Photograph of thermal tracking on an indoor wall Indoor Stain Removal & Prevention Guide
What to Do About Ghosting, or Thermal Tracking Stains on Indoor Surfaces

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How to diagnose & cure black or dark stains on indoor walls, ceilings, carpets, floors: this article describes what to do about interior wall and ceiling thermal tracking stains, thermal bridging stains, building air leaks, and building insulation defects.

We give detailed step by step suggestions for removing and preventing indoor stains caused by thermal tracking. We include diagnostic procedures to figure out why these stains appear, suggestions for cleaning or painting over indoor stains, and how to prevent their recurrence.

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Indoor Stain Cures: What to Do About Wall or Ceiling Stains, & Un-Wanted Air Movement in Buildings

Photograph of candle soot smudging a wallArticle contents

Question: How do I get Rid of Thermal Tracking Stains & Prevent Their Recurrence

I have what seems exactly how you describe thermal tracking on my ceiling in the living room and some discoloration in other rooms. I live in a twin ranch home in Philadelphia that is quite small/cozy for a family of 8. My question is what do I do to stop this discoloration from continuing? I had someone go into the attic and he said that he never saw black soot in an attic like he saw in mine - it was congregated along the beams of the ceiling.

How do I get rid of it? My furnace was replaced less that 10 years ago by a fellow who has a reputation for his meticulous work - the furnace is also well maintained. We are considering moving and I would like to repaint my house soon. Any suggestions? - P.C.

Reply: steps to remove thermal tracking stains and prevent their return

Below we provider a quick summary of some thermal tracking stain clean up and prevention suggestions, followed by an in-depth article on this topic.

  1. Wash stained surfaces: if your building walls and ceilings have paint in good condition it is usually possible to wash the surfaces, though you may need to make more than one pass to remove streaking, and ultimately you may simply decide to re-paint. Use a non-suds ing detergent intended for cleaning interior walls and ceilings. If cleaning is not sufficient you'll need to re-paint.

    For thermal tracking stains on building insulation in an attic, no cleaning is necessary, just find and fix the air bypass leaks or missing insulation. As long as the insulation has not been wet (and at risk of mold contamination) surface staining from dust deposition by air movement across the insulation won't impact its effectiveness. But fixing the air leaks that left the dust there will indeed improve building insulation and energy efficiency, often significantly.

    Watch out: if you try simply painting over dark thermal tracking stains the black stains may bleed through your new paint job. If necessary use a lacquer primer/sealer paint before your top coat. But before re-painting or even cleaning, some diagnosis of the cause of thermal tracking stains is important since if you don't correct the cause of this staining your newly cleaned walls or paint job may be at risk.
  2. Identify the cause of thermal tracking: review the other sections of this article. Visual inspection of attics, wall cavities, or other building areas can tell you if the building is un insulated or has openings where air is bypassing insulation. Be alert also for building cavities where insulation has become wet and possibly moldy as such would need to be removed before continuing to improve the insulation and air tightness of the home. And don't forget to be sure the stains you are examining are due to thermal tracking.
    See Other Stains on Indoor Walls & Ceilings.
  3. Add insulation to un insulated building cavities such as un insulated attics (first priority) or walls (second priority) and pay attention to areas of air bypass leaks where insulation has been omitted, removed, or imperfectly installed. Identify areas in the building where there are air bypass leaks and seal them.
    Air Bypass Leaks Marks on Insulation
    shows how to recognize where air is moving past poorly installed building insulation.
  4. Seal significant building air leaks against unwanted air movement such as openings at exterior trim, window perimeters, or at the floor/wall or ceiling wall juncture. Thermal tracking stains that mark the location of building leaks or the location of ceiling joists and exterior wall studs are also marking the location of thermal bridging - points of building heat loss. Seal building air leaks and air bypass leak points between building floors. See these articles:

