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This document gives advice on how to find and deal with mold growing on dirt or soil surfaces such as in building crawl spaces or in dirt floor basements. This is a chapter of "How to Look for Mold" 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.

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

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.

Depending on genera/species a mold growing on dirt might be toxic, pathogenic, or allergenic, though in our experience (warning, I am not a mycologist) I haven't come across dirt-growing molds that were species that were airborne - at least not at the time of our inspection and under wet conditions.

So the chance that such a mold passes throughout a building as problem spores is lower than otherwise. Still, one 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 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 I 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.

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 - I 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.

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.

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 - see our online article about how to use light when looking for mold.

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More Information on Building Diagnostic Inspections and Repairs

Mold and Allergen Recognition and Identification - Not All "Black Mold" is Harmful; Some Suspect Stuff is Not Mold

• 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
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• 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
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• 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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The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

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