Mold on dirt in crawl (C) Daniel Friedman Mold on Dirt in Crawl Spaces, Basements, Floors

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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.

Thanks to reader prodding we include five simple steps for dealing with mold growth on the dirt floor of a basement or crawl space.

Yellow mold in crawl spaces may be destructive Meruliporia fungus. White mold found on crawl space or basement dirt floor may be a basidiomycete. Photographs of mold growing on dirt crawl space floors - soil fungi under or in buildings. Indoor "mushrooms" growing in or on buildings.

Our photo (above) shows thick pale yellow fungal growth on dirt in a damp crawl area.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

MOLD on DIRT FLOORS: Mold on Dirt in Basements & Crawl Spaces

Photograph: fungus and mold growing on dirt at a crawl space concrete block wall - © Daniel FriedmanSignificance of Indoor Soil Fungi - "Dirt Mold" growing in building basements & crawl spaces

A broad range of fungal species among at least seven genera may be found growing on or in soil [1] 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] 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.

What to Do about Mold on Dirt Under a Building: 5 Steps

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. After the following summary we'll offer more-detailed suggestions for dealing with mold on the dirt floor of a crawl space or basement.

  1. REMOVE obvious heavy fungal or mold growth from the dirt surface
  2. INSPECT for and clean off or remove mold from other surfaces in the same area
  3. DRY OUT The dirt-floored area and stop the water or moisture sources
  4. INSTALL a 6-mil or heavier poly / plastic vapor barrier over the dirt surfaces
  5. CHECK for rot or insect damage in the area

Below we expand on those five steps for dealing with mold on dirt under buildings.

Step 1: Remove Mold Contamination From a Dirt-Floored Area

Meruliporia fungus on dirt in a crawl area (C) Daniel FriedmanFirst let's note that most soil fungi that are happy in wet soil are not likely to be airborne contaminants in the building above.

However the same conditions that produced those fungi that you see on the dirt surface may also produce more worrisome fungal genera/species that are easily airborne but sometimes harder to see, such as Aspergillus sp. or Penicillium sp. So it makes sense to clean up and dry out a wet dirt-floored crawl or basement area.

Photo: Meruliporia incrassata mold on dirt according to the reader who sent us this photo. [Click to enlarge any image]

"Cleanup" of moldy dirt means, at most, scraping or very shallow (1" is enough) digging; this will NOT stop mold growth but it'll remove the fruiting bodies and might slow the growth of further mold; Do not launch an expensive / extensive digging and soil removal project.

It's not likely to be needed nor helpful. You'd have a heck of a time removing all mold and even if you could, until you correct the conditions that caused the mold growth mold will return anyway - all mold genera/species are everywhere all the time - in air, looking for a nice place to land and grow.

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.

Should you test the mold on the dirt? Probably not.

You do not normally need to "test" the mold to identify it since that won't change the cleanup and prevention measures.

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.)

Really? Mold testing to identify the genera/species is not needed nor useful unless you need to know the identification of the specific molds present for medical reasons (ask your doctor) or to permit a later check against the possibility of cross-contamination from a large, costly mold remediation job.

The mold cleanup and prevention measures are the same regardless of the mold genera or species.

Step 2: Check for & Clean or Remove Other Mold Contamination or Other Mold Friendly Stored Items

Mold contamination of wood floor structure (C) Daniel FriedmanBesides looking at the mold on the dirt floor, be sure to also check wood framing, wood subflooring, any stored items such as boxes.

Note that insulation may be moldy even if it looks clean, particularly if the insulation has been exposed to a large area of mold growth on wood, paper, or other mold-friendly materials nearby.

Remember also to remove junk stored in the area that invites mold growth such as cardboard boxes, old furnishings, and that Barbie townhouse that was left by your kids back in 1982.

If fiberglass insulation has been exposed to high levels of airborne mold on wood surfaces it's probably best to remove it, clean the surfaces, and re-insulate once the area is dry and clean.

An example of using media blasting to clean wood surfaces in a hard-to-access area is at MOLD CLEANUP, WOOD FRAMING & PLYWOOD

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.
also USING LIGHT TO FIND MOLD - how to use light when looking for mold.

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.


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.