  5. Review the building indoor moisture levels: since even a reasonably well insulated building may develop thermal tracking marks if interior humidity is excessive. If the building has unwanted wet conditions such as a wet crawl space or basement or other areas of leaks, those conditions need to be corrected.
  6. Review and reduce sources of indoor soot or debris such as an oil or gas fired heating system that is not working properly, since those conditions need to be corrected for safety and economy of building heating as well. Since excessive use of most types of candles can also produce unwanted levels of indoor soot, if those are a principal source of indoor stains their use should be reduced or eliminated.
    • Is the oil or gas fired heating system operating properly? If not it may be not only smoky or sooty, but also operating inefficiently and worse, it could be dangerous. A sooty gas boiler or furnace is very dangerous and should be shut down and serviced immediately.
      See HEATING SYSTEMS for articles on heating system inspection, diagnosis, and repair.
    • Are there or have there been occupants who were smokers of cigarettes, cigars, pipes?
    • Are there fireplaces or woodstoves that release smoke to the interior?
    • Have people used candles, especially scented candles in the building?
      See Stains from Candles, Woodstoves, Fireplaces
    • Are building occupants smokers? Cigarette smoke is a big contributor to thermal tracking stains, often leaving heavy brown stains on building walls even where other stain sources are absent.

      Most samples of thermal tracking particulate deposits that we examine in our forensic lab are simple house dust: a mixture of fabric fibers and skin cells. These are normal debris found indoors. But more frequent indoor cleaning, HEPA vacuuming, eliminating of or reducing the number of carpets, installation of glass fireplace doors, avoiding burning food on the stove, are additional examples of steps that can reduce the indoor airborne particulate level and thus the rate of staining on indoor surfaces.

  7. Use a better grade washable paint when re-painting stained surfaces. That will make future surface cleaning easier.

Detailed Step by Step Guide to Curing Indoor Stains due to Thermal Tracking

1. Inspect and Diagnose Accurately to Find the Causes of Indoor Stains and Thermal Tracking

If your building diagnosis is not accurate there is a real risk of both wasting money and possibly failing to attend unsafe conditions such as mold contamination or unsafe heating appliance operation and dangerous carbon monoxide hazards. So it is important to determine why the stains are occurring, to rule out or address safety issues, and then we can proceed to a simple three step procedure.

  1. Cure the underlying causes of staining and thermal tracking, such as by addressing sources of soot and dirt, sources building moisture, insulation defects, and ventilation problems. This step is addressed in detail beginning
  2. Clean, seal, and paint the stained areas. This step is addressed in this article, beginning above
    at What to Do About Thermal Tracking and continuing in detail below.
  3. Monitor for any new staining events and diagnose them

To be reliable a thorough building investigation to identify the causes and recommend cures for indoor stains and thermal tracking will examine the entire property, outside and inside, examining all readily accessible areas, examining the mechanical systems, (plumbing, heating, air conditioning), the building ventilation and insulation, and more. Focus of the inspection may be on the sources of soot and debris, moisture, as particle deposition sources, as well as on building conditions that cause particle deposition on surfaces: high indoor moisture, air movement, insulation and ventilation defects.

2. Indoor Staining and Other Cleanup/Removal Recommendations

2.1. Warnings & Advice About Indoor Stain & Thermal Tracking Cleanup Procedures

Warning about harmful mold: if you hire a professional to address building staining and its cause and remedy this is not a contract not to address a mold or air quality investigation which is a more extensive (and more costly) procedure. For this reason significant mold contamination, health and safety risks, and significant mold remediation costs are likely to be faced at this property: these are conditions which were excluded from the scope of a site investigation for stains, thermal tracking, sooting, or heating and air conditioning problems.

Mold investigation: Where a building investigation shows that the property has had a history of leaks or moisture problems, and in some other cases, we recommend that you have a proper mold investigation performed as it is likely that the property faces significant mold cleanup cost.

Mold safety during building repairs: Because moldy materials are likely to be present, it is important that any property cleaning and repairs which you pursue be conducted properly and professionally in order to avoid increasing the safety and health risk to building occupants

MOLD EXPERT, WHEN TO HIRE - provides assistance in deciding when it is justified to hire a professional to inspect for mold and to prepare a mold remediation plan.

ACTION GUIDE - WHAT TO DO ABOUT INDOOR MOLD contains general advice about removing mold contamination in buildings.

