Do you have UNSIGHTLY Black Lines around Carpet Edges, Baseboards and Under Doorways?

By John Alderson

Do you have UNSIGHTLY Black Lines around Carpet Edges, Baseboards, Under Doorways and Near HVAC Returns?

Most homes have some of this mystery black stuff somewhere on the carpet and it’s one of the most popular questions that I get asked about. “What is it and what causes it?”  Mainly homes that have carpet with lighter shades of carpet or white carpet will see it starting to just come out on nowhere. You may have also noticed it mysteriously forming around baseboards in the