How to recognize harmless black or dark colored indoor mold.
When investigating a building for a mold problem, you can save mold test costs by learning how to recognize Harmless Black Mold but which is often mistaken by some un-trained or inexperienced "mold inspectors" or "mold remediators" as more serious contamination which they call "toxic black mold".
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Some black mold in buildings arrived on the framing lumber and is harmless both to humans and to the building materials on which it is found. Often a visual inspection for certain clues (discussed below) can make you very confident of when mold appeared on lumber and what sort it probably is.
[Click to enlarge any image]
Because some clients have on occasion sent samples to our lab that really should not have been collected, much less looked-at, we provide this library of photographs harmless indoor mold and of things that are "not mold" and don't need to be tested.
In many cases these are substances that you can easily learn to recognize in buildings by simple visual inspection of the mold and its abutting and surrounding surfaces.
Save your mold test money, and increase the accuracy of your mold contamination inspection or test for toxic or allergenic mold in buildings: review these items to learn recognize non-fungal materials or even possibly harmless cosmetic "black mold" often mistaken for "toxic fungal growth."
Definition & Images of Sapstain Wood Fungi
"Sapstain" fungi are molds that grow principally on or in sapwood. There are three groups of sap-stain molds commonly discussed in the literature. Some literature also refers to "bluestain" fungi that is just about the same grouping. What are sapwood and heartwood anyway? Sapwood forms the main portion of a tree while heartwood is found only at the center of the tree. Most building framing lumber is almost entirely sapwood.
Dematiaceous molds (this just means molds whose spores appear dark or "black") including the two most common mold genera on earth, Cladosporium sp. (the "king of molds"), and Alternaria sp. (A runner-up for mold king based on frequency of occurrence).
Black yeasts, a sub-group of the mold family that include two very common molds Aureobasidium sp. (often found in moist attics on plywood as well as on wood framing), and Rhinocladiella (less often found in buildings).
Our photo at left shows a closeup of Aureobasidium sp. under the microscope. More mold microphotos can be seen
and photographs of common molds found in buildings can be seen
Ophistomoid fungi, a group that includes Ceratocystis sp. and Ophistoma sp., and related fungi - these are the most common cosmetic black molds found on framing lumber and sometimes on plywood, and are the main subject of this article - see our page top photo as well as more photographs below.
Because it is difficult in the lab to distinguish between Ceratocystis sp. and Ophistoma sp. by microscopic examination, and because these are not problem molds, most labs combine and report these fungi in lab samples as either Ophistomoid fungi, or as Ceratocystis/Ophistoma group fungi.
Watch out: building materials with cosmetic mold on them can also support growth of other problem mold species if later conditions are right for new mold growth. Many of our lumberyard samples of mold on wood examined in our own study of this phenomenon, especially samples collected from (wet) pressure-treated lumber contained both harmless cosmetic molds and an overgrowth of potentially harmful molds including mostly Penicillium sp. and some Aspergillus sp.
So inspect "cosmetic" mold growth areas carefully using good lighting techniques - see FLASHLIGHT HELPS FIND MOLD for details. Make sure that the obvious harmless "black mold" you see (such as shown in the photograph at left) is the only mold growth found.
As we describe later in this article at What to do about Cosmetic Molds on Indoor Building Surfaces, while most cosmetic mold can simply be left alone, we suggest that you do not assume that just because wood is obviously stained with cosmetic mold, that no harmful molds are present, particularly where damp, wet, or treated lumber is involved. Other fungi may also be present, so a closer look might be appropriate.
But if the mold growth is interrupted, it almost certainly was on the lumber at time of construction and is unlikely to represent an active building mold problem. That does not mean there could not be some other indoor mold problem, but if your mold looks like the photo on the rafter in the left of the photo just below, you are not looking at active building mold growth.
Interrupted Mold Growth Confirms No Active Mold Growth on Indoor Framing Lumber
Cosmetic molds [photo] such as the Ceratocystis sp./Ophistoma sp. group of Ascomycetes are not likely to be harmful to people nor to the wood they're found on. In these photographs of black mold on building framing you can see that the black mold "stops suddenly" at the photo at left or here at the cut end of a rafter [photo] and where a rafter meets the roof sheathing [photo].
