How to Inspect, Diagnose, & Repair Problems in Building Crawl Spaces
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This building crawl space article series explains how to inspect, diagnose problems in, and repair building crawl spaces, including crawl space insulation & leaks or moisture control. Information is provided about visual clues of crawl space problems, such as
evidence of a history of leaks, mold contamination, insect damage, structural damage, flooding, as well as evidence of hazardous materials and conditions such as the probable presence of animal allergens, asbestos, or mold.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Crawl Areas: Defect Recognition, Repair, Prevention for Building Crawl Space Leaks, Mold, Insulation & Ventilation
Thepage top sketch of the role of a dirt floor crawl space in building moisture and mold problems (above) is courtesy of Carson Dunlop Associates. Photo at left is of the author, Daniel Friedman, peering into an inaccessible crawl space while suffering from a broken leg. Photo courtesy of Arlene Puentes.
The list of concerns or problems in or due to building crawl spaces is long as would be a list of opinions about what to do with crawl spaces, wet crawl spaces, moldy crawl spaces, or crawl space insulation and ventilation. Good building science combined with a lot of experience has led to some good information on how to correct crawl space problems. Here we list crawl space problem inspection, diagnosis, and cure. Here are some things to watch out for in a building crawl space:
- Crawl spaces may be unsafe to enter due to risk of asbestos, chemicals, collapse, hantavirus, mold, rodents, sewage, snakes or even electrical shock hazards. See CRAWL SPACE SAFETY ADVICE where we explain when you should not even enter a crawl space. Also see CRAWLSPACE MOLD ADVICE. Do not enter such an area without protective gear and appropriate training.
- Crawl spaces may be a source of building water, moisture, leaks, mold - see CRAWL SPACE DRYOUT PROCEDURES - this is the key article on dealing with wet or damp crawl spaces and related problems in buildings. Also see CRAWL SPACE GROUND COVERS. For avoiding foundation collapse in areas prone to flooding, also see FLOOD VENTS & FLOOD PORTS. WATER ENTRY in BUILDINGS is the home page for our series of articles on the causes and cures of high indoor moisture, wet basements, wet crawl spaces, and moisture related problems like attic condensation and mold. Also see Mold in Fiberglass Insulation.
- Crawl spaces may be a cause of building energy loss or increased heating bills, especially if the crawl space is improperly insulated and/or vented. See CRAWL SPACE DRYOUT PROCEDURES where we also discuss the change in thinking between the old-school idea of venting crawl spaces to the current best practice of converting crawl areas to a conditioned space, explained further at CRAWL SPACE GROUND COVERS.
- Crawl spaces are often a reservoir of hidden structural, rot, insect, mold, water, contaminant, or other problems, largely because most crawl areas are difficult to enter and are rarely inspected. Rot, fungus, termites, carpenter ants, powder post beetles, & other wood destroying organisms are a special risk in crawl areas, especially if fiberglass insulation was run from crawl space floor right up the wall and onto building framing or flooring.
- Crawl spaces may be cluttered with debris impeding inspection and inviting pests or rodents. Crawl spaces are required to be kept clear of debris; some such as wood scraps increase the risk of termite risk. For example from the 2012 IRC:
The under-floor grade shall be cleaned of all vegetation and organic material. All wood forms used for placing concrete shall be removed before a building is occupied or used for any purpose. All construction materials shall be removed before a building is occupied or used for any purpose. [1]
Key Crawl Space Inspection, Diagnosis, Repair articles
AIR BYPASS LEAKS - stains on insulation may help spot air leaks from a crawl area into the occupied space
BASEMENT LEAKS, INSPECT FOR - these water and leak control articles also apply to crawl spaces
BASEMENT WATERPROOFING - these water and leak control articles also apply to crawl spaces
BUCKLED FOUNDATIONS due to INSULATION? - does foundation insulation cause cracking visible in a basement or crawl space?
COMBUSTION AIR for TIGHT BUILDINGS - if you have heating equipment in a crawl space be sure there is adequate combustion air in and venting of exhaust gases out

CRAWL SPACES - home page for building crawl area topics
CRAWL SPACE DRYOUT PROCEDURES - this is the key article on dealing with wet or damp crawl spaces and related problems in buildings
CRAWL SPACE GROUND COVERS
CRAWL SPACE INSULATION RETROFIT
CRAWL SPACE SAFETY ADVICE
CRAWL SPACE VAPOR BARRIER
CRAWLSPACE MOLD ADVICE
MOLD CLEANUP by MEDIA BLASTING
MOLD ON DIRT FLOORS
DEW POINT CALCULATION for WALLS - why does condensation appear on a crawl space wall or on the ceiling above it ?
