This article describes how to identify and diagnose carpeting stains at the edge of carpets near walls in buildings focusing on the cause of various interior wall and ceiling stains and explains how to recognize thermal tracking, thermal bridging stains, building air leaks, and building insulation defects.

We explain what these particular stains look-like, why they occur, and how to stop them.

Air Leak or Ghosting Stains & Marks on Carpeting - a Diagnostic Guide

- Daniel Friedman & Alan Carson, Carson Dunlop, Associates, Toronto

Building Air Leaks & Thermal Tracking Marks on Floor Carpeting Near Walls

Skipping for a moment stains on carpeting that are due to spills of food, drink, or other stuff, and skipping pet stains from "accidents" on the rug by your dog, cat, or other pets, there are several common sources of carpeting stains and marks worth recognizing as they can tell us something about building conditions that may need attention.

Carpet stains from thermal tracking, air leaks, or areas of higher moisture that cause collection of house dust, candle or fireplace soot, heating system soot, may appear out of the normal walking-traffic areas.

If there are air supply registers in or near floors, air movement from the HVAC system may also deposit dust that appears as sooty stains around and close to the register.

Black or dark sooty stains on carpeting can appear from foot traffic but those marks will appear in the main walking path through a carpeted room.

Al Carson, a home inspection educator and researcher, has pointed out that we often see dark marks at the edge of floor carpeting where it touches or is close to wall baseboard.

These marks are likely to be most severe where the carpet meets exterior walls.

These carpet stains at walls occur most often on the lower floors where we get infiltration (air moving in to the building space) from the basement or crawl space below. It is the counterbalance to the ex filtration (air moving out of the building space) issues found at the attic level.

As outdoor, basement, or crawl space air leaks into the building around wall-floor intersections, the edge of the carpet acts like a filter and collects dirt from the air leaking in.

These carpet stains are not mold:

Some people mistake these "carpet edge stains" for toxic "black mold".

If the carpet stains are pretty much continuous along the floor/wall juncture of carpeting and not elsewhere, and particularly if they do not appear elsewhere and are not related to other building water leaks, it is not very likely that these stains are mold.

About these photographs of carpet stains:

Thermal tracking or "soot tracking" is visible along the wall baseboard in the photograph at page top - notice that gray line about an inch wide along the carpet where it meets the wall?

The more ugly dark brown stains at right angles to the wall are not thermal tracking but indicate that this floor was wet, causing rust or bleeding from a cabinet which had been placed in this location. This photo is therefore interesting (if a bit confusing) because it shows two different types of carpet staining.

High indoor humidity:

If indoor humidity is excessive (say regularly over 50 or 55% RH) we may be encouraging mold growth in a building or we may be inviting excessive levels of dust mite activity which in turn increases the level of allergens in the building.

Usually soot marks, thermal bridging, or thermal tracking stains appear, if at all, in the building interior locations discussed in the remaining sections of this article.

Where Do Air Leak or Thermal Tracking Carpet Stains Appear?

• At the edge of carpeting along exterior walls
  
  where floor-wall gaps are common in all types of construction: slab on grade, crawl space, basement, or multi-storied apartment or condominium buildings.
• At the edge of carpeted floors along interior wall partitions
  
  over a basement or crawl space, again if floor-wall gaps are present.
• At or near heating or cooling air supply registers
  
  that are in the floor or are close to it; possibly, but less common, also at air return registers located in or close to floor level.
• Under furniture or in other areas of peculiar drafts
  
  or air movement that may carry and deposit dust or stain particles on cooler or more-moist areas of the floor.

Carpet stains from thermal tracking, air leaks, or areas of higher moisture that cause collection of house dust, candle or fireplace soot, heating system soot, may appear out of the normal walking-traffic areas.

Black or dark sooty stains on carpeting can appear from foot traffic but those marks will appear in the main walking path through a carpeted room.

Watch out: thermal-tracking-like stains on carpeting also appear along building exterior walls where there are air leaks, and may also appear as black streaks or smudges on ceilings and walls.

Carpet stains at edges of or under furniture

Carpet stains due to air movement, possibly exacerbated by higher moisture where there is less air circulation, may occur under couches or other furniture whose skirts or other construction details interfere with air movement, causing a lower temperature (and possibly slightly higher moisture condensation) in those areas.

