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How to Diagnose Stains: Soot-like & Other Wall, Ceiling, Floor or Carpet Stains InteriorAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• A Photographic Guide to Diagnosing Indoor Stains on Carpet, Cabinet Doors, HVAC Registers
• Links to more photos of indoor ceiling or wall stains that are not toxic mold

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. 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. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

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 beome 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 leftand 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.

A Another case of severe carpet staining due to furniture left on wet carpeting, accompanied by mold growth, is shown in this photograph.

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.

A Severe carpet staining due to furniture left on wet carpeting, accompanied by mold growth, is shown in this photograph.

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 seeis 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.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Daniel Friedman - InspectAPedia.com ^TM Website Author/Editor
• Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and content suggestions regarding thermal tracking.
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
• 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.

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More Information on Finding and Identifying Mold in Buildings and Building Diagnostic Inspections and Repairs

• Attic Condensation and Ice Dam Leaks - Detection and Correcting Venting and Condensation Problems in Buildings
• Insulation Inspections: Insulation in Buildings: Identification, R-values, Heat loss, Insulation Types, Insulation Characteristics
• Asbestos pipe insulation in buildings
• Brick "Insulation" in Building Walls
• Heat Loss Calculations, Insulation Properties, Definitions of R, K, U values, Insulation Design
• How to Detect and Correct Attic Condensation & Prevent Ice Dam Leaks in Buildings
• Insulation Materials as Indicators of Building Age
• Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
• Insulation Identification Photographs - Fiberglass insulation photos, yellow, pink, green, white fiberglass identification in building attics, walls, ducts, other locations
• Insulation Identification Photographs - Cellulose insulation photos, Mineral wool insulation photos, rock wool insulation photos, cotton insulation photos, balsam wool insulation photos
• Insulation Identification Photographs - Vermiculite insulation photos
• Insulation Properties, Table of R-Values, density, moisture permeability, fire safety, aging effects on various insulation materials
• Mold in Fiberglass in Insulation
• Radiant Heat Floor Mistakes to Avoid case history of improper placement of slab insulation and radiant heat tubing
• Thermal Trackingthermal bridging & air leak stains in buildings or on building insulation
• Un-Vented Roof Solutions - How to Prevent Attic Condensation, Ice Dam Leaks, Roof Mold, & Roof Structural Damage in Buildings with Un-vented Roof Cavities
• Vermiculite Building Insulation & Asbestos
• 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
• Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens
• 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.

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

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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