DEW POINT TABLE - CONDENSATION POINT GUIDE
EFFLORESCENCE, Salts & White / Brown Deposits - don't waste money testing white goop for crawl space mold if it is efflorescence, but efflorescence does indicate a source of crawl space moisture that needs attention

FIBERGLASS INSULATION - can become mold contaminated in a crawl area, leading to mold contamination in the occupied space above
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP - careful inspection of the crawl area is important
FOUNDATION WATERPROOFING - for crawl areas
INSULATION LOCATION for CAPES, CRAWLSPACES - what insulation works best in crawl spaces? where should crawl space insulation be placed?
MOISTURE CONTROL in BUILDINGS - key advice for drying out a wet crawl area
Key Crawl Space Water Entry Diagnosis and Cure Articles
List of additional building crawl space inspection and defect articles
Animal odors in buildings - how to find and remove animal odors, pet urine odors, etc. - Is there a dead skunk in the crawl space below your home?
- ASBESTOS IDENTIFICATION IN BUILDINGS - are there asbestos hazards in the crawl space?
- BASEMENT WATERPROOFING and FOUNDATION WATERPROOFING collect articles on keeping water and moisture out of buildings
- Fiberglass Building insulation: are fiberglass particles a problem in the crawl space? Has the crawl space insulation become a mold reservoir?
- FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP A Guide to Mold Cleanup Procedures
- HEAT LOSS in BUILDINGS, how to determine and calculate heat loss from a building crawl space (or heat gain in a cooling climate), how to evaluate building insulation, & how to insulate buildings
- Humidity: How Low Should You Keep the crawl space humidity to avoid a mold problem
- INSULATION INSPECTION & IMPROVEMENT: Insulation in crawl spaces: Identification, R-values, Heat loss, Insulation Types, Insulation Characteristics
- Mold Cleanup, How to clean or remove mold in crawl spaces
- Mold Prevention: Avoiding Mold Problems in crawl spaces by Using Mold-resistant Construction Products & Practices
- Mold Information Center: What to do about crawlspace mold, mold action plan, valid and invalid test methods, mold remediation
- ODORS & SMELLS DIAGNOSIS & CURE - how to identify and remove all kinds of odors in crawl spaces
- Rot, fungus, termites, carpenter ants, powder post beetles, & other wood destroying organisms are a special risk in crawl areas
Thermal Tracking & Stains how to recognize thermal tracking or thermal bridging & how to diagnose Stains on Ceilings & Walls, Building Air Leaks & Insulation Defects, as well as other indoor air quality or building concerns
- SUMP PUMPS GUIDE - does your crawl space need a sump pump?
- WATER ENTRY in BUILDINGS series of articles on the causes and cures of high indoor moisture, wet basements, wet crawl spaces, and moisture related problems like attic condensation and mold.
- WINTERIZE A BUILDING - how to protect a building and its plumbing and mechanical systems from freeze damage, how to shut down a building to minimize damage; how to de-winterize a building.
Frequently Asked Questions (FAQs) about wet or damp crawl spaces, crawl space mold, crawl space hazards
Question: What is the Best Approach to Drying out a Flooding Crawl Space?
I have been battling crawl-space moisture and puddling problems for about 2 years now and am desperately requesting your pro-bono assistance and consultations. I am living in a senior citizen retirement house that I inherited from my deceased parents. I am on total permanent Social Security Disability for almost 10 years now. This is my only income which is $1300 per month.
After many many hours, weeks, and months of calling people, searching the internet etc., I came across your excellent article and web-site. I knew from reading your material that you are the people I need to help me navigate properly through all the people and companies I have been in contact with. I didn't, (and still don't) know where to start first.
This house was built in a senior citizen community where the water-table is high and the ground gets soaked around the perimeter of the foundation and other areas of the property during heavy and even not-so-heavy rains. I have a dirt crawl-space that gets puddles in it and had a termite inspector put a not-so-good sump pump in it that the water never reaches.
Then another person told me I had mold in there and several other people told me I didn't. Had an excavator look and he told me the dirt needed to be pitched and leveled but he's never done that in a crawl space before. Even when the termite guy dug some trenches, the water just sat in the trenches.
I had water-proofing companies come and tell me differing things, all wanting thousands of dollars and none guaranteeing anything. Some say encapsulation and inside french drains, some say that's not good and outside french drains, some say putting more wall wells and vents in or digging the dirt out more so that water won't come in the vents. I consulted with a hydro science company that also said to just clean the gutters (which I already had done and they have that netting over them so they weren't too bad) and clean or get new downspouts. And it goes on and on and on.