Incidentally, that light brown material on the rafter in the upper right of our photo (left) is mud from construction, not mold.
While there are technical exceptions (such as mold growth interruption on drywall at a drywall taping joint), in general, indoor surface growing mold does not stop at an arbitrary "straight line" cut in or on a building material. (You can see this interrupted mold pattern growth on drywall
Other dark growths that may look "black" on wood surfaces include black yeasts such as Aureobasidium, often A. pullulans, as well as some of the most common species of Cladosporium sp.and Alternaria sp., some of the more common dark molds that we find on plywood roof decking in attics and on occasion on rafters. You can see photographs of these other dark post-construction attic molds
But the dominant "black mold" found on framing lumber at the lumber yard and in new construction, as well as remaining in homes after construction have been completed are the ophistomoids Ceratocystis and Ophistoma, whereas Aureobasidium sp. and Cladosporium sp. are more likely to have developed on a building surface after construction.
"Pressure Treated lumber" which is sold as resistant to rot and resistant to wood destroying insects is very often not only wet when purchased, but is often mold contaminated with several species of Penicillium sp. or Aspergillus sp.
We confirmed this condition by a survey of building materials at several lumber suppliers in New York, using tape samples of visible mold on the surfaces of these products as well as by testing framing lumber found at active building sites (photo at left and others on this page).
Various sources have reported that Ophiostoma grows in culture on media that contains cycloheximides, an agricultural fungicide that inhibits protein synthesis, so it is plausible to pose that it may have grown on wet treated lumber after the wood was processed with fungicides intended to prevent insect attack. It's ironic that treatment to prevent termite or carpenter attack on framing lumber appears to actually increase the growth of these molds on the same product.
We also found that sometimes "green" pressure-treated lumber, often Southern yellow pine (SYP), contained both cosmetic black molds (described above) and additional Penicillium sp. or Aspergillus sp. We don't know if the latter molds appeared later in the life of the lumber, perhaps parasitically on top of existing biological materials, but there was no doubt that it was present on new pressure treated wood which we examined both at building supply houses and at some building sites. An example of a parasitic mold commonly found growing on the ophistomoids is Gonadobotryium sp.
Here's another example[photo] showing that a single pre-moldy-2x joist was used to make a built-up basement beam. See this photo of black mold on a built-up wooden girder or beam?
If you are reasonably sure that you’ve got mold like Ceratocystis/Ophistoma that came in on the lumber at time of framing, it’s harmless and also is not likely to grow into a bigger problem. In fact indoors we have never found Ceratocystis/Ophistoma mold in an active growth state inside of a building – we imagine that it needs different (wetter) growing conditions than found in a building. Indoors, even if Ceratocystis/Ophistoma mold was alive, it’s cosmetic-only.
Cleaning or removal of a cosmetic mold is entirely optional and would be done (or not) in a building for reasons of appearance, not health.
Leave Cosmetic Mold Alone on Dry Indoor Framing Lumber
If the cosmetic mold you see is like that in our photographs on this page, that is, there is no evidence of active mold growth and the mold obviously came from the lumber yard and the lumber is dry, or kiln-dried, and the environment where the wood is found has remained dry, the mold is only cosmetic and no action is necessary.
Clean Moldy Pressure Treated Framing Lumber that is to be Used Indoors
When using pressure-treated lumber for interior framing, clean off any visible mold. Simple power-washing would suffice
This step is not necessary and would be inappropriate for the same lumber when used outdoors, such as for a deck or an entry stair. But inside, such lumber may be used for sill plates or in some cases we have seen it used to re-frame a rotted floor over a wet crawl space.
Importing a large Aspergillus sp. colony on the floor framing surface over a crawl space provided an immediately-detectable high level of airborne Aspergillus sp. in the room above this area, as these spores move easily in convection air currents moving from the crawl area up through the building.
For this reason, if visibly moldy treated lumber is to be used in indoor construction we recommend that it be physically cleaned first - such as by using a power washer and deck cleaning solution. "Sterilizing" such lumber to try to "kill" mold is unnecessary and inappropriate.
Just clean the moldy lumber, don't try to sterilize it.
See MOLD KILLING GUIDE for details of why killing mold is not the most useful approach.