2.2. Repair Guide Addressing Interior Surface Stains or Thermal Tracking & Ghosting

Warning about cleanup effectiveness: No cleaning measures will be effective, and the cost of performing them may be wasted, without also addressing causes of building contamination such as water entry, sewage backups, building leaks, and building ventilation defects.

Those defects which a professional inspection was able to identify are addressed at Exterior, Interior, and Mechanical System recommendations below and in the report specific to your building. Others may be discovered.

Cleanup and demolition can begin, but cannot be completed reliably until/unless the building is acceptably dry. If not all suspect areas are addressed it may be difficult to obtain a satisfactory clearance test following remediation work. If leaks or moisture remain or recur there is high risk of a problem.

Here are the basic steps in correcting an indoor sooting or thermal tracking problem

  1. Stop water entry -
  2. Stop excessive interior moisture generation -
    see MOISTURE CONTROL in buildings
  3. Stop improper or unsafe building mechanical system operation or other activities that produce high levels of soot
  4. Correct building ventilation to remove excess moisture -
    see VAPOR BARRIERS & CONDENSATION in buildings
  5. Where you cannot provide building ventilation, be sure that your building is not suffering leaks or excessive moisture sources
  6. Correct building insulation defects -
  7. Replace obsolete recessed ceiling lights and other un-insulated ceiling penetrations

2.3. Guide to Cleaning or Painting of Stained Walls & Ceilings to Correct Stains & Ghosting

  •  Demolition: remove wet, moldy, or water-damaged materials such as floor trim and moldy plaster/drywall where your investigation has found it in the building.
  • Additional removal of stained, soiled, or moldy material beyond that cited in this section should be continued where opened/removed material discovers additional moldy or suspect materials.
  • Remove building insulation wherever it is exposed by  demolition. Remove insulation within 5 ft.
  • Since future repair, demolition or cleaning processes can disclose hidden problems, anyone performing these tasks should, as a matter of general practice, be alert for discovery of leaks, water entry, building damage, mold reservoirs etc.
  • Clean black-stained areas on ceiling and wall drywall using a non-phosphate commercial interior cleaner, after protecting floor surfaces and after moving out or protecting and covering furnishings. 
  • Alternatively you can elect to paint black-stained areas using a stain-covering paint, in which case We recommend use of a lacquer primer sealer. Do not use a latex sealer as stains often bleed through water-based paints and even some oil-based paints. Bin™, or Enamelac™ are trade names of two lacquer primer-sealer paints that work in this application. Proper ventilation and other procedures are necessary for health and safety during this procedure.
  • Following cleaning and/or sealing in the stained areas, your painter can prime and paint the interior room walls and ceilings throughout. We recommend use of a vapor retarder primer paint on the inside surface of exterior walls and ceilings to reduce the moisture absorption into these materials in the future.

2.4. Investigate Stained buildings Further for Hidden Damage due to Moisture or Mold

Before stopping the demolition of damaged or moldy materials, be sure that all areas of known, visible, or most-suspect damage from leaks or moisture traps are opened and investigated. It is important that the extent of demolition continue sufficiently to see that no contaminated, moldy, insect-damaged, or rotted problem areas remain un-addressed.

Otherwise, there is a significant risk that the cost of this repair and renovation could be wasted by having to repeat the procedure later. Examples of such areas we noted during our inspection include:

While there could certainly be other problem areas as yet undiscovered on the building, the following points of extra risk particularly suggested themselves based on observations made at the site or history which was reported for the building. These are areas of further investigation should indoor air quality complaints persist after the remediation measures recommended in this report have been completed.

Wet basement from a point leak outside © Daniel FriedmanOur photo shows surface runoff or roof spillage that has entered a basement by running down the foundation wall. Unless this water source is corrected, the building will continue to suffer from excessive indoor humidity - a contributor to thermal tracking and soot staining.

