Mold growth on dirt & soil in, under, around buildings:
This article gives advice on how to find, identify, clean up or prevent mold growing on dirt or soil surfaces such as in building crawl spaces or in dirt floor basements. Our photo (above) shows thick pale yellow fungal growth on dirt in a damp crawl area.
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A broad range of fungal species among at least seven genera may be found growing on or in soil  and because the interaction between soil and seed fungi has been studied widely in work on plant pathogens, they are studied worldwide.
[Click to enlarge any image]
However, texts that help identify soil fungi may be incomplete when it comes to mold on or in or beneath buildings.
Building conditions that produce mold growth may generate fungi that vary from how they may appear in the lab in a culture plate, and building mold, even mold on dirt in a crawl space may appear different from the same genera/species growing in nature, say in the woods.
And because mycologists so often study fungi prepared from cultures, in my (DJF) experience, texts used as identification guides may present photographs of fungi that do not necessarily match what these same genera and species may look like when found in nature.
Here we provide photographs of fungi (mold) growing on soil in or beneath buildings. This article does not address the much larger topic of the genera of soil fungi. For that topic see Tsuneo Watanabe, Pictorial Atlas of Soil and Seed Fungi, Morphologies of Cultured Fungi and Key to Species, [at Amazon.com] Second Ed., CRC Press 2002, ISBN 0-8493-1118-7. [Disclosure: Amazon pays us a pathetic pittance on the sale of books listed here].
What is the Significance of Soil Fungi In a Building?
Our photo (left) shows a fungal fruiting body or mushroom growing out of a concrete block basement foundation wall. The yellow fungus growing on the mushroom may be a second opportunistic parasite.
Depending on genera/species a mold growing on dirt might be toxic, pathogenic, or allergenic, though in our experience (warning, we are not a mycologist).
Interestingly Watanabe reports that some of the mold genera commonly found as problematic mold reservoirs inside buildings or on building surfaces also include species found in soil, including two Stachybotrys species, S. corda and S. elegans, and a still longer list of Aspergillus species: including Aspergillus brevipes, Aspergillus fumigatus, Aspergillus niger, Aspergillus parasiticus, and others.
The growth of fungi on or in "dirt" below a building, say in a wet crawl space, should come as no surprise: soils both under buildings and in more natural settings (the woods) contain organic matter that contains nutrients inviting to molds.
Previously I had stated here that the chance that mold from crawl space dirt passes throughout a building as problem spores is lower than otherwise, principally because of the wet conditions in crawl spaces, but on learning that some easily airborne genera such as Aspergillus may be present, I have amended that position.
Mold on Crawl Space Dirt? Look Up!
More significantly, the conditions of moisture and presence of organic matter such as wood framing and also hospitable moisture holding materials such as fiberglass insulation all mean that where you see mold on dirt in a crawl space you should be looking "up" to inspect the building walls and floor structure overhead for other mold growth that could be a problem.
An inspection of wood framing and subfloor over a damp moldy
dirt-crawl space or basement should be conducted using light and careful examination of the surfaces.
In any event, ne would want to be careful not to get mold in a cut, or in your eye, even if it does not appear to be an airborne species that can be easily inhaled.
Other Nutrients Encouraging Crawl Space Mold and Mold on Dirt
In any case if there is only a small amount of mold - a few square feet - it's reasonable for a homeowner to remove the visible mold and surface soil - just an inch or less. There may be fungal components deeper in the soil, but we're going to address that by drying out the area rather than digging up the whole house.
Our photo (left) of white-colored mold on dirt , was contributed by a client whose crawl space contained Meruliporia sp. fungus on the dirt (see below).
We did not process a sample to identify this white fungus in the lab. It may be a different species from others in the crawl area, and its growth may have been related to items such as cardboard or wood left on the dirt floor, or due to a buried concrete block - notice the roughly rectangular pattern of the white mold growth at the center-right in the photo.
But before sampling what looks like "white mold" on dirt or on a masonry surface, take a look at Efflorescence & white or brown deposits - very often the white crystalline looking substance in these locations is not itself mold, though it is a moisture indicator, meaning mold may be nearby.
What to Do about Mold on Dirt Under a Building
Many readers have asked us what to do about mold found growing on crawl space dirt or on a dirt basement floor. I've often seen orange and yellow molds and yeasts growing on wet dirt in these areas.
