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This article discusses how, why, when, and where to make wall test cuts to find and test for hidden mold contamination or growth in buildings. 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. See MOLD RESISTANT DRYWALL for a discussion of that product type as well as a list of drywall or gypsum board industry standards and drywall product MSDS sheets. Moisture Gradients and Mold discusses the variation in type of mold growth found on drywall or gypsum board at different heights above a wet floor.

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Making wall test cut openings to spot hidden mold

This article on mold inspection and testing discusses the use of test cuts in building surfaces to explore building cavities for hidden mold. Since even small cosmetic damage to buildings is something to avoid when possible, we also discuss how to decide when a test cut is justified, and now to explore building cavities with the minimum damage. This document is part of a longer article which 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.

Unless a building area is already visibly damaged or moldy, we proceed with as little damage or "invasiveness" as possible. Often no invasive cuts are needed to see into a building cavity. Text and photo illustrations in this section are roughly in order of degree of invasiveness.

Often an experienced inspector who knows where to look, can reach very reliable conclusions about hidden mold with no damage to a property at all. Or we can perform non-damaging invasive inspection such as the careful removal of trim for further inspection.

Use of a bore scope to inspect building cavities

Photos demonstrating use of a hole cutter and drill to explore buildings for hidden mold

We use several sizes of hole cutter bits to explore areas where building history or visual clues suggest a high probability of hidden mold growth between plies of building material. Examples include buildings which have been "renovated" by the installation of additional layers of drywall. The second photo (above right) shows that pink and other colored mold was found growing on the hidden or cavity side of the drywall where we made this cut. The building had been exposed to prior leaks into wall cavities from the floor above. A "water extraction" company had cut holes along the bottom of the wall in each stud bay to, as they claimed, extract the water. I have never once found this approach successful. There was no air circulation throughout the wall during the drying procedure, and worse, the process was begun too late after the leak event, and worst still, no one inspected to evaluate the effectiveness of the procedure. After the water extractors left a renovation contractor was engaged to wash and paint all of the interior wall and ceiling surfaces. Most of them were badly mold-contaminated on their hidden side and had to be removed for proper mold remediation and cleanup. The photo at above 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: The cavity side of drywall plug which was removed, checking it for visible mold The condition of insulation in the wall cavity - if any. It may be necessary to vacuum-test wall insulation to test for mold since fiberglass insulation can be moldy but look quite clean. See Mold in Fiberglass Insulation for details of the occurrence of mold contamination in building insulation, and see  Vacuuming building cavities as a screen for building mold as well as Vacuuming exposed insulation for finding mold-contaminated fiberglass. The condition of nearby upper surface of horizontal sill plates to check for mold growth or evidence of leaks The condition of nearby vertical surface of a wall stud to check for visual evidence of mold growth or leaks The condition of the wall cavity-side of the opposing drywall or exterior wall sheathing. 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.

How to Find or Test for Inter-ply mold, between layers of building materials

Larger Drywall test cuts to check for hidden mold contamination

Where we have justification to proceed we may cut a 2" x 3" hole in drywall to peer into a wall cavity. This opening, like the plug cut openings discussed above, is trivial to patch in drywall or plaster, but permits a more reliable inspection of the building cavity interior than a borescope. Where damage is already extensive, there is nothing lost, no material to preserve, and a still larger opening may be cut, or multiple openings, in order to confirm the extent of contamination and thus the extent of demolition and mold cleanup needed.

Memnoniella echinata - a toxic black mold in a wall cavity: During an investigation of a high-rise apartment in a large U.S. city, I was asked to evaluate black mold visible on basement floor joists in a kitchen. Our mold inspection procedure includes a screen of the entire living unit which in this case was a large multi-room apartment. At the far end of the apartment, remote from the kitchen and its leaks and mold, I found evidence of other leaks into and below an expensive cherry-wood floor. We traced leaks to an air conditioning wall unit whose condensate was draining into the floor rather than into its drain. The photo (left) shows our initial test cut into the wall cavity. The next photo below shows a closeup of the cavity interior.

We chose an area to make a "test cut" into the wall cavity where we thought there had been the most water exposure. The result is in the photo you see above - there was black mold in the wall cavity on the hidden surface of the drywall. A simple laboratory test confirmed what our nose and throat were suggesting at the inspection - this was a particularly irritating mold, which we identified in our lab as Memnoniella echinata.

My work plan for this New York City apartment included an expansion of the original scope to cut open the lower drywall around the room where our test cut identified this problematic mold. I asked the remediator to continue removing drywall until there was at least a 24" clear margin of no visible mold.

The result was dramatic - water had run in the steel channel formed by the metal sill plate, and had followed the wall around the apartment, producing a significant reservoir of Memnoniella echinata or "black mold" which needed to be removed. (In case you missed it, it is complete nonsense to assume that "black molds" are always a problem and even more erroneous to include light colored and hard to see molds which often are a more significant hazard in buildings.)

Another "toxic black mold", Memnoniella echinata is particularly toxic and irritating. It's a member of the Stachybotrys family but unlike Stachybotrys chartarum, a sticky spore that tends to stay in its place, M. echinata is more easily airborne and I often find it in the air when it's growing in the building. It's more of a problem than its famous brother.

The photographs provide a second warning: a small amount of mold on the visible side of a wall [Memnoniella wall] may be a clue that there is a much bigger problem inside the wall cavity. In the first photo you are looking into a small 3" x 3" opening I made to see conditions in the wall cavity. Don't do this if at risk people are around as you may be spreading spores in the air.

This photo shows the growth pattern on the cavity face of drywall on the opposite side of the drywall from where we cut and removed a larger section of drywall during remediation. You can see that the Memnoniella echinata exhibits an odd growth pattern on the wall which maps the areas of contact or non-contact of wall insulation with the paper drywall surface in this cavity.

This photo shows the extent of mold growth which had been hidden in the wall cavity after the remediation contractor cut away one side of the drywall as I had asked. You'll see that a large area of moldy drywall was involved, and that the remediation project needs to expand to include removing the opposing wall drywall and thus other rooms in the apartment.

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HIDDEN MOLD, HOW TO FIND
  Hidden Mold Behind Paneling
  Hidden Mold Between Framing & Sheathing
  Hidden Mold in Flooring & Subflooring
  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

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.

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