Carpet Cleaning Filtration lines Franklin Michigan

When I was doing a carpet audit in Franklin Mi. I came across a client with dark lines that ran parallel to the wall about one inch away. This is known as filtration soiling or soil filtration lines.What are soil filtration lines? Soil filtration lines are ugly dark lines – usually from 1 to 3 inches in width –  that often show up in homes along the baseboards, under doors, along stairways, around furnace vents and under floor length draperies. Removing dark lines on carpeting can be difficult.

The Cause

Filtration soiling is caused by smog, soot, dust, carbon monoxide and other microscopic airborne pollutants that pass through the carpet pile. As the pollutants pass through the carpet, the fibers act as a filter to remove the fine particles of airborne soil. The pollutants build up in the carpet and slowly turn from light gray to black. Homes and businesses in the vicinity of large cities, industrial areas or near busy roads and highways are more prone to filtration soiling, because of increased levels of air pollution, although no building is immune.

The pollution enters the home via foot traffic, through open doors and windows, from “fresh air” intakes on heating and cooling systems, or from the crawlspace.

Airborne pollutants are distributed throughout a building via the heating or air conditioning system or through natural convection currents in the building structure. In virtually every home and building, gaps are found at the lower edge of walls, between steps and the walls of a staircase and between the floor and the drywall. Soil filtration lines may take weeks, months or even years to appear.

Ironically, newer, more energy efficient homes are more likely to have soil filtration lines than older homes, because the exterior walls are usually more air-tight, forcing more air movement through gaps in the interior walls.  The popularity of lighter colored carpets in newer homes has drawn attention to the problem, since light colors show soil more readily.

Olefin and polyester carpet fibers show the greatest affinity to filtration soiling. This is due to the oily nature of the pollutants and the oil-loving characteristics displayed by these fibers. This chemical attraction can cause a reaction whereby the oily deposits become a part of the carpet fiber, making them very hard to remove. Nylon fibers are somewhat easier to clean because they do not have as strong a chemical infinity to filtration lines.



It is very difficult to completely prevent soil filtration lines. Sealing cracks along a wall with caulking or expanding aerosol foam insulation will help, but may force it to occur somewhere else. The best method of prevention is to develop a habit of vacuuming along baseboards and stairways weekly, using a crevice tool. Also, during the months of heaviest usage for your heating or air conditioning system, change the filters at least monthly. Clean filters pull more airborne pollutants from the air, cutting down on the amount of pollution that can be passed through the carpeting.



The longer the problem goes untreated, the more difficult it is to correct. Once the lines become charcoal or black in color, an improvement is about all one can hope for. Due to the oily nature of filtration soil, once the problem has reached this stage, a professional carpet cleaner needs to be called in. It takes a professional carpet cleaner that has an education and certification in carpet cleaning to get this very difficult problem resolved.  Carpet cleaning spot removers may help in the short term but will leave a detergent and solvent residue behind that will make the problem worse in the long run.

As always, if you have any questions about this subject, please feel free to call our office!