A Photo Guide to Stains on Indoor Surfaces in Buildings InspectAPedia® -
A Photographic Guide to Diagnosing Indoor Stains on Carpet, Cabinet Doors, HVAC Registers
Phantom stains - indoor marks that are not an actual dirt, debris, or mold stain
Guide to stains and debris around heating and cooling air registers and baseboards and on air filters
How to diagnose discoloration, stains, or light spots on indoor carpeting; moldy carpeting?
Links to more photos of indoor ceiling or wall stains that are not toxic mold
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This article describes, provides photographs, & diagnoses the causes of interior wall, ceiling, flooring or carpeting stains and explains how to recognize their probable cause and source, including
soot stains, house dust stains, pet or animal stains, and thermal tracking or thermal bridging stains associated with
building air leaks, and building insulation defects. Readers should also see STAIN DIAGNOSIS on Indoor Surfaces and for outdoor stains, see Stain Diagnosis on Building Exteriors. Also see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES where we discuss not only moss and lichens but black fungal stains on asphalt shingles and on other building surfaces.
Often these stains are mistaken for toxic indoor mold. When investigating a building for a mold problem, you can save mold test costs by learning
how to recognize Stuff that is Not Mold or is only Harmless Mold but may be mistaken for more serious contamination
- save your money. Because some clients have on occasion sent
samples to our mold test lab that really should not have been collected, much
less looked-at, we provide this library of photographs of things that are "not mold" and don't need to be tested.
"black mold" often mistaken for "toxic fungal growth."
Photos of HVAC and carpet stains (excluding the moldy carpet photos) were provided courtesy of Pat Belkin, Charlotte, NC.
A Photographic Guide to Help Diagnose the Causes of Indoor Stains on Carpet, Cabinet Doors, HVAC Registers
Here are some examples of troubling indoor surface stains with some preliminary opinions about what these stains may be
about. We emphasize preliminary opinion because here we comment on these photos before an expert diagnostic building inspection
has been performed and before any lab samples have been collected and analyzed from these surfaces. Whether or not such sampling
and analysis are justified depends on the experience of the building occupants (health complaints or health vulnerability),
the history of the building (exposure to leaks, damage, pets, contaminants), and other site investigative results. See When to hire a professional to investigate a building for
help in deciding when to go further.
How to Recognize & Diagnose Phantom Stains on Indoor Surfaces
Often when people become concerned about indoor air quality, mold, or stains, they begin to study their building surfaces more carefully than
ever before.
When this happens we sometimes find people reporting as "new" stains that were there from original construction, but where simply not
noticed, or were not so particularly noticed before other concerns increased their level of attention.
This interesting photograph of a large
yellowish stain on the surface of what appears to be a birch kitchen cabinet door surface (probably the door's interior surface)
could be an example of this phenomenon.
What would support the "phantom stain" hypothesis for an item such as this cabinet door?
Stain pattern: If the stain appears in a regular pattern on companion surfaces such as other cabinet doors it may be an artifact of the door's manufacture
Stain location: If examination of other cabinet surfaces shows similar stains in varying locations
Manufacturing artifacts: If examination of sample cabinets from the same supplier or manufacturer, new, say in a showroom, show similar markings
Ability to remove surface staining material: If a tape sample cannot remove any debris from this are of darkened color
Stain particulate or chemical components: If a tape sample of surface debris removed particles which are determined to be finish coatings or wood fibers without fungal or chemical modification,
Presence of common causes of stains: If there are no moisture, food, air movement, or other suspect sources that have affected some of these cabinets but not others
Time of occurrence of stain: If the stain is under the finish-coating of the wood cabinet surface rather than something which was deposited on top of the coating (though indeed moisture can in some circumstances affect surfaces below their coating)
then this may be the case with this example photo of a yellowish stain on a birch ply cabinet door interior
How to Diagnose Stains & Discoloration on Heating or Cooling Supply or Return Registers or Plenums
Supply Register debris: The left photo above shows typical house dust deposition on a heating or cooling ceiling air supply register, where you can see brown
debris adhered to the metal register surface. These particles adhere to the register surface due to either moisture from condensation or
in this location, more likely due to static electricity as particles are moving across a normally dry surface.