  • See the exterior and interior observations made during your building inspection, as these correlated with risk of water entry, moisture, mold, and allergens.
  • Also see suggested items for repair or investigation under Exterior Recommendations, Interior Recommendation, Mechanical systems Recommendation beginning at 3.0 below.
  • Leaks at skylights – in the ceiling area below the point of water entry at the skylight, in the ceiling at the top of the wall down-slope from the leak point, and in at least the top of the wall cavity just below this area; if leak damage is discovered by removing drywall in these spots, drywall should be removed to inspect lower areas such as at the floor and in the ceiling of any finished rooms below the floor in the same location.
  • Leaks at walls
  • Leaks at floors – such as in a wet basement, where removal of material around the perimeter walls is necessary to be sure that all of the water entry points have been identified, diagnosed, and corrected.
  • Areas exposed by present or future demolition, repair, remodeling:
    • Back side of drywall on opposing side of abutting wall or ceiling cavities opened for demolition
    • Surface of framing, sheathing, sub-flooring exposed by demolition

These are optional targets for further investigation: I did not find significant leakage evidence or other evidence in these spots sufficient to strongly recommend immediate destructive inspection of these areas, but it may be more economical to address any such findings as part of the current cleanup plan rather than later.

  • Walls behind baseboards or other trim which have been left in place after flooding – if mold is found in these areas the wall cavities need to be opened for further exploration.
  • Other unopened wall and ceiling cavities, particularly in areas that have been wet such as where leaks occurred from plumbing, ice dams, leaks into walls below window sills, at radiators and plumbing fittings (toilet base, leaky or running toilets, fixture drains) wherever such areas of extra risk can be identified by building history or by visual observation

3.0. Exterior, Interior, & Mechanical Systems: Observations & Recommendations To Correct the Causes of Indoor Stains & Thermal Tracking

(Numbers in report text or tables refer to Site or Lab photographs. Please review the annotated photos attached to this report. There you will see important additional details.)

3.1. Thermal tracking diagnosis: exterior observations and recommendations specific to the subject property

I observed exterior conditions which are associated with leaks, high moisture, or other factors which contribute to mold/allergens in buildings. Please review your site exterior photos (in your site investigation report) as they provide additional specific details. These items have or may have contributed to water entry, interior mold in the building. Correct these sources of leaks and moisture to prevent future water entry to prevent mold re-growth.

3.2. General Exterior Recommendations to Stop Indoor Thermal Tracking Stains & Moisture Problems

  • Maintain the gutters (loose, wrong slope, clogged, leaky), add drip edge or re-hang gutters if roof runoff runs behind gutters; extend downspouts at least 6ft. from the building and to locations that will drain away from the building; assure buried downspout lines are not clogged or leaking underground; correct improper in-slope grade which holds water against the foundation.
  • Repair damaged, leaky exterior components and openings: doors, windows, chimneys, and roof penetrations.

4. Interior Inspection & Recommendations to Stop Indoor Thermal Tracking Stains & Moisture Problems

4.1. Interior inspection and recommendations specific to the subject property:

Besides items already cited above for cleaning or removal, I observed these interior conditions which are associated with mold/allergens in buildings. Please review your site interior photos attached to your thermal tracking and building inspection report as they provide specific details.

4.2. General Interior Recommendations for Removing & Preventing Indoor Thermal Tracking or Ghosting Stains

  • Provide proper attic venting - install continuous, un-blocked soffit and ridge venting; add baffles at eaves wherever insulation blocks intake venting;
    See How to Detect & Correct Attic Condensation
    Prevent Ice Dam Leaks in buildings -
  • Complete missing attic insulation; remove/replace any insulation which appears dirty from rodent infestation.
    See How to Inspect Building Insulation & Ventilation -
  • Dry out all building crawl spaces and keep them dry - see our details about how to dry out a problem crawl space at How to Dry Out A Problem Crawl Space
  • Wall to wall carpeting in the basement/below-grade level creates an ongoing risk of forming a mold reservoir. At the next event requiring cleaning or renovation, we recommend elimination of this material at this location, going to tile or vinyl flooring. Area rugs can still be used as these can be cleaned.
  • Fiberglass insulation in the basement/below-grade level creates an ongoing risk of forming a very significant mold reservoir – this is a condition I have been detecting frequently in buildings, even where the insulation looks clean to the eye.