What if I remove "cosmetic" indoor mold and it reappears? If you remove a mold you believe was "cosmetic" and later you find new mold growth in that area:
ANY indoor building condition that produces or has produced new or recurrent indoor mold growth on building surfaces means there is also a risk of both visible and hidden problematic molds of genera/species other than just cosmetic molds. Even when you test and identify a specific mold on a building surface you should not assume that the mold you've identified is the only problem, or even the most serious mold problem in the building, unless you have also completed a through, expert diagnostic inspection of the building.
To prevent problem indoor mold your focus should be on watching for and correcting leaks or moisture problems in your building. For details on how to prevent indoor mold growth in buildings see:
In summary about cosmetic indoor mold: If at present you’ve found evidence of mold growth inside of a building other than Ceratocystis/Ophistoma then it’s moisture and leaks that need your attention, not the Ceratocystis/Ophistoma.
Recently I was in the process of selling my home, a 1958 brick ranch with basement daylighted on all but one side. In selling the house the buyer’s inspector made note of mold on the floor joists over the basement which of course immediately scared of the buyer because the inspector didn’t bother to explain molds, types etc.., I am not sure he did any testing only a visual.
I am certain from looking that it is the harmless cosmetic mold you mention in some of your articles that often begins when wood is brought to the job site etc.
It shows what you call in some of your articles interrupted mold growth and has been on the joists for the full 10 years I have lived in the house without any growth etc.., I am sure it has always been on the wood and the dust accentuates it. In fact, my inspector when I purchased the home said it was normal.
The basement is completely dry even in what has proven to be a very wet season this year.
However, now I am in a dilemma since the one inspector has made mention of mold. Should I test and treat it? If I have it tested and its harmless type can I treat it myself or now that it has been noted should I have a professional to do so? Any suggestions on how I get around this becoming an issue for future potential buyers?
In my opinion this is one of those cases where I wish the general public was more educated and the inspectors would be more thoughtful not to generalize. I fear this will keep my home from selling.
Any thoughts and advice would be greatly appreciated. Also if you have recommendations of reputable companies in Atlanta that won’t take advantage I would greatly appreciate that as well. - Anon. 9/4/2013
Reply: do we need to inspect & remediate a mold problem or not? Should every house be "mold tested??
You want your buyer to be fully and accurately informed - a step that protects both buyer and seller from surprises, but indeed some less-experienced or nervous inspectors, or folks who just don't know about a topic may protect themselves from a complaining client at the expense of accuracy - no one is well served by shortcuts: the community's time and money may be wasted.
Watch out: Mold "testing" is often not really justified and more often is not conducted in a way that gives accurate, reliable results anyway; but if a large area of visible mold is noticed, it should be called out to avoid a scary or costly surprise later.
The "interrupted growth" pattern is pretty obvious and along with the appearance of the moldy surface and other details often is enough to avoid any panic; but not everyone agrees. I had a client who was furious with me when my inspection (and lab tests) confirmed that a "black mold" in his home (on wood framing) was cosmetic and did not require a multi-thousand dollar demolition that he wanted to make.
"Truth," he said, "should not get in the way of my remodeling job. I need this finding to get insurance coverage."
Should Every Home be Tested for Mold?
Without seeing your site and having more data I can't give certain advice; for example on occasion I've found harmful mold growing happily atop cosmetic mold - in particular on damp pressure-treated lumber, and on occasion on wet framing in an existing building indoor area. Without some basis (leak history, building IAQ complaints, inspection by an expert, perhaps a simple supporting lab test of representative moldy surface) I would NOT treat the mold; that step risks
I just can't support recommendations to perform expensive inspecting and testing for every "mold alarm" that is raised.
At MOLD / ENVIRONMENTAL EXPERT, HIRE ? we include some suggestions on deciding when such investigation is warranted.
In sum, if I were selling a home and encountered a buyer wary of a suspected mold problem, and if that were causing a stumbling block I'd perhaps be forced to ask for an independent and truly qualified expert who could take enough of a look (and possibly some surface or dust tests) at the building that we could decide if there were an actionable problem or not. That person should be paid by the buyer so that there is no worry of conflict of interest; you can give-back that fee at the sale closing if you prefer. Check with your attorney.
IF there is no real basis for a proper and reliable mold inspection - i.e. the appearance is of only cosmetic mold, there are not water, moisture, IAQ, or health complaints nor such history, etc. - then a qualified or competent expert ought to be able to reach that conclusion by an onsite inspection of the building (outside and in) along with a taking of building & occupant history.