What to do about supply register debris: House dust, normally composed primarily of human skin cells and fabric fibers, is not
usually an environmental or air quality issue, though at high levels on surfaces it can be diagnostic of building conditions such as high moisture
or poor HVAC system maintenance.
We can reduce this debris deposition by duct and air handler cleaning and by better and constant maintenance of filters at the return air registers.
If other information disclosed by the building investigation warrants, one have this debris screened for mold, allergens or other problematic particles by using
a forensic laboratory whose technicians are expert in house dust analysis.
Return register & return air plenum debris: The right hand photo shows a combination of
paint overspray (white particles on the black return plenum insulation liner), and house dust (brown debris on the metal frame
intended to hold a return air filter).
What to do about return plenum debris: The brown dust and debris indicates that the air filter used at this
location has been leaky. See An Analysis of the Effectiveness of Air Filters on HVAC Systems
for further advice on air filters that do not leak in this location.
How to Diagnose Stains & Discoloration on Heating or Air Conditioning Filters
Air filter debris: This home air filter was taken from the central return air plenum and register cover shown in the photograph just above.
The brownish stains on the filter are a typical color (brown to gray) of debris found on any indoor air filter. Such
"stains' indicate that the filter is doing its job of reducing the level of airborne debris in the building.
What to do about air filter debris heating and air conditioning filters should be changed at least monthly whenever
this equipment is in operation. In a dusty environment more frequent changes may be needed.
Also see An Analysis of the Effectiveness of Air Filters on HVAC Systems
for further advice on air filters that do not leak in this location and also
see When to hire a professional to investigate a building for
help in deciding when to go further in inspecting, diagnosing, and testing particles and debris on a building air filter. In many
circumstances further testing would not be justified.
How to Diagnose Mold Stains & Mold Growth on Floor Carpeting
These photographs show two common patterns of mold growth on the upper surface
of a carpet that was left wet in a building. In the left photograph a brown mold is growing
in a rather uniform pattern without definite edges on carpet in a closet. The black mold
visible in the upper left and right portions of the photograph will probably be a different
mold genera and species - this is an example of the dangers of careless sampling of mold in buildings
since a lot of what people think is present in a building depends on exactly how mold samples are
collected.
The right hand photo above shows two rather round black patterns of mold growth on floor
carpeting in the same building. Even if no mold was visible on other carpet surfaces in
this building it is likely that the carpeting, if it was wet, has become mold contaminated - a condition
that might be confirmed by inspection of the carpet backing, padding, or other building surfaces.
Even carpeting which has not been wet may be a significant problem mold reservoir in a building
if the carpeting has been exposed to a high level of airborne mold or other allergens. This condition occurs,
for example, when a water-damaged moldy building has been remediated without proper dust and debris control.
Screening samples of carpeting and other building surfaces taken outside of the remediation work area
both before and after a mold remediation project can protect both the remediation company and the building
owner from unanticipated additional mold cleanup work after the initial mold remediation project has been
completed.
How to Diagnose Stains & Discoloration on Rugs or Wall to Wall Carpeting
Possible thermal tracking stains are shown by the darkened debris on the floor carpet in the
left photo above, where a grayish line appears to follow the point where the wall to wall carpeting
abuts the building wall or wall baseboard trim. See Thermal Tracking for
detailed discussion of this phenomenon and how to diagnose it.
Possible furniture footprint stains on carpeting are suggested by the right hand photo above. Sometimes
a stain like this, particularly where it follows the same shape as an object which has been placed on the carpet,
suggests that the stain was deposited from the object itself, or dirt on its surface, or bleed-out if the object
was placed on a carpet left damp after carpet shampooing.
How to Diagnose "Clean" Areas of Carpet Surrounded by Stains or Discoloration
"Clean" areas of carpet under furniture can also tell us what's been going on in a building. In the
right hand photo above, the carpet appears darker inside the stain perimeter which suggests that
the mark we see is either from a spill on the carpet or from the footprint of an object which was placed on
the carpeting. But if a mark on carpeting outlines an area of carpet which is lighter or cleaner than
the surrounding carpeting, we usually find that an object which had been placed on the carpet was actually protecting
that surface from settling dust, soot, or other debris in the building.