    At the next event requiring demolition, cleaning, or renovation, we recommend elimination of use of ordinary fiberglass insulation in moisture-prone building cavities such as basement walls against below-grade foundation walls. Use solid foam insulation products which do not themselves absorb moisture and which are less mold friendly.
  • Dry & Dehumidify wet/damp areas - seal foundation cracks; repair air-conditioning condensate leaks; repair plumbing leaks; install and use a dehumidifier in damp areas.
    See What Indoor Humidity Level Should We Maintain -  
  • Basement de-watering systems: if all of my outside recommendations have been completed correctly (and have been verified as complete and correct) and then water entry recurs it may be necessary to install an  interior de-watering system.

    In general we do not recommend this approach as building dampness may still be excessive—it is more effective to prevent water entry from outside whenever possible.

    But sometimes outside measures are just impractical or more costly than an indoors basement or crawl space waterproofing project. Inside de-watering systems like B-Dri™ are a last resort. Basement waterproofing systems can be effective at keeping water off of the floors if they are properly installed.

    Improperly installed a basement de-watering system or basement waterproofing system and can create its own dampness problems in buildings. See Sump Pumps just below.
  • Suspect upholstered furniture, curtains - either try professional steam cleaning followed by HEPA vacuuming or dispose of this furniture;
  • Scented candles – can be a respiratory irritant to many people. We recommend abandoning use of and disposing of these items.
  • Sump pumps - and other crawl-space or basement de-watering systems must be absolutely reliable. Even a single-event flood in a basement or crawl space is likely to lead to costly cleaning and renovations all over again.
    See Buying, Installation & Maintenance Guide for Sump Pumps -

4.3 How to Dry Out a Problem Crawl Space

Crawl space venting – this is a debated topic as in humid weather venting outside air into a cool crawl space might increase crawl space moisture.

We no longer recommend simple passive venting nor humidistat-controlled venting except in special circumstances. When my inspection indicates a long-standing moisture problem in such an area the best current advice is to stop venting the crawl space(s)s and to convert it/them to a dry, conditioned space:

  • Provide a moisture barrier over any dirt floors and extending up foundation walls but not up to nor in contact with wood framing or sills. Moisture barriers may be 6-mil poly or other special basement sealer products such as special moisture-sealing concrete coatings
  • Be sure that the dirt floor moisture barrier slopes to a drain. A great many installations we see, even in company product literature, show multiple low spots in a crawl space, each of which is subject to ponding and water retention from leaks or other unanticipated water entry into a crawl space or basement.
  • Install a continuous dehumidification system (with a permanent drain hookup so the system can run unattended. Use an A/C condensate pump to a building drain if a gravity drain connection is not feasible.
  • A dehumidifier in a crawl space will also provide some heat in that area; if the crawl space is too cold (despite perimeter insulation) it may be necessary to add a small level of heat there. Some building also permit introduction of dry heat into these areas.

See our detailed article CRAWL SPACE DRYOUT - home for more complete information on how to dry out a wet or damp crawl space in order to reduce the chance of mold, insect damage, allergens, and structural rot.

5. Mechanical Systems Observations & Recommendations to Stop Indoor Thermal Tracking, Soot Stains, Ghosting

5.1. Heating, Cooling, Ventilation Systems

  • Heating equipment: For furnaces, obtain proper service, including proper filters (and/or improved efficiency filters), blower compartment cleaning including the compartment and the blower fan unit. See these references:
  • Central air conditioning: check the air handler(s) monthly (when the air filter is changed) to assure that the condensate handling system is not leaking into the building. If an attic system is missing a condensate overflow tray or missing a backup condensate overflow drain there is a risk of  leaks into the ceiling if condensate leaks occur in the regular condensate piping. See Air Filters for Heating and Air Conditioning Systems -
    and be sure to review the condensate leak issues
    at Condensate Handling -
  • Duct work: check further for mold or accumulated dirt, debris, dust, allergens; have professionally cleaned if the duct material can be cleaned. Light dust and debris in ducts is normal and does not normally justify professional cleaning. See Duct System Defects at

    If fiberglass board or flex-duct was used, flooded, contaminated (see lab report), visibly moldy or badly soiled duct sections will need to be replaced as these components can’t be cleaned and in my opinion encapsulants are unreliable. If non-cleanable replacement duct materials (fiberglass and flex duct) are installed they may need to be replaced again in the future.

