Photograph: Mold under carpeting on tack strips indicate history of water entry, suspect moldy carpet - Daniel Friedman How to Find and Test for Moldy Carpeting in Buildings

  • CARPET ODOR & MOLD TESTS - CONTENTS: How to recognize, test, and deal with moldy carpeting. How to find mold hidden under carpets or carpet padding. When should wet or moldy carpeting be removed from a building? Should moldy carpeting be lab-tested? When to test carpets for mold contamination? When -not to bother testing carpeting for mold contaminationn.
  • POST a QUESTION or READ FAQs about testing carpeting or carpet padding for mold contamination

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Guide to moldy carpets or rugs:

Inspection & test procedures for moldy or smelly indoor carpeting & rugs. This article describes how we inspect, test, and cure moldy carpeting or rugs. We discuss the risk of hidden mold under carpeting and in carpet padding.

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MOLDY CARPETING - in buildings, how to recognize allergenic or mold contaminated carpets and rugs

Photograph: Moldy carpeting - Daniel FriedmanWhile you may see mold on carpeting in unusually severe cases, carpet, especially wall-to-wall carpeting can be a reservoir for hidden mold, mite fecal, pet dander, rodent dander, fecals, and dust, bacteria, and other allergens, pathogens, and irritants even though you cannot see anything suspicious on the carpet. Here are some warning signs that carpeting may be an IAQ problem source in a building:

  • Carpets which are visibly moldy such as in the photo above - these need to be discarded.
  • Carpets that have been wet such as by basement water entry, a plumbing leak, roof leak, sewer line backup. If wall-to-wall carpeting has been wet it probably should be removed and disposed-of.

    There are services which will remove wet carpeting and clean it for reinstallation. If wet carpeting is removed and cleaned and dried in 24-48 hours it might have a chance - I'm waiting for more field test data before I recommend this approach. If carpet was wet and stayed wet it's history. Area rugs can often be professionally cleaned and salvaged.

    If in a room where the entire floor is covered with a large area of wall to wall carpeting, and just a very small area of your carpeting has become wet or moldy, it may be more practical to cut out the damaged, wet, moldy section, plus 12" past all visible wet or damaged area, replacing or patching that section. If you can live with the cosmetic defect of imperfectly matched carpeting the cost will be much less than a complete replacement.

    Be careful: don't forget to check the entire room to be sure you're not leaving other areas of wet moldy carpeting in place. - Thanks to reader Eva for these suggestions.
Photograph: Moldy carpeting - Daniel Friedman
  • Carpets over wet padding or carpets, carpet padding, or carpet tack strips which are water stained or moldy indicating that water or condensation has been present below the carpet. The photo shown here is an example of a moldy carpet tack strip which offers a clue of a limited area of water entry in a basement although no staining was visible on the exposed top of the carpet.

    Notice the small brown stain spots on the back side of this carpet? These are rust marks from the carpet tack strip - another indicator of wet conditions below this carpeting.
  • Carpets in basements or located on floors below grade such as in split level homes, particularly in areas where there are periods of high humidity or wide temperature swings in a building likely to produce condensation.
  • Carpets exposed to high pet traffic are likely to have a high level of animal dander and, depending on the building humidity history, almost always have a high level of mite fecals and other allergens - this is not a mold problem but is likely to be an IAQ problem especially for people who are asthmatic or allergic to pets.

    I have tested carpets before and after home vacuuming, home HEPA vacuuming, and professional dry and wet process cleaning. None of these methods can completely clean a carpet, though they might temporarily reduce the level of particles in the very top of the carpet nap.

Smelly carpet mildew (C) Daniel Friedman

  • Carpet mildew diagnosis: carpeting that has light mold or smells like mold might be described by an inexperienced inspector or a building owner as mildewed carpeting. It's moldy.

    Our photo of moldy carpet (left) was taken from a sample of carpeting that was the final target of a building mildew odor diagnosis procedure.
    see MILDEW ERRORS, IT's MOLD for details.
  • Carpet odors: carpeting that smells can be caused by a wide range of problems.
  • Carpet stains: can also be caused by a wide range of sources, some of which are harmless, others may diagnose other building problems such as a heating system that is not working properly, or building air leaks.

How to Look for Hidden mold in or underneath wall to wall carpeting and carpet padding

Advice for Testing Indoor Carpeting for Mold Contamination

If carpeting has been wet and was not dried within about 24 hours after that event, it is likely to be moldy. if carpeting smells or looks moldy it also will almost certainly need to be replaced. But what if we don't know a carpet's history, we don't see mold on the carpet nor on it's underside, but we need to test the carpeting for mold?