In our photo at above left you can see the mark from a couch foot near the right side of the photo, cleaner carpet exposed below a floor runner, and darker stained carpeting that developed below this piece of furniture.

Blotchy carpet stains: When the furniture is moved the differences in carpet color or actual carpeting soiling and stains may be very obvious, especially where a couch skirt was in place.

Occasionally we also see more blotchy carpet stains with sharply defined edges where a spill has occurred or where a partial attempt was made to "wash" an area where thermal staining had previously occurred.

In this photo at right side a vertical dark line probably marks where a couch or chair skirt was in place.

[Click to enlarge any image]

Usually lab testing is an unnecessary approach when removing or diagnosing stains or contaminants on carpeting but sometimes when visual inspection and considering building history (leaks, spills, pets, air leaks, puffback or other soot producing events) isn't enough and where significant expenses are involved in cleaning or replacing carpeting we might test tape or dust samples of the carpet stain area as well as other samples of settled building dust.

What Should We Do About Dark Black Shadows on Carpeting Around Walls or Furniture?

Reader Question: We have a problem that none of our local "experts" (builder, carpet cleaner, pest guy) have any idea about or have ever seen. It presents as dark/black shadows around walls or an object that has laid on the carpet floor for awhile (months).

Our HVAC filters get black in It is very hard to get up. It is like something embedded in the carpet fiber. It occurs more upstairs than down.

The house is 4 years old, no pets, two adults, no smoking, in a new development in inland South Carolina, no apparent moisture problems, heat pump upstairs, gas down. [Photo at left].

We need advice on what to do. - J. B.

Reply: Decide if the Stains are Abnormal, Identify Probable Particle or Debris Sources, Correct the Source, Clean the Carpets

The fact that the dark stain is in such a straight line suggests that furniture or something else placed along the wall was protecting the "clean" area of carpeting from airborne soot or debris deposits, just as you suspect.

Start by taking a look at the common indoor stain types and sources we describe

at STAIN DIAGNOSIS on BUILDING INTERIORS - that might explain what you're seeing on your floors.

It's useful to make a distinction between dark stains that occur on carpets, floors, walls, ceilings due to deposition of ordinary house dust due to thermal tracking and stains that come from an abnormal or avoidable or even a potentially unsafe source such as gas fired heating equipment that is not working properly, leaks, or mold.

See THERMAL TRACKING & THERMAL BRIDGING

Also, from your description I wonder if you have a soot source - is your heating system oil-fired? Or worse, if it's gas fired and making soot that's very dangerous and needs immediate attention.

Watch out: soot produced from gas fired heating equipment of any kind is potentially very dangerous, even fatal, as it's a symptom of improper operation and possible carbon monoxide production.

Next Step: Initial Theory of Where the Soot Stains are Coming From: Ventless Fireplace

Here's our theory: The "dust" is soot from the gas pilot light in the downstairs ventless fireplace. It has been on since November. Off for a week. I have a filter element, installed in November, from the downstairs AprilAire that is black. The downstairs heat is gas - checked out OK last week.

Upstairs HVAC is a heat pump, also checked OK. Upstairs is little used, the heat/fan is normally off. House has always been dusty, not this black color. The soot floats upstairs and is conveyed down to the carpet by local downdrafts, against the cooler walls.

Anything in the way creates unusual patterns. Inside surface of all windows in house - black when cleaned. Outside not, garage not.

Does that theory make sense? How do we prove it? Should I send samples? If so, what's the procedure, how many, from where, cost?

Most important, how do we clean? A paid attempt, local ChemDry franchise, had never seen anything like it, wasn't sure that they could get it all out - didn't.

Reply: Correct apparent soot sources, check for other unsafe soot sources, clean, monitor

Your theory sounds plausible though without the benefit of expert onsite inspection of course one can only speculate.

Black looking carpet stains can be comprised entirely of house dust, or if as you may have done, you can find a source of soot, that is a likely particle source.

Part of understanding carpet "soot" stain diagnosis is the determination and interpretation of the stain location, pattern, and even time of appearance.

For example, if the stain appears only at the perimeter of building exterior walls we pose that that may be due to lower temperatures at the floor/wall juncture or even air leaks there.

I also agree with you that cooler exterior walls can cause downwards air movement in that location, depositing building dust or soot along the wall/floor juncture.