    This may be cost-reasonable for accessible sections of flex duct but not for duct work run through building cavities or for major trunk lines. Watch out for incomplete-cleaning of duct-work; I often find mold growing where condensate collected in duct work is run through un-conditioned space such as a cool crawl space or hot attic.
  • Window and wall-mounted air conditioners: clean these units and replace or clean washable filters monthly during the in-use season. If mold appears inside the air path of these units they are probably not cleanable and will need to be replaced.

5.2. Plumbing & Other Systems or Equipment

  • Plumbing: Replace any corroded/leaky traps and where demolition exposes tub or shower traps assure those are sound before completing repairs. Watch for and repair any future plumbing leaks promptly.
  • Refrigerator: clean (using a HEPA vacuum) coils and grille as well as dust below and at other sides of the refrigerator. When cleaning the coil check that the evaporator tray is clean and that it is not spilling over. This is a common source of indoor mold and potentially Legionnaire’s disease.
  • Prevent future basement flooding: to reduce the risk of building flooding during severe storms and storm drain backup I have these related suggestions that you should consider:
    • Outside water: Repair and monitor possible outside sources of leaks and water entry I’ve already cited, as part of ongoing building maintenance and monitoring
    • Check valves: Install check valves in any basement or other low-level drains to assure that during severe weather and local flooding you do not have water entering the building through backing up sewers, septic system piping, or storm drains
    • Sump pumps: Install battery-backup sump pump system to assure that should water nonetheless appear in the basement level, it can be removed from the building during an emergency, even if electrical power is temporarily lost. See our Sump Pumps guide at m

6. General Notes on Sooting, Stains, and Mold Stain Prevention

Mold on drywall can not normally be cleaned sufficiently as portions of the mold growth are inside the gypsum and paper. Except in the case of trivial soil or mold on a painted drywall surface, replacement is the effective means of remediation for this material. Material removal is more reliable than simple surface disinfection, but steps must be taken to avoid contaminating the building with construction dust and mold spores.

Check/remove baseboard trim at floors: where floors or wall cavities have been flooded I often find mold growth on the back of baseboard or door trim, and on either or both sides of drywall or plaster where trim was installed; don’t assume that there is no mold in a wall cavity or that there is no mold behind wood trim just because no mold is visible on the wall surface.

Avoid mold growth: Reduce or eliminate the conditions that encourage mold and fungal growth. In any building where there is recurrent water entry, there is risk of the conditions which produce or amplify mold growth.

General moisture control: keep un-wanted water and moisture from entering the building from outside (maintain roof drainage system to avoid spillage at the foundation, slope grade away from the building, provide flashing and sealant at openings), avoid generating unwanted moisture inside (unattended plumbing leaks, missing venting, un-covered dirt crawl spaces, open stone foundations), and remove unwanted high-levels of moisture inside (dehumidification, ventilation, drainage)

Depending on species, mold spores may die or become dormant, failing to reproduce, at low moisture levels. If the building is sufficiently damp or wet again, mold growth will probably recur.

Always identify and correct obvious outside sources of water entry before going to the expense of costly basement waterproofing systems, though in some cases such systems may be necessary.

Install a high-capacity dehumidifier and run it until basement moisture is in the 45-55% range. You may want to purchase an inexpensive relative-humidity indicator for this purpose. (See Radio Shack products.) You can drain the dehumidifier by a condensate pump or to a sump pit so it can run unattended (except for periodic cleaning).

Missing backup condensate drain – can be compensated-for by installing a leak detection system in the condensate tray. This design will shut down the A/C system if a leak is detected, preventing water damage to the building from this source.

Reader Question: Is there a professional whom we can contact for help in curing thermal tracking stains?