I want to get the right people to start at the right place but am thoroughly confused now. I got free weatherization from the state because I am on limited income and on medicare, paad, and food stamps. They wrapped the pipes down there and put in a cheap black moisture barrier and fiberglass insulation on top.
I have heard and read that may make the moisture and mold problems worse. Recently I have noticed a mildewy moldy smell coming from my forced-air gas baseboard registers and read when I put the heat on it will spread and contaminate the house even more with mold spores.
I know my carpeting needs to be removed and house painted but have been putting if off because I realize I need to get the water/moisture issues identified first as well as the mold problems corrected. I had the bathroom painted in April and shortly after I noticed the paint cracked on the ceiling which is near the attic where I suspect there may be water/mold damage.
This, I think is probably from a couple of years ago when my central air was dripping and we had a new a/c put in.
So I am asking you for your help in testing for molds and dust particle analysis as well as directing me to the correct professionals in the proper order to resolve all these issues.
Thank you very much for your kind consideration and assistance in advance,
- B.B., Toms River NJ
Reply: A Step by Step Approach to Wet Crawl Spaces
Thank you for the interesting or I should say challenging water entry question - it helps us realize where we need to work on making our text more clear or more complete.
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem.
That said, here are some things to consider,interspersed with your remarks from your own note:
I have a dirt crawl-space that gets puddles in it and had a termite inspector put a not-so-good sump pump in it that the water never reaches.
Puddles in a dirt crawl space below a home, even just wet soils, invite problems with building mold contamination and wood destroying insects such as termites and carpenter ants. It's certainly a problem that needs correction. Divide your wet crawl space solution thinking into these three main topics:
- how to stop water from entering the crawl area
- how to get rid of water and moisture therein
- how to evaluate the building for related damage (mold, termites) that may need attention
Then another person told me I had mold in there and several other people told me I didn't.
If mold is not visible and there are no health complaints there might not be a big mold problem, or there may be one but as mold does not affect everyone to the same degree, you may not have noticed it.
See our article on MOLD EXPERT, WHEN TO HIRE, for help in deciding if it is cost justified or otherwise appropriate to perform some expert inspecting and testing for mold. Don't rely on mold tests without an inspection by an expert.
If your expert finds that there is a significant mold problem originating in the crawl area, also see CRAWLSPACE MOLD ADVICE.
Had an excavator look and he told me the dirt needed to be pitched and leveled but he's never done that in a crawl space before.
I agree with your excavator - if the crawl space is not sloped to a common drain point you cannot easily remove water therein. It's best not to have water enter the crawl in the first place since if we let water enter but then pump it out, we are still facing mold and insect troubles stemming from high moisture in the area.
Even when the termite guy dug some trenches, the water just sat in the trenches.
This means that the soil has a slow percolation rate. Trenches need to be pitched to a common drain point where a sump pump removes water.
I had water-proofing companies come and tell me differing things, all wanting thousands of dollars and none guaranteeing anything.
Beginning with our article titled CRAWL SPACES and also CRAWL SPACE DRYOUT PROCEDURES you will see an organized approach to curing a wet crawl space.
The number one water entry step is gutter and leader maintenance.
You think your gutters are "clean" but a mere handful of leaves can clog a downspout and lead to gutter overflow and spillage around the building so you will want to inspect the gutter and downspout system during a heavy rainfall. Make sure downspouts drain far enough from the building that water does not enter at those locations.
Some say encapsulation and inside french drains, some say that's not good and outside french drains, some say putting more wall wells and vents in or digging the dirt out more so that water won't come in the vents.
Simpler and less expensive are steps to stop water entry from outside, combined with a sloped crawl surface to a common sump pit (see SUMP PUMPS), combined with 6 mil poly over the dirt to stop pumping soil moisture into the area (see CRAWL SPACE VAPOR BARRIER).
I consulted with a hydro science company that also said to just clean the gutters (which I already had done and they have that netting over them so they weren't too bad) and clean or get new downspouts.
Your hydro science company was pointing to the number one cause of wet crawl spaces
Question: Problems with odors from poly vapor barriers on crawl space floors
I have a dirt crawl space under my bedroom floor which is causing me some health problems. I am extremely allergic to mold and my husband put 6 ply visqueen on dirt floor & 2 vents in block. I became extremely sick from visqueen order and I removed it, still feeling sick but not as bad. I am closing off the 2 vents to avoid anymore air flow in crawl space.
However, I want to put something down overtop the dirt floor and adhere it to the concrete walls to avoid any further allergy problems plus have cleaner air flow in our bedroom....but the plastic's are mostly made of polyurethane which might be sensitive too also or with the combinations and exposure to the dirt floor caused more airborne mold spores & allergies.