In this case we'd look further for an indoor source of high levels of airborne soot or other debris, such as
a malfunctioning gas or oil fired heating system. Because such system could be unsafe, the inspector should be
one who is quite familiar with inspection methods and indicators of an unsafe or improperly-functioning
heating or cooling system.
Usually soot marks, thermal bridging, or thermal tracking stains appear, if at all, in the building interior locations listed just below discussed
in the remaining sections of this article.
Online Guide to Types of Stains on Building Roofs, Surfaces, Walls
In the following guide we list types of stains by stain color & appearance, by building location or material, and by stain cause. We distinguish among the following stuff that may stain or be found growing building roofs, walls, or other surfaces, with extra focus on asphalt shingle roofs as well as other roofing materials such as wood shingles, wood shakes, roll roofing, and even slate or tile roofs. Some of these types of roof stains or discoloration are only cosmetic in nature, while others may indicate growths that are likely to reduce the roof covering life. A more detailed, illustrated version of the list below is given at Stain Diagnosis on Building Exteriors.
Black stains on asphalt roofing products such as asphalt shingles or roll roofing, caused by extractive bleeding (product defects) - see Bleed-Through and see Roofing material defect / environmentally-caused roof shingle stains.
Black, brown, or gray stains on roofing products due to debris left on the roof surface, such as piles of leaves and organic waste from nearby trees. See Debris Staining and see Proximate cause roof shingle stains
Black or other colored stains on roof surfaces may be caused by soot from chimneys, both wood-fired and oil-fired devices. Black or other colored stains may also appear on roof surfaces from nearby industrial activities. See Soot Staining.
Brown or red stains on roof surfaces are often caused by rust from wearing steel flashing or other on-roof metal products. See Rust Stains on Shingles.
Lichens growing on roof surfaces - Lichens are not the same growths as moss or algae, and are difficult to remove without damaging the roof surface. See Lichens on Roofs for details about how lichens can cause roof damage, see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES for a guide to preventing these roof growths and stains. Also see ALGAE, FUNGUS, LICHENS, MOSS COMPARED.
Moss on roof surfaces - see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES. Green or other colored mosses are a bit easier to remove than lichens on roofing surfaces, but both can carry away mineral granules and damage the roof surface. Moss tends to hold more water and moisture on the roof surface. So in our opinion moss is more likely to damage a roof surface than lichens or algae. Also see ALGAE, FUNGUS, LICHENS, MOSS COMPARED.
Rust Stains on buildings - see Rust Staining - Red or Brown Rust Stains (on shingles)
Soot or Creosote black or brown stains on roof surfaces near or below chimneys - see SOOT STAINING - Black Soot Stains on Roof Shingles Around Chimneys and see Proximate cause roof shingle stains
White stains on roof surfaces may be from wash-down of pigments in paint on surfaces above the roof such as a gable end or dormer wall; white or less-black roof surfaces may also be found below copper or aluminum flashing whose salts run down the roof surface in wet weather, preventing algae or moss growth and leaving a white area on an otherwise stained roof surface. Our article at ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES includes a photograph of this condition on a wood shingle roof.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.
Thanks to Pat Belkin, at Flooring Solutions for providing many of the photographs and suggesting some of the questions addressed in this web page article
We welcome more thermal tracking, soot tracking, air bypass leaks, and similar photos of indoor stains as well as text suggestions to expand this detail and would be glad to credit contributors.
Insulation Identification Photographs - Fiberglass insulation photos, yellow, pink, green, white fiberglass identification in building attics, walls, ducts, other locations
Ice Dam Leaks in building attics and roof cavities, how to inspect for evidence of leaks, identify causes, and correct bad attic ventilation, improper roof venting, and these causes of attic mold or roof structure damage
Looking for Mold what mold is often found where in buildings - simple technical presentation
Recognizing Allergens: What various indoor allergens look like - identification photos to help identify pollen, dust mites, animal dander, toxic or allergenic mold - Common Mold and other Allergens, Irritants, Remedies & Advice
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.
Animal Allergens: Dog, Cat, and Other Animal Dander - Cleanup & Prevention Information for Asthmatics and regarding Indoor Air Quality.
InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.
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
Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
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