Filtration Lines

Filtration soiling is a term used to describe dark, grayish lines that may appear on carpet. This is not a carpet defect, but a situation in which dust, smog, and other airborne pollutants can accumulate on the carpet face fibers in areas with a concentrated flow of air over the carpet or through tiny cracks or other open areas under the carpet. The soiling condition can occur quickly or it may develop over a period of months or years.  The level of soiling is dependent upon the volume of air flow and the level of pollutants in the air. Filtration soiling is not dependent on the quality of carpet selected. The condition will obviously appear more pronounced on lighter colorations than darker color tones.

Filtration soiling areas may appear around baseboards, under doors, along the edges of stairs and possibly away from walls where plywood subflooring materials have been joined.  Generally, the concentrated air flow will be from an upper level to a lower level of the home.

As indicated, filtration soiling can occur under closed interior doors where a central heating, ventilation, and air condition (HVAC) system is utilized. Interior doors should remain

open to reduce filtration soiling that may develop

under closed doors while the HVAC system is in operation.

Filtration soils may be fireplace or automobile emissions, residue from furniture polishes, fine sand or clay particles, cooking oils, or a host of other soils.  Oily airborne contaminants trapped by carpet fibers will serve to attract more dry soils.

It is difficult to identify effective methods to reduce or prevent filtration soiling. Preventing airflow through carpet and carpet edges by sealing cracks in the subfloor, as well as under baseboards and edges of stairs may reduce filtration soiling problems.

Keeping air inside the home as clean as possible can be accomplished by reducing indoor pollutants such as cigarette smoke and cleaning chemicals; by the installation and regular replacement of high efficiency HVAC air filters, and by use of high efficiency vacuum cleaner bags.

While no one cleaning technique may be successful in all filtration soiling situations, recent innovations in soil and stain resist treatments applied to carpet have reduced the effort previously needed to remove the filtration soil.  However, the

complete removal of contaminants from the soiled areas can be complicated depending  on the type of contaminant materials present.  Therefore, the services of a Seal of Approval (SOA) Service Provider should be considered to achieve the best results.  To locate an SOA Service Provider, go to the Carpet and Rug Institute’s website at

CRI Technical Bulletin:  Filtration Soiling 0314

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