Remove Other Nutrients Encouraging Crawl Space Mold and Mold on Dirt

Mold on dirt (C) Daniel FriedmanMold might also be growing apparently on dirt but actually on something that spilled or was left atop the dirt - which could mean other fungal species than the soil fungi we just cited.

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 EFFLORESENCE & 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.

Step 3: Dry out the dirt-floored crawl space or basement area

Dehumidifier at work in a wet crawl area (C) Daniel FriedmanDry out the area. It's essential to also find and correct the cause of mold growth:

This includes fixing outside sources of water such as improper roof drainage and improper surface grading.

Also check that no plumbing drains or supply piping are leaking into the area.

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.

To speed dry out of a wet area we may use dehumidifiers connected to a condensate pump or draining to a sump pump by gravity so that the dehumidifier can be left running constantly.

We might make temporary use of fans to move air around to speed the dehumidification process.

Keep in mind that dehumidifying won't work if there is still water entry from anywhere.

Watch out: drying out mold, particularly Aspergillus sp. or Penicillium sp. on wood or paper surfaces can result in a temporary but enormous surge in the level of airborne mold.

So for large areas of mold contamination (more than 30 sq .ft.) the professional remediators whom you hire will doubtless also set up temporary negative-air machines (NAMs) to blow air out of the basement or crawl space so that mold spores don't get to enjoy irritating the building occupants on floors above.

See CRAWL SPACE DRY-OUT PROCEDURE for a good place to start fixing damp or wet crawl spaces

See WET BASEMENT PREVENTION for more help with drying out wet basements and preventing water entry

Step 4: Put Down Plastic over Dirt Floors

Sealed crawl space after a mold cleanup job (C) Daniel FriedmanInstall a 6-mil or heavier poly / plastic vapor barrier over the dirt surfaces and up walls about a foot; ideally you'd seal or affix the plastic to the walls.

Plastic will break the natural "moisture pump" that occurs when wet soil is below a building:

moisture evaporating into the air above the soil actually acts as a pump to draw more soil-moisture upwards: the dirt under the building, fed by an outdoor moisture source or by indoor leaks, continues to pump moisture into the structure.


Optionally, if you want extra moisture-proofing of the area you might consider, once it's been cleaned of mold, spraying a fungicidal sealant on the wood surfaces of the basement or crawl space ceiling and sill plates.

See FUNGICIDAL SPRAY & SEALANT USE GUIDE for more information.

Our photo shows a white moisture barrier over the soil of a crawl space where a significant mold reservoir has been removed from the wood surfaces above (the floor framing, supporting girder, and posts).

You'll note the shiny appearance of the wood. [Click to enlarge any image]

The mold remediation contractor who handled this job elected to seal the wood surfaces after the cleanup was complete. While the long-term life of fungicides that may be included in some sanitizers and sealants varies, the fact that the wood surface is sealed retards its moisture uptake so that in our OPINION that alone would help retard future mold growth.

Step 5: Check for Other Damage: Rot or Insects

Check for wood-rot or insect damage by a careful examination of wood framing and subfloors: wet crawl areas and basements invite both fungal and insect pests that can damage the structure.

The fungus in the moldy dirt floor photo above in this article was mailed to us by a client and was identified as Meruliporia incrassata - a mold that can attack wood structures causing significant damage.

We discuss this fungus at MERULIPORIA MOLD PHOTOS.

Although this recently-built home, located at 5500' in the Sierra Nevada mountains had crawl area ventilation, snow melt draining towards the structure caused chronic wet conditions and was surely a significant contributor to this mold growth.

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.

Indoor Fungi - "Mushrooms" Found at Building Foundations, Penetrations, Plastic Piping

Reader Question:

Indoor fungal growth at foundation & on PVC piping (C) InspectApedia Indoor fungal growth at foundation & on PVC piping (C) InspectApedia

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 picture 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

Reply: don't bother bleaching mold; remove it.

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 .

Reader follow-up:

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.

Mold fungi growing on dirt in a crawl space (C) InspectApedia GE Mold fungi growing on dirt in a crawl space (C) InspectApedia GE

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

Mold fungi growing on dirt in a crawl space (C) InspectApedia GE 


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.

Reader follow-up:

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.


Continue reading at CRAWLSPACE MOLD ADVICE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see MOLD APPEARANCE - WHAT MOLD LOOKS LIKE - details of what mold looks like on various building surfaces.





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MOLD on DIRT FLOORS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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