articles. (See "What MOld Looks Like" and "Stuff that is Not Mold" links at page left). Readers should also review Mold in Fiberglass Insulation in Buildings at our The Mold Information Center - What to Do About Mold in Buildings
Small amounts of mold can be removed simply by cleaning or removing infected materials, something most homeowners can handle -- but see the Warning Notice at the end of this article. Some mold species can make you sick.
How to Identify Hidden & Visible Molds that are Cosmetic or Harmless, or Other Low-Risk Molds
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Cosmetic-only Ceratocystis/Ophistoma bluestain mold is shown on the floor joists in the new construction framing in the photo just above. This is a harmless, cosmetic-only mold that does not damage the lumber and is not a pathogen for humans. Here's a good example of the observation that not all "black mold" is "toxic black mold". It will be totally hidden when the ceiling drywall is installed. |
The mold shown in the photograph above is plain to see during construction, but will be covered and hidden completely when the contractor installs the ceiling drywall.
One of our clients discovered this mold during a renovation and was quite concerned that a major toxic black mold reservoir had been found in the building. The client was facing a very costly mold cleanup project if this mold had to be addressed as a toxic material. Luckily this was not the case in this instance, as was easily demonstrated both by a simple inexpensive lab test and confirmed by onsite inspection of other framing details discussed at "Cosmetic Molds" linked-below.
So sometimes the mold in your house might be only a cosmetic concern. "Bluestain" or Ceratocystis/Ophistoma is common on framing lumber and we often find it in attics on the under side of roof sheathing. Unless it's in finished portions of living space where it creates a cosmetic problem, no particular action needed to address this black mold.
Detailed advice about how to determine by visual inspection alone whether or not you're probably looking at one of these common framing lumber cosmetic molds is at our Photo Guide to Cosmetic Molds.
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MOLD INFORMATION CENTER
ALLERGEN TESTS for BUILDINGS
DO-IT-YOURSELF WARNINGS
FLOODS & MOLD CLEAN/PREVENT
MOLD ACTION GUIDE - WHAT TO DO
MOLD DETECTION & INSPECTION
HOW TO LOOK FOR MOLD
WHAT MOLD LOOKS LIKE
ATTIC MOLD
BASEMENT MOLD
CARPET TEST GUIDE
CAT DANDER
CRAWLSPACE MOLD
DRYWALL MOLD
HIDDEN MOLD, HOW TO FIND
Photo Guide to Finding 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
Use of a flashlight to find mold
Wall test cuts to spot hidden mold
Light colored toxic molds
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
USING LIGHT TO FIND MOLD
HIDDEN MOLD, HOW TO FIND
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More Information on Building Diagnostic Inspections and Repairs
- How to Find and Test For Mold in Buildings - Looking for Mold - A 'how to' photo and text primer on finding and testing for mold in buildings
- Recognizing Mold: What mold looks like mold identification photos to help identify mold - choosing what to sample in buildings
- 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
- Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
- Mold Action Guide: an easy step by step outline of what to do about mold
- How to find mold without hiring anyone, for do-it-yourself'ers
- Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
- Mold Test Kits - How to Collect and Send Your Own Mold Sample to our mold testing lab
- How to find a mold inspector or test consultant: Directory of IAQ,Sick Building, Mold Allergen Testing, Building Investigation Service Providers
- Meruliporia: the house eating fungus or "poria"
- Mold Investigation Tips for Home Inspectors how to find mold, where to look, what is likely to be important. Advice to building inspectors intending to inspect or test for toxic or problematic mold indoors, mold inspection methods, and mold test methods which are valid or invalid
- Mold Risk Levels in Buildings Based on Visual Inspection - simple visual clues help decide on action
- Mold in Fiberglass Insulation© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation - DJF
- Frequently Asked Questions About Mold -- check this FAQ list & IAQ Site Map to see if you can find a quick answer to your mold concern
- When to hire a professional to inspect for toxic mold or other allergens
- Contact Us to arrange mold/IAQ building on site inspection and testing.
 InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest. |
 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 |
 Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab |
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Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
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