If Mold is Found is Expert Remediation Needed?
If an inspection finds indoor mold contamination, that is other than "cosmetic" mold, and if there is more than 30 sqft of contiguous problematic indoor mold, then it's proper to have it addressed professionally and to have a final clearance inspection;
If not, a DIY cleanup or cosmetic treatment is normally adequate, with the proviso that if during cleanup a larger problem is discovered work stops to bring in a professional. Beware of capture errors: someone focusing on (perhaps harmless) mold that is seen in a building may fail to miss more urgent building health and safety concerns - more people are hurt by falling down the stairs.
Watch out: Beware also of consultants who take the "safe" course of spending more of other people's money to reduce risk to the consultant. If you want to send along photos of your situation as well as text from the inspector's report so that we know what s/he actually saw and reported, I may be able to comment further.
It is a 3 sided daylight basement, very dry (included picture of cmu wall also, hopefully you can see dry cmu walls from that, the basement itself is not wet at all) and the picture you see also has much dust on it. Once the dust is wiped off it is much cleaner but the darker coloration is linear in fashion in the wood (black and green), wood is solid etc.., very little if any musty smells.
Our intent was to wipe it down carefully with DIY using baby wipes or similar that can be wiped once and bagged.
Our biggest concern is now that it is on a report as mold (most likely only from visual inspection) we will have to hire a professional to ensure protection for potential future buyers.
Maybe I am wrong but I believe this inspector has made a much bigger deal out of something that probably should not be. My believe is at best he should have made a notation that there is potentially mold…, until which time we could have had it evaluated.
Any suggestions you have on how we should best proceed to correct any problems and secondly to protect from the mold scare of future buyers would be greatly appreciated.
I'd be careful: on T&G pine subflooring I do find a variety of fungal growths; your photo is not super sharp - I can't assert this is cosmetic-only. Problem mold conditions can occur from even a single event in a building's life even if the building has not regularly flooded. Even during construction.
Take, or have a neutral third party take a couple of tape samples that you and the neutral party agree are representative of the substance found in wide areas on the subfloor and joist sides; If there are multiple-colors, then take more than just 2 samples (one subfloor, one joist) - one per color or texture difference.
You can mail to me up to 4 samples for lab analysis - I'll process them pro-bono as a courtesy and to avoid any issue of conflict of interest, and will report to you what I find in the samples.
To make sense of such a report you need good evidence that where you collected the samples does represent the areas in question. When I've done such tasks I photo-documented the sampling location, labeled tape on the surface, and I kept a control sheet identifying each sample.
Physical wiping and HEPA vacuuming; any household cleaner is fine. You're not trying to make the area sterile, just get rid of a potential problem particle. Using disposable wipes improves the cleaning process as you reduce the spread of debris from the first wipe stroke to the second. But it may be overkill. Clean the surfaces.
If after cleaning you want to use a clear sealant or fungicidal sealant that's ok though not necessarily required. Sealing wood immobilizes remaining particles and reduces moisture uptake, so reduces the propensity to support mold in the future.
Use the procedures found at http://inspectapedia.com/sickhouse/Adhesive_Tape_Particle_Test.htm - it's quite easy - and just include a copy of our email correspondence with your samples. Please do NOT send samples in any other form than described in that web article unless we have discussed them first. We will examine your samples in our forensic lab and email you a report with our observations.
Keep in mind that in some buildings there may be no visible mold or the visible mold that you see may not be the most significant mold reservoir or problem there. Similarly, people may have building-related complaints where there is no mold or other particle hazard present at all. Finally, small amounts of indoor mold, of just a few square feet, if that's all that is present, would be very unlikely to explain a building-related health complaint.
Small areas of indoor mold can usually be cleaned by just about anyone using ordinary household cleaners.
See DO-IT-YOURSELF MOLD CLEANUP WARNINGS for details.
How to Get Rid of Sapstain or Blue Fungal Growth in Wood
Reader Question: I am a chainsaw carver who deals with blue fungi mold in logs - how can I get rid of blue fungal growth on my wood?