Even in the middle of the night I feel like something is crawling & biting me....and my husband is coughing something awful and we both have headaches & sinus, breathing problems too, nausea, disoriented and confusion. I am very worried about this and want it repaired ASAP before its too late. I am looking for something to cover & seal the dirt flooring but want something that is chemical free. I would also like to know if it would be wise to put insulation up underneath the bedroom floor to help prevent from coming up thru the floor into the bedroom? Any information, suggestions, ideas would be greatly appreciated. thank you! - Suzanne
Reply:
Suzanne, When choosing a poly vapor barrier for a crawl space beneath your home, indeed it makes sense to do a sniff test - some of the white 6-mil plastic vapor barriers I've seen used by building remediators were virtually odorless;
In other cases we placed the poly outdoors in the sun for a few days to help it complete its outgassing before putting it down in a crawl area. Indeed I've been bothered by horrible odor outgassing from some poly ground covers too.
You could also pour a concrete floor in the crawl area - a more costly solution that has its own concerns with temporary high moisture levels. More suggestions are at CRAWL SPACE GROUND COVERS where we describe ways to cover up dirt and stop moisture movement into the structure from the crawl space floor. Also see VAPOR BARRIERS & CONDENSATION in BUILDINGS.
But I wouldn't be too hasty to assume that plastic odors are the only concern, perhaps not even the main one, in your home. A damp dirt floor crawl space could have led to a mold problem or there could be other health and IAQ issues coming from that location or even elsewhere in the building. For example there could be hard-to-see mold contamination on wood surfaces or in fiberglass insulation if it has been exposed to wet or dampness. (See INSULATION MOLD).
At MOLD INFORMATION CENTER (article link at Related Topics ) you can find MOLD EXPERT, WHEN TO HIRE - that might help you decide if it's appropriate to bring in an expert for a more thorough building inspection and perhaps some tests. I'd be reluctant to ONLY blame the plastic odors (though those have bothered me too at times).
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- [1] International Residential Code, IRC Section R408, Under Floor Space, http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_4_sec008.htm, retrieved 3/2/2013
- [2] International Residential Code, IRC Section R406, Foundation Waterproofing and Dampproofing, http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_4_sec006.htm, retrieved 3/2/2013
- [3] Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees (Bylaws, Standards), as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Asbestos: How to find and recognize asbestos in Buildings - visual inspection methods, list of common asbestos-containing materials
- Asbestos Identification and Testing References
- Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.
- Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
- Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
- Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
- How could homes be designed and built more efficiently?
- What kinds of construction and production techniques worked well and which did not?
- How did people use different kinds of spaces in their homes?
- What roles did community planning, zoning, and interior design play in how neighborhoods worked
- "Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
- "Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
- "Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
- "Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
- Fiberglass: Indoor Air Quality Investigations: Health Concerns About Airborne Fiberglass: Fiberglass in Indoor Air from HVAC ducts, and Building Insulation
- Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
- Lighting, proper use of: proper aiming of a good flashlight can disclose hard to see but toxic light or white mold colonies on walls.
- Nogging: See this photo of exposed bricks on a building exterior on a building exterior in Canada. [Thanks to Carson Dunlop, Toronto - see References below].
- Rubblestone Wall Filler: See this Lartigue House using exterior-exposed rubblestone filler between vertical timbers of a post and beam-framed Canadian building.
- Slips, Trips, Missteps and Their Consequences, Second Edition, Gary M. Bakken, H. Harvey Cohen,A. S. Hyde, Jon R. Abele, ISBN-13: 978-1-933264-01-1 or
ISBN 10: 1-933264-01-2,
available from the publisher, Lawyers ^ Judges Publishing Company,Inc., www.lawyersandjudges.com sales@lawyersandjudges.com and also from the InspectAPedia Bookstore (Amazon.com)
- What Mold and Allergens Look Like: mold identification photos to help identify mold - choosing what to sample in buildings
- Manufactured & Modular Homes: Modular Building Systems Association, MBSA, modularhousing.com, is a trade association promoting and providing links to contact modular builders in North America. Also see the Manufactured Home Owners Association, MHOAA, at www.mhoaa.us. The Manufactured Home Owners Association of America is a National Organization dedicated to the protection of the rights of all people living in Manufactured Housing in the United States.
- Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens.
- How to Find and Test For Mold in Buildings A "how to" photo and text primer on finding and choosing the right spots to test for mold in buildings
- 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.
- Simple Adhesive Tape Sampling of Moldy Surfaces - how to send a mold sample to our lab
- ...