If the area of mold on dirt is large, more than 30 sq. ft., and if it's not a harmless cosmetic mold, professional cleanup would be appropriate, but only after a competent and independent (independent from the cleaning company) inspection diagnosed the extent and cause of mold and thus provided you with a mold cleanup plan.
If you see a large area of moldy soil that appears homogenous in character (color, pattern, growth surface, etc) then it may be economical to collect a sample to send to an independent lab for identification (mine or any independent mold testing lab - we give instructions on how to collect mold samples at Mold Test Kit Procedures.)
It's essential to also find and correct the cause of mold growth: Any mold cleanup anywhere in a building, whether its on crawlspace dirt or basement soils, must be followed by a diagnosis and correction of the moisture source that invited the mold growth, or the mold problem will simply recur.
The fungus in this photo mailed to us by a client was identified as Meruliporia incrassata - a mold that can attack wood structures causing significant damage.
We discuss this fungus
Furthermore, and possibly more important, soil mold in a basement or crawl space is an indicator of wet conditions, which means that more-problematic molds may be growing on wood or paper or other organic surfaces nearby - and may be more of a problem for building occupants.
For example if insulation were installed in this crawl space ceiling it would be likely to have mold contamination, though more likely from Aspergillus sp. or Penicillium sp. - different fungal genera/species prefer to grow on different materials.
MOLD in BUILDINGS 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. (See TEST KITS for DUST, MOLD, PARTICLE TESTS for details). 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.
Indoor Fungi - "Mushrooms" Found at Building Foundations, Penetrations, Plastic Piping
This growth was discovered last week on my hot water heater pvc pipe. It has contact with water it looks like because the water heater has a slow leak that maintenance never fixed. The water is about half way up in the pan that the heater sits in. My maintenance man was going to spray it with bleach and remove it but I am terrified of what it is and if it's harmful!
My central A/C and heater sit directly above the water heater in a small closet. I insisted that they have someone come out and test a sample of it. They had a company come out but they have not told me any results. The guy did tell me when he was here that he's never seen anything like it.
He said he's seen similar looking fungus but never in an indoor environment and especially on PVC to a hot water heater. The results will go to my apartment manager so I am dependent on them to tell me. Can anyone tell me what this could be? I'm am very worried about this.
My last email would only allow one pic due to it's size so I am sending another pic in this email to show the front side of this unusual fungus growth on my water heater PVC. I have looked everywhere and cannot find anything online that comes close to resembling this. - R.S. Madison TN, 3/30/2014 /P>
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. For example I pose some additional investigative questions below. And you will find additional depth and detail in articles at our website. That said I offer these comments:
A mycologist might recognize your indoor mushrooms, but I can't positively identify your fungus from the photographs. The chief fungal growth certainly looks like coral fungus or a coral slime fungus. Depending on the genera/species, e.g. Ramaria formosa or Ramaria gelatinosa, these are poisonous - that is, not edible. Your first photo at above left also sports an upside-down (dying) basidiomycete-like black gilled mushroom. More indoor mushroom growth examples are shown and discussed
at our more lengthy catalog of fungi, mold & mushrooms growing on building contents & materials:
In any event there is certainly no reason to panic. The total quantity of fungal material in your photos, if that's all there is in the building, is trivial. Typical standards calling for professional mold cleanup involve areas of 30 sq. ft. of continuous moldy surfaces or more.
Furthermore, "bleaching" fungus is an incorrect approach to the problem and IF there is mold growth in your building that might release irritating or harmful airborne spores or MVOCs the correct approach would be to remove the fungus -clean it off - and correct the cause for its growth.
What makes sense to me would be a more thoughtful inspection for the leaks and water entry that encouraged this fungus to grow in the first place. "Bleaching it" without correcting the cause for growth would be pointless and risks leaving a larger but more hidden problem in the building .
Tank you for your very prompt and informative reply! I totally agree that the underlying cause of this is crucial. If this is the coral type of fungus, which I know you can't guarantee from a pic, would drinking my tap water and brushing my teeth expose me to ingestion of the toxins? I know that may be a stupid question but my lack of knowledge on these things has my paranoia at extremes since seeing this thing!