Other dark carpet stains such as in your photos can track to the location of furniture that has protected the not-stain area from particle settlement. Often we find darker carpet stains behind furnishings than in the occupied and walked-on space, perhaps also because those areas are less easily and less often reached for cleaning.

But your discovery of sooting at the gas pilot light on the ventless fireplace that has been sooting since November sounds to me like a good guess at a source of extra soot particles in the home, and your observation of a sooty deposit on windows supports that view too.

Set Priorities of Attention: Safety First

In terms of priority of attention and action, any gas appliance that is producing soot is potentially a dangerous carbon monoxide or combustible gas leak. So a first priority (after simply turning off the gas to the ventless fireplace) is to have that system examined and repaired to a safe condition.

I doubt that soot production is normal.

Watch out: see also CARBON MONOXIDE GAS

Is Carpet Stain Testing Appropriate?

While it is possible to collect suspect particles such as black carpet debris by using a vacuum-operated sampling cassette or even by careful use of clear adhesive tape, and while that same tape approach can be used for window surface debris, in my OPINION testing may not be warranted.

See CARPET STAIN ID TESTS

and CARPET CONTAMINATION TEST PROCEDURE

While particle identification would certainly be technically interesting (and a forensic lab fee may be as little as $50 or $100), even if a significant component of the dark carpet stain particles are identified as soot, we should not assume that the source you found is the only or most important one - not before performing a more thorough inspection of the building and its mechanical systems.

In other words, while we love particle testing and identification (I operate a forensic microscopy particle identification lab), you should not use a test or two as a substitute for a thoughtful inspection of the building. (It took thought to track down that fireplace as a soot source.)

What to Try Now

If you agree that lab testing is not really necessary, you might prefer to spend your money and energy on

I'm not sure just what process the local carpet cleaner used, but I agree that if it was ineffective, you need to try something else. Sometimes we find that a stain that is very resistant to one approach is removed easily by another.

A client spent a large effort using solvents to try to remove some brown goop that we thought was tile mastic. When she tried using plain water the goop came up easily - it was water soluble but was resistant to other solvents.

Cleaning of the carpeting: you may need to hire a carpet cleaning service that uses steam or even a rug shampoo and water extraction procedure. I'd avoid really wet carpet shampooing or any process that soaks or wets wall to wall carpeting if possible.

Discuss the suspected type of stain and what was tried before with your new carpet cleaner in deciding what cleaning process is necessary.

Inspecting all other gas-burning appliances in the building to be sure that they are operating safely and properly

I'm not sure what portable air cleaner model you have been using but our experience is that while a portable air cleaner will remove some indoor air particles, there is no evidence that those devices move and process enough air to remove high levels of airborne particles throughout a building.

However, if your home has central air heating and/or air conditioning, check and maintain your air filters.

See AIR FILTERS for HVAC SYSTEMS.

If the sooting is from a problem source and not simply the common room perimeter carpet staining that occurs in buildings due to air movement, cooler wall/floor junctions and normal house dust deposition, and if you clean the carpets and fix the soot or debris sources you can find by inspection, there's a good chance that the problem will not recur.

If unusual carpet sooting stains recur, then further inspection and perhaps even testing would be appropriate.

 

Thanks to Alan Carson, Carson Dunlop, Associates, Toronto, for technical critique and content suggestions regarding thermal tracking and its appearance on carpets as well as building walls and ceilings.

• 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 TRAINING,        Horizon INSPECTION SOFTWARE    &    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.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-10-19 - by (mod) -

Maggie

What I see in your photo is foam carpet padding

and along the edge of the floor at the wall, cracked material that might be old vinyl floor tiles or we might be seeing cracking along the edge of a concrete floor slab - I can't see enough in the photo to be sure.

On 2020-10-18 by Maggie

Does anyone know what this is? I pulled up my old carpet so I can install new carpet. And this is what I found. Mostly on outside walls.

...

Continue reading at CARPET STAIN DIAGNOSIS - home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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• CARPET STAIN DIAGNOSIS - home
  • CARPET AIR LEAK STAINS at WALLS
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• STAIN DIAGNOSIS on BUILDING INTERIORS - might explain what you're seeing on your floors.
• STAINS on INDOOR SURFACES, PHOTO GUIDE
• THERMAL TRACKING & THERMAL BRIDGING - home

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