I am a chainsaw carver who deals with blue fungi mold in logs; I have attached a photo. Can you provide information on this and getting rid of it; I have numerous colleagues who also like to know! - S.N.
Nice photo, S.N. I can't ID a mold fungus from that or any photo alone (only a fool would claim to). That said, it's indded possible we're looking at a blue sapstain such as Ceratocystis sp. or Ophistoma sp. But before we go messing with bleach - a cosmetic repair that has its own problems, let's run through some diagnostic questions about wood stains and blue sapstain fungal growth in your wood.
1. Let's make sure it's not some contaminant that fell onto the wood, or that a fungal growth is not being encouraged by how wood is stored or by something else left lying atop the wood that traps or holds water. In the photo the stain looks as if it has run from water - was this log slice standing vertically or on an angle?
Normally mold growing on wood would begin from a spore landing on the surface, and would grow often in a rounded pattern out from that point; spores or fungi don't land on wood in a dead straight line.
Sapstain fungal growth (bluestain) may indeed not look random on the wood, as our photo from Winfield shows at left. The fungal growth is probably following the cellular structure of the wood itself from where the first inoculating spore(s) found a home.
Our other photos (below) show additional typical mold growth patterns on wood & lumber.
But something straight that was placed on the wood might indeed cause straight-line staining. That makes me wonder if your stains are in fact being caused by stickers you are using to separate slabs of wood you are trying to dry (stickers themselves are too wet or are a poor material choice), combined with a slow drying process, possibly aggravated by storing your wood exposed to rain and in warm weather. Woodweb discusses sticker stain and provides some excellent advice if this is the root of your stains.
2. Let's do a little testing for wood penetration of the stain. Have you tried cutting a sample with a gouge chisel or knife?
Does the stain extend into the wood grain or is it mostly surface? I suspect you'll reply the stain has penetrated the wood surface (whch these sapstain fungi certainly do.)
3. Does the stain always appear in this pattern on all of your wood samples? Take a look at the example photos I include from our two reference texts.
4. Is this stain in the wood when you buy it or cut down the tree, or is it appearing on the wood while you have it in storage, perhaps drying?
5. I could examine (pro bono) both a wood gouge sample of stained (and a control of not-stained) wood (just a 1/2" square would do) and a tape sample if you can get the material onto a clear adhesive tape.
If you are already certain it's a fungus it's probably blue sapstain such as one of the two species I've cited above, and that I discuss online
My reference texts on this topic, by Wingfield et als, has (p142) sapstain photos in black and white.
I'm posting here copies of some reference in-situ mold on wood photos for your comment (or comments from other readers) along with similar images from Wang & Zabel the other useful text for this topic.  
Remedies for Sapstained Logs, Log Slices, Wood or Lumber?
Unfortunately if the bluestain is deep into the wood it's almost impossible to remove completely. Worse, we have read that some fungi may be present but not visible as a stain until the wood has been further dried & cured.
I've had some success with detergent followed by careful treating with bleach solution, and a thorough washing off a wood surface to reduce or eliminate stains (and bleach odors) in a finished product.
But deep stuff is hard to deal with. Selection of wood not already visibly infected, and prevention of mold growth on stored wood by attending the conditions on which we store it may be in order. I know that may be tough for a chainsaw wood carver, since you work with big sections of logs that remain outdoors. Let's get more confident in our diagnosis and then pursue remedies further.
Blue stain or sapstain prevention (& sticker stain prevention) in or on wood
Handling moisture, both in the wood itself, and in the environment where wood is stored for drying and before use, is the single most effective thing you can do to reduce fungal growth on and in the wood itself. Speeding the wood curing or drying process, including storing wood on separation stickers, off the ground, and under cover (protected from rain and snow but not in an airtight enclosure) could make a significant difference in the rate of bluestain or sapstain occurence on your wood.
If your wood stickers are not absolutely dry (below 10% moisture) they could be causing sticker stain as we discussed above and as I suspected from the stain pattern in your photo.
If your wood is not stained when you first rough-cut it, you may be able to retard if not prevent sapstain growth by dipping the log sections in a fungicidal chemical (or enzyme). The problem is that the wood may be inoculated and your treatment may not penetrate the lumber adequately. That's why pressure-treated wood is "pressure treated" (though the pressure treatment target is not fungi and the chemicals used don't seem to retard fungus growth in that case).
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