Have
you ever noticed a grayish or dark line along the walls on your carpets?
You probably do not want to know this, but it is not a
defect in your carpet. It is called soil filtration and is a concentration of
dirt that has collected on the carpet fibers.
Soil Filtration is caused by positive and negative pressure
within a building. What happens is, when pressure change occurs within a room
from either the effect of warm air rising or from mechanical pressures, air
tries to flow either in or out of the room. The carpet along the wall edges
serve as a filter as the air exits or enters under pressure.
Have you ever noticed a grayish or dark line at the doorway
of a room? Once again, soil filtration. It is quite common for dirt and dust to
accumulate under doors when they are shut. The supply air vent blowing air into the room creates
positive pressure in the closed room. This air will seek areas of lower
pressure (the return air vents) through the largest available holes. With the
door shut, the undercut of the door is generally the largest available hole.
Therefore, as the air passes between the door undercut and the carpeting, the
carpet acts like a filter taking out dirt and dust particles from the air. Over
a period of time, the carpet will darken as the dirt accumulates.
Because soil filtration is a concentration of dirt
particles, cleaning soil filtration areas can be very difficult.
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