Photograph of an antique book on philosophy - before drywall was inventedMold proof drywall ? You Must Be Kidding!

  • DRYWALL MOLD RESISTANT - CONTENTS: opinions on using mold-resistant or "mold proof" drywall or gypsum board products as a step in preventing mold growth in buildings - advice. Drywall and gypsum board standards, trade practices, & MSDS Sheets. Is the new "mold resistant drywall" a viable product?
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Guide to mold-resistant drywall: evaluation & opinion:

Using mold-resistant drywall: this article reviews the benefits and limitations of using mold resistant drywall, gypsum board, or Sheetrock(TM) (which is a trademark) as a step in building mold-resistant construction. We include a list of drywall standards and MSDS information. While mold-resistant drywall may be a good idea for some problem-prone building locations, avoiding mold growth in buildings requires more than just this product.

We also ask about the probable effectiveness of mold resistant drywall in large part because a careful reading of the manufacturer's data places very constrained limits on how this new and more expensive drywall is promised to perform.

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What are you getting if you buy the new "mold resistant" gypsum panels to use after your mold remediation project?

Mold growth pattern on drywall © Daniel Friedman

Both of the major drywall companies are now marketing drywall which is advertised as offering "mold and mildew resistance". I was excited to hear about this because drywall in buildings, when it has gotten wet or been subjected to prolonged high moisture, is a very common place for mold growth.

When a building has been wet or been subject to high indoor humidity, it is common to find problem-mold both on the visible or room-side and often on the hidden or wall-cavity side of drywall (illustrated later in this article).

Photo at left: severe mold contamination on the room-side of drywall in a wet basement. This was not a mold-resistant drywall product. But in this article we question how much better mold resistant drywall can perform under the same conditions that produced this mold problem.

[Click to enlarge any image]

First, Possibly Gouged: at a central New York mold remediation project the contractor told me that his local supplier was charging him four to eight times the cost of "regular" drywall (which he calls "sheetrock" (a trademarked name) or "gyp board" which is slang for gypsum panels.

Second, Promised very little: if the USG submittal sheet for "Sheetrock(R)" Brand Humitek(TM) Gypsum panels is any indicator, the manufacturer has given themselves an impressive escape clause. Quoting from the product limitations on this USG document, using its item numbers:

Mold-free drywall in an attic © Daniel Friedman

Photo at left: mold-free drywall in the attic of an older home. This product was also not a mold-resistant drywall material, but has performed perfectly well for several decades.

    1. Avoid exposure to temperatures exceeding 125 deg F (Translation: keep it away from your boiler flue, it's not fire-rated).
    2. Avoid exposure to excessive or continuous moisture before, during and after installation. Eliminate sources of moisture immediately. (Translation: if you put this material in an environment where mold grew on your old drywall, we're not promising that this product will perform any better. That advice is absolutely sound. See MOLD RESISTANT CONSTRUCTION.)
    3. Not suitable for use in high moisture areas such as tub and shower enclosures, gang showers, and other areas subject to direct water exposure. (Translation: you shouldn't have used your old drywall in the bathroom and you shouldn't put this new product near the tub, sink, or shower.)
    4. Non load bearing.

The moisture and mold resistance of this material is cited as "Per ASTM C473, the average water absorption for panels is not greater than 5 percent by weight after two-hour immersion."

Translation: sounds great, doesn't it? Indeed improving the resistance of drywall to moisture uptake should improve its mold resistance, as might painting it.

Really? In our OPINION, what all of this means is simple. In general we only find problem mold growth on drywall that has been subjected to excessive moisture, wetting, or actual building flooding. In other words, ordinary drywall products perform perfectly well in dry environments. Since it would appear that the producers of mold resistant drywall warn that they cannot promise anything about its mold resistance in humid or wet environments, it is difficult to understand why the extra cost for mold resistant drywall would be justified.

And what remains un-defined is "excessive or continuous moisture before, during and after installation". Just as our frustrating conversation with a hardboard siding manufacturer claims rep who told us "don't install it if it's too wet" but who would not give even the most vague hint what "too wet" means, (SIDING, FIBER CEMENT MOISTURE LEVELS ) we are left with a bit of uncertainty about the product and how it can perform.

In other words, if the building is dry you won't see problem mold growth on drywall. If the building is wet, nobody is promising you that the mold-resistant drywall will actually not become moldy.

OPINION: Use mold resistant gypsum panels with hesitation and caution

Toxic black mold, in this case Memnoniella echinata, exposed by removing apartment drywall

This product sounds like a great idea but ... considering the limitations stated by the manufacturer, I would want to see a lot more about the make-up, testing, and field-use experience of this material before I'd pay the premium suppliers are getting to provide it to your mold remediation contractor.

Photo at left: severe mold contamination (Memnoniella echinata) in the wall cavity of a drywall covered New York city apartment wall that looked perfectly clean from the wall exterior. (HIDDEN MOLD in CEILINGS / WALLS)

Anyone who has used moldproof drywall and sees what they think is mold growing on this new product is welcome to send a sample to my lab.

If your sample comes from Humitek™ or any other drywall manufacturer who provides mold-resistant drywall, we will process your sample pro-bono.

See DUST / MOLD TEST KIT INSTRUCTIONS for easy and inexpensive mold sampling procedures that work well for identifying mold or other particles found on drywall or on other surfaces.


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