Carpet Filtration Soiling

By Doyle Bloss / Marketing & Brand Mgr. at HydraMaster & U.S. Products
Published in Cleanfax Magazine /
December 05, 2013

Filtration soiling is a carpet care problem many cleaning technicians encounter in both commercial and residential settings.

Filtration soiling is a term used to describe dark, gray (sometimes black) lines that can appear on carpet as it acts as a filter to dust and other airborne pollutants. It accumulates on carpet fibers in areas with a concentrated flow of air over the carpet. It can also develop as a result of tiny cracks or other open areas in the subfloor under the carpet.

Filtration soiling is most commonly found around baseboards, under doors, along the edges of stairs, near HVAC vents and in areas where plywood subflooring

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materials have been joined. Such soiling can also be the result of fireplace emissions and can even come from cooking oils that have become airborne and settled into the carpet, a problem that often occurs in restaurants. It can be the result of the use of candles in homes.


This issue is not a carpet defect, nor is it a result of the quality of carpet selected. However, the condition will obviously appear more pronounced on lighter colored carpet fibers as compared to darker ones.

Very challenging to remove, filtration soiling often develops over a period of months or even years; however, it can also develop fairly quickly. The level of soiling can vary, and is typically dependent upon the volume of airflow and the level of pollutants in the air. In residential settings, concentrated airflow moving from an upper level to a lower level can also cause filtration soiling to occur.

Removing filtration soiling

One of the challenges of removing filtration soiling from carpet is that these soils can be very fine and contain a combination of water-soluble and solvent-soluble solids

This means that, in some cases, different cleaning treatments or a combination of cleaning treatments may be needed to achieve complete removal.

Additionally, while there are several specialized filtration soil removers now available that may work well to remove the soil, at least temporarily, some products can leave behind a sticky residue that can result in rapid resoiling. You must do your research.

Some chemicals, gels, and even chemicals that use citrus solvents are now available that are effective at removing filtration soiling without leaving a sticky residue. An astute distributor should be familiar with filtration soiling and, in many cases, will be aware of the products that, when used properly, have proven to work well.

Working with these products, the following steps should be taken:

  • Thoroughly vacuum the area before cleaning.
  • Always pre-test the product in an inconspicuous area for colorfastness prior to application.
  • To protect the wall or baseboard, use a “shim” of some kind. This can be a piece of wood, plastic or cardboard that will protect the wall or baseboard from cleaning chemicals.
  • Dilute the chemical treatment per the manufacturer’s instructions before use. Many cleaning professionals select a trigger sprayer, flip-top spotting bottle or hand-held pump-up sprayer for application. Avoid over spraying or inhaling the product mist.
  • Once the chemical has been sprayed or applied to the affected area, allow it to “dwell” on the carpet for a few minutes; next, carefully agitate the area to work the solution into the carpet.
  • Extract the treated area using a hot-water extractor with an acid/neutralizing rinse; the hotter the water, the better the results will be (as long as the temperature is safe for the carpet fiber).
  • For faster drying, especially in humid environments, consider using an axial, centrifugal or downdraft air mover after cleaning.

Filtration soiling often becomes an ongoing problem, and not surprisingly, often appears repeatedly in the same areas. According to the Carpet and Rug Institute, there are several ways to prevent, or at least slow down, filtration soiling:

  • Apply soil- and stain-resistant treatments to the affected area.
  • If the problem is caused by airflow from HVAC vents, install high-efficiency air filters and change them regularly.
  • If air is coming from under doors or walls, properly sealing these areas can help address the problem.
  • In residential settings, technicians should advise customers that cigarette and cigar smoke can contribute to filtration soiling.

Filtration soiling is a relatively common problem in both residential and commercial settings that most technicians will have to address from time to time.

Fortunately, using the appropriate treatments and chemicals, filtration soiling is treatable, and can even be prevented when proper steps are taken.

R. Doyle Bloss has been a part of the cleaning and restoration industry for more than 30 years. He presently serves as the marketing and chemical brand manager for HydraMaster and U.S. Products in Mukilteo, WA. He has headed up the two largest training programs in the industry, assisted in developing complete chemical lines for three leading manufacturers and has been honored and awarded for his innovative programs that build bridges throughout the cleaning and restoration industry. He may be reached through his company website at