First of all, I want to say thank you! Your site is the ONLY site that I was able to find the answer to what is wrong with my house. I now know that I have Thermal Tracking. My question to you is: Is there a professional that I can contact to take care of this problem? What type of person would do that? My home is 12 years old and we’ve been dealing with this every since we bought it. We did not build it, but purchased it from a couple that had lived here for only one year. Thank you for your help! - Cindy

Reply: Yes: home inspectors, energy consultants, experienced insulation contractors

Sure, here is a concise recap of our advice on curing thermal tracking stains (What is Thermal Tracking) in buildings: (see details above in this article)

Thermal tracking stains are essentially the combination of these factors:

  1. Missing, incomplete, or inadequate insulation in walls or ceilings (See INSULATION INSPECTION & IMPROVEMENT)
  2. Interior moisture levels that produce condensate on cooler sections of walls or ceilings (see HUMIDITY LEVEL TARGET)
  3. Level of indoor house dust or soot
  4. Drafts that move extra air across some surfaces can also be a factor in thermal tracking stain location. (See AIR LEAK DETECTION TOOLS)

Simple cleaning and painting will of course remove or cover the stains from thermal tracking. But unless the cause of these stains is corrected as well, they will return.

The optimum "fix" for these indoor stains on walls and ceilings and even sometimes on floors or carpets near walls (Floor Carpet Thermal Tracking Stains) is to improve building insulation, but of course that's the most costly step too, but then again, improving insulation returns savings in lower heating or cooling costs for the building as well as increased comfort.

Short of improving insulation you can find and fix sources of excessive indoor moisture, stop using scented candles or other indoor burning things that produce soot, and improve housekeeping (better, HEPA-rated vacuum cleaner, for example) so that the level of house dust is reduced. And of course find and fix air leaks and drafts. An experienced home inspector or energy auditor (EXPERT DIRECTORY) should be able to help you track down and prioritize the locations and causes of the four thermal tracking stain factors I listed above.

Reader question: trouble painting over stains: keep bleeding through

(June 29, 2014) Colleen said:

I have used primer to cover thermal tracking marks on wall studs and ceiling joists on interior walls only to have them reappear. What should I do to remedy the problem? Black marks, which follow studs and ceiling joist only on the sheetrocked exterior walls, continue to show through primed and painted walls. There have never been any improperly burning heaters, wood-burning stoves, non-vented heating appliances...used in the home. Interior walls are not affected.

Reply: use a lacquer primer sealer when painting over black stains on interior walls

Colleen, the reappearance of stains through some paints is a common and annoying problem. Usually the root problem is that the stain is bleeding through a water soluble paint or on occasion even through an alkyd paint or primer.

Try a lacquer primer sealer such as "Bin" or "Enamelac" or if those are not handy, spray the stains with a coating of spray shellac - clear or white if you prefer. When that's dry you should be able to paint over with your primer and not see the bleed-through.

Thermal tracking marks will of course recur if we don't also address it root causes: indoor dust or debris levels, moisture, uneven or missing insulation.

Reader follow-up:

I have taken up all carpet and floor coverings to replace with hardwood, had all ductwork cleaned and will continue to monitor indoor moisture and dust levels. Hopefully this is the last time I have to prime all interior walls and ceilings before painting. Ceilings are equally as affected by the streaking/sooting effect.

Do you know of any issue related to having two layers of vapor barrier inside walls contributing to this problem? The house was built in 1976 and is very well insulated, but side walls have foil-coated insulation batting between the studs and plastic on top of that, next to the sheetrock. One contractor suggested that may be contributing to the problem, saying a home should have one or the other but not both. The ceilings, however, have only plastic for a vapor barrier and are still equally as stained as the walls. It seems to make sense to me that the root cause would be related to dust/debris, moisture... that you suggested, versus an improper vapor barrier. Your thoughts?



Indeed we don't want to create a vapor-barrier "sandwich" with insulation between;

In a heating climate the vapor barrier goes on the warm side of the wall - the interior surface of the wall studs over which drywall is installed.

In a cooling climate the vapor barrier goes on the warm side of the wall too but that becomes the exterior surface of the wall.

If you are seeing sooting streaks read about THERMAL TRACKING BRIDGING GHOSTING at



Continue reading at INDOOR HOUSE DUST & DEBRIS or select a topic from the More Reading links shown below.



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THERMAL TRACKING REMEDIES at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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