My maintenance guys were supposed to replace the hot water heater back in November of last year due to the possible slow leak but have never addressed it. It took me almost a year to get my porch door replaced that was rotting all inside the frame. That was done last week by a contractor that my apartments hired. While he was here I asked him to look at my water heater and he is the one that noticed the growth! I would have never noticed it because it looked like expanding foam from a distance and the mushroom is growing from the backside that I can't see. I snapped a pic of the back with my phone camera and that's when I saw the mushroom!
I will most definitely let you know what the outcome is on this! When will you be putting up my pics in your article? Will having me as the contributor better able me to receive responses to possible underlying causes? If so, then yes please do so.
I guess the only "stupid" question is the one not asked.
But I cannot imagine how a fungus growing in soil or on a foundation wall or even touching the outside of a PVC plumbing pipe would introduce toxins into the water supply. Now IF a fungus had invaded a pipe interior that might be a different matter but, then, you'd surely also see if invaded from the outside such a pipe would also be leaky.
Are we sure we're looking at a PVC water supply pipe? - from the scale of the photo I was not sure this wasn't a drain line.
Reader Question about Mold in Dirt Crawl Space
Hi I have attached a few pics of the mold growth on my dirt crawl space each pic is isolated and no further spread is seen anywhere else. I was actually shocked to see this strange looking growth. I do keep the crawl vents open but there is no forced air movement at all. Please assist as to how to safely remove.
The house sustained a fire in may of 2014 and the ac system has been off since. There are fans running in house though. The only power to crawl space is to the sump pumps that discharge any water to the outside via pipes which none of the pics of the mold spores / mushrooms are even close to the sump liners of perimeter pipe in perimeter ditch.
There is no black plastic liner on dirt floor and no floor joist insulation, I removed all several years back when I dug my perimeter ditch and sump pits with the plastic liners. Thanks for any guidance! - G.E. 9/8/2014
What lovely crawl space mold photographs. And your blue fungus one I've not seen before in buildings.
Most likely these grow where you see them because of a combination of moisture and organic material spilled on or in the soil.
Your note describes a damp or wet crawl area and one that was probably severely soaked - even flooded when the building fire occurred. These conditions invite mold growth, but it's ongoing moisture that keeps it going and looking so fresh as in your photos.
You can dig out (just an inch or so) the visible mold, toss it into the woods or into garbage, then put down plastic, and take other steps to dry out the area.
Probably more important than the mushrooms found growing in this dirt crawl area would be mold growth on the exposed wood framing or in insulation if there is some in the crawl area.
For that topic
see INSULATION MOLD TEST
For more about mold contamination in fiberglass insulation, (if there is insulation in your crawl area) see FIBERGLASS INSULATION MOLD
Watch out: the growth of these fungi on dirt blow a home mean that wet conditions continue to the present: the growth you show in your photos is fresh and lively - so I would not blame it solely on the fire previously suffered by the home. You will want to find and fix the sources of water entry, high moisture, or leaks into the crawl area and you'll want to inspect enough to know if there is mold removal or cleaning needed on the crawl space surfaces: not just the dirt floor but wood framing and wood subfloor overhead.
See CRAWL SPACE DRYOUT - live link just below - for procedures to prevent further mold problems in the crawl area.
9/8/2014 Do you have any contact to send the pics to that could possibly identify the type fungi? Could you please remove fire date from email and also email address as you stated and as well my name before posting. I will keep you apprised of progress. I read that after I dig up the fungi and discard to pour straight vinegar in area. Have you heard this approach? - G.E.
The large mushroom like fungus is a basidiomycete. The blue fungus is uncertain.
Photo identification from just the fruiting body is possible for the blue fungus - look in any mushroom guide book in your local bookstore.
But I was not clear enough in my prior email. The health risk from the fungi in your photos, in the quantities and location shown, is virtually nil unless you eat one of these or rub it in your eye.
The more serious risk would be mold growth over a large area of wood framing or subfloor - which won't look like mushrooms.
See MOLD APPEARANCE - WHAT MOLD LOOKS LIKE for details of what mold looks like on various building surfaces.
Continue reading at CRAWLSPACE MOLD ADVICE or select a topic from the More Reading links shown below.
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