Filtration soil may appear as dark or grayish lines on carpet along walls, stairways and under doors. It is caused by airflow over and through carpet, allowing fine soils to settle on the surface. This is often caused by an improperly balanced ventilation system, when the volume of air entering a room exceeds the system’s capacity to remove air from the room. Excess air then seeks exit sources in gaps along walls and stairways.
The soils in the air that actually cause the filtration lines can be a host of different soils, but are most commonly cooking oils, soot from burning candles, poorly ventilated fireplaces, fine sand & clay particles, and many other indoor air pollutants. Although routine vacuuming will help slow the build up, these microscopic particles are so fine they easily bond to and penetrate carpet fibers making them difficult to remove even for professional carpet cleaners.