Filtration Soil: What It Is and How to Get Rid of It

Cleaning and preventing dark edges on your carpet

Person using a steam cleaner to clean carpets.

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Are you wondering why your carpet is turning black at the edges? Those carpet lines are caused by something called filtration soil.

What Is Filtration Soil?

Filtration soil is an accumulation of household contaminants, such as dust, pet hair, smoke (especially from burning candles), fireplace ash, cooking oils, and outdoor pollutants that get caught in your carpet's fibers and appear as black or gray areas, lines, or streaks. In most cases, filtration soiling is not mold.

Filtration soil can also occur as black lines forming on your carpet along the walls, under doors, around air vents, or along the edges of your stairs. Read on to find out what causes filtration lines in carpet, how to clean carpet edges, and how to best remove those lines, if it's possible.

What Causes Black Lines Along the Edge of Your Carpet?

Filtration soiling occurs as a result of air being forced into the room or space at a higher rate than it can escape from the same area through the ventilation system. The air then seeks alternative escape routes, which usually end up being the gap between the carpet and the wall trim and under closed doors.

As the air is forced through these gaps, it passes over the carpet, which acts as a filter for the air. Any pollutants in the air are trapped by the fibers and over time the carpet turns gray or black in that area.

This soiling does not occur as a result of insufficient vacuuming or improper vacuuming techniques (although consistently failing to vacuum the very edge of the room can help to amplify the problem). It is a problem that can occur in the cleanest of homes and is not considered a reflection of housekeeping abilities.

How Do You Clean Soil Filtration?

Discoloration of the carpet caused by filtration soiling is very difficult to remove. The particles are extremely fine so they end up firmly embedded in the fibers of the carpet. In some extreme cases, it may not be possible to fully remove all traces of the soiling.

There is no readily available or reliable carpet filtration soil remover product available to purchase unless you are a commercial carpet cleaner. For this type of soiling, it is best to let the professionals handle it. Contact your local carpet cleaning company, explain the situation, and ask for some advice. The cleaning method that is likely to be most successful as a filtration soil remover is hot water extraction (commonly known as steam cleaning). A cleaning solution added to the water in the machine will help in removing much of the soil filtration lines.

How Can Soil Filtration Be Prevented?

There are steps you can take to minimize filtration soiling from developing. Once it has occurred, however, it is difficult and sometimes costly to remove. Here are several preventative measures that can reduce the formation of soil filtration lines.

Start With the HVAC System

The first step to preventing filtration soiling is to have your home's ducts cleaned. As the air is forced through the ventilation system, it picks up whatever dirt is in the ducts, and carries it into the home and potentially into the carpet. Experts advise that having your ducts cleaned regularly is one of the best ways of preventing this soiling in your carpet.

Additionally, be sure to change your HVAC (furnace/air conditioner) filter regularly, as recommended by the type of filter you use (some last longer than others). The filter traps a good portion of airborne pollutants, preventing them from traveling through the duct system and out into the main areas of the home.

Eliminate Gaps

Another way to reduce the problem is to eliminate the gaps through which the air seeks to escape. As much as possible, keep interior doors between rooms open to allow the air to move freely through the opening so that it does not travel down and into the carpet as it tries to escape under the closed door.

Gaps between the carpet and baseboard trim may be sealed using an expandable foam sealant. Depending on the size of the gap, you may need to pull the carpet away from the wall to access the entire area and avoid getting any of the sealants on the carpet. The carpet would then have to be re-installed over the tack strips using a stretcher or a knee kicker.

Reduce Pollutants

Finally, some lifestyle changes may assist in the reduction of the problem. Avoid smoking inside the home, and reduce or avoid the burning of candles in the home. (If you enjoy the ambiance and aroma of candles, try using battery-operated flameless candles or using an electric warmer to heat the fragrant wax.) Ensure that your home is as dust-free as possible with frequent vacuuming and thorough dusting. Always cook with your stove's hood vent fan running to remove smoke from your home.

Install Darker Carpet

It goes without saying that lighter-colored carpets will show the problem to a much greater extent than dark carpets. If you find that, despite your best efforts, the problem continues to occur, you may opt to replace your carpet with a darker color to mask the issue and give yourself some peace of mind.