Details of our advice on testing carpeting for mold or other contaminants can be read at CARPET TEST PROCEDURE.

In addition to taking a careful case history of the leak exposure to which carpeting has been exposed, and in addition to making a thorough olfactory (subjective smell test) and visual (by eye) inspection, we on occasion test carpeting using a vacuum method, combining a vacuum pump with a sampling cassette.

Selection of the area of carpet to be tested is important: choose the most-suspect area of carpeting such as where leaks or water are likely to have been present or where there may have been cross-contamination from mold remediation in other areas of the building.

We advise against use of tape samples of a carpet upper surface to screen carpeting for mold since there is a significant risk that such methods will fail to detect problem mold that is in the carpet but not on its uppermost surface. This condition occurs, for example, when moldy carpeting has been HEPA vacuumed or cleaned.

However, if there is mold already visible on a carpet (such as is shown in the next section of this article) it may be appropriate to collect a surface sample using tape in order to identify the type of mold present when that data is needed for medical or post-remediation clearance test purposes.

How to Recognize Mold Visible on Exposed Carpeting Surfaces

Moldy carpet stains (C) Daniel Friedman

Mold visible on carpeting surfaces: As we also mentioned
at CARPET PADDING ASBESTOS, MOLD, ODORS, carpets or even area rugs may not actually be mold contaminated but can smell moldy if the carpeting or padding have absorbed Mold-related Volatile Organic Compounds
( MVOCs).

In the case of the moldy carpet photo at left, we suspected that the visible carpet mold was the "tip of an iceberg" of hidden mold below.

Details about types of stains on carpeting, their cause, significance, and cure, are at CARPET STAIN DIAGNOSIS.

Watch out: carpets can absorb other odors besides mold. And watch out for over-using ozone treatments that may oxidize building components and lead to a new and horrible chemical like smell.


Should I Test my Moldy Wall to Wall Carpeting?

Question: is a tape sample of my mold-suspect carpeting surface useful?

I took a clear tape sample of some mold on the carpet in my baby's bedroom, but I don't see any visible mold on the sample, even though I pressed fairly hard. Is that ok to send to you, or must I see the mold on the tape? I just don't want to waste anyone's time by sending an insufficient sample. S.P.

Reply: Testing a Moldy Carpet is Usually Not Needed

Thanks for asking. Our suggestions below, basically recommending that you do not have this carpet mold sample processed, are opinions based on ethics (don't peform unnecessary lab tests), and common sense, not out of a reluctance to be of service:

  • If the carpet is visibly moldy, smells moldy, got soaked, it almost certainly needs to be removed and disposed-of along with the padding. It is near impossible to completely clean mold from wall to wall carpeting, and trying to do so risks health issues as well as wasting money. Toss out moldy carpet, being careful not to spread moldy dust throughout the building in the process, and clean the exposed surfaces, and of course, fix the cause of mold.
  • A carpet surface tape sample, unless there was visible mold, is too unlikely to represent the actual mold-condition of the carpet. If we have a technical reason to actually determine what kinds of mold are present in carpeting, for example to allow a client to inform their doctor to what molds they've been exposed at high level, we use a vacuuming method that pulls particles from the carpet interior, under-side, top side, and carpet padding as well as checking the conditions of the subfloor below. Details are
  • And if there is mold visible on the carpet surface, our first point pertains. Despite claims to wash and restore carpets, that approach has not done well in the field and lab tests we've conducted.

Some exceptions to this no-carpet-test advice / opinion

  • If there was only very small moldy spot caused by a limited-scope, well understood event - such as a child left a piece of apple wet-side down on the carpet- that's such a localized problem that ordinary cleaning should suffice, and replacing the carpet ought not be necessary. That's because we know the cause, we know there was no extensive wetting nor mold growth, and we are not facing conditions that make further mold growth likely - at least not from the apple.
  • If occupants of the building where moldy carpeting is or has been installed need to inform their physician, pulmonologist, or allergist about the molds to which they have been exposed - in which case other building screening samples (such as settled dust) and a more thorough inspection may be in order, lest we focus on the "wrong mold" reservoir or miss something else important.
  • Carpeting that is not permanently installed can be removed and sent out for professional cleaning and drying and if appropriate, tested before it is reinstalled in the building.


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