 Dark,
grey or brown lines under doors, around walls, underneath draperies
and along the edges of stairs are symptoms of an aggravating problem
called filtration soiling. This article explains the cause of this
problem and suggests effective methods of prevention and correction.
The removal of filtration soiling will not be successful with normal
carpet cleaning procedures. The removal of filtration soiling is a
separate process which can take up to 40 minutes per room.
Filtration soil removal is a time consuming and sometimes expensive
exercise and you need to consider the cost of filtration soil
removal to carpet replacement.
 What
is Filtration Soiling?
Filtration
soiling is the accumulation of airborne soil—dust, smog, tobacco
smoke and other pollutants—where airflow is concentrated and
directed over or through a carpet’s pile. The carpet “filters” out
these pollutants and gradually becomes soiled and dark. The most
common area you see filtration soil is around and close to walls.
Filtration soil is more evident on white or cream coloured carpet.
In addition to the areas shown in the accompanying photographs,
filtration soiling
 can
occur anywhere air flows over or through the pile, including places
where the carpet’s back has been punctured or torn by installation
tools, along seams that abut baseboards, around railings on stairs,
and other areas. You may even find it around the holes created in
carpet’s backings by the pins of tackless strip. In these cases, the
path taken by the air differs, but the cause of the problem is the
same.
Filtration soiling may appear over a period of only weeks, or it may
take months or even years to become visible. The severity of the
soiling will be proportional to the volume of airflow and the
relative dirtiness of the air. Its colour will vary according to the
type of contaminants present. Auto emissions are grey to black;
tobacco smoke is tan to brown (and easier to remove by cleaning).
It is most visible
on carpet of lighter colours, such as off-whites, light greys,
beiges and pastels.
Is the Carpet
Defective?
No. Filtration soiling is not the result of any defect in the carpet
or its components, nor is it an indication of low quality. It can
appear on any carpet regardless of price, style, colour,
construction or face fiber. Since it is caused by airborne
pollutants being deposited on the carpet after it is installed,
filtration soil is not affected by anything done when a carpet or
its pile fibers are manufactured. While fluorochemical soil
retardants (e.g., Scotchgard, Teflon, etc.) may make it somewhat
easier to remove, no fiber modification or protective finish can
prevent filtration soiling from occurring.
What Causes the
Airflow?
In most cases, the airflow is created by heating and air
conditioning systems, thermal expansion and contraction of air, or
natural convection currents in the structure. It also may be caused
by wind blowing through windows that regularly remain open.
Can it Be Prevented?
Leaving inside doors open as much as possible will help prevent
filtration soil from accumulating in doorways. In other areas the
airflow itself must be stopped. Along walls and staircases, the
carpet will need to be disengaged and the gaps through which air
flows must be completely sealed off. (Silicone caulking and
polyurethane foam insulation are ideal for this purpose.) However,
if any gaps remain, air will find them. Sealing off some gaps may
simply force air to find another route—possibly through the carpet
in another area.
Can It Be Corrected?
Usually filtration soil is at least partially correctable by a
professional cleaner; however, it rarely responds completely to
routine cleaning. Filtration soil consists primarily of extremely
fine particles—much smaller than soil from other sources—which can
be very difficult to remove. It is thought that because of their
small size, the particles are held stubbornly to the fiber's and are
not easily removed in the normal carpet cleaning process. Some
components of filtration soil—auto emissions, for example—are oily
in nature and have an affinity for synthetic carpet fibers. These
factors, combined with the fact that the soil typically remains on
the fibers for months or years, make filtration soil highly
resistant to ordinary cleaning. Natural fibers like wool cannot
tolerate the chemically aggressive cleaning techniques usually
required to remove filtration soil.
The largest case (by dollar value) I ever worked on was a lawsuit
against a construction company, who was blamed for severe airflow
problems, which caused extreme filtration soiling. As (bad) luck
would have it, nearly all of the units had white or beige carpet
with nylon or polyester pile. By conducting extensive cleanability
testing, I came up with a four-step procedure which successfully
removed 90-100% of even the most severely affected areas:
1. Pre-spray the affected areas with Ramsey’s Pre Oil Break diluted
1:1 with hot water. Agitate the pile gently with a dry, white
terry–cloth towel. (A cotton towel has a lot more surface area than
bristled brushes.) Allow to dwell for 10 to 15 minutes.
2. Thoroughly extract the pile with a 1% solution of ProChem’s
Emulsifier Plus extraction detergent. (Note: A defoamer will be
needed in the extractor’s recovery tank when extracting Pre Oil
Break.)
3. Pre-spray the affected pile again using ProChem’s Ultrapac
Renovate diluted 16:1 with hot water. Agitate the pile gently with a
dry, white terry–cloth towel. Allow to dwell for 10 to 15 minutes.
4. Thoroughly extract the pile again.
Repeat these steps until it stops responding or, more likely, it’s
all gone. Note that these agents may damage paint and wood finishes,
and some weakening of the carpet’s lamination may occur, at least
while the carpet is wet. (That’s nothing a little latex won’t fix.)
 As
you can see filtration soil removal is a time consuming and
sometimes expensive exercise and you need to consider the cost of
removal to carpet replacement.
If you’re going to the trouble of disengaging the carpet to seal off
areas where air flows, you might not have to worry about cleaning at
all. You can take advantage of the reinstallation to restretch the
carpet (using a power stretcher, of course) and physically trim off
the soiled edges. If the airflow is completely stopped, then the
problem is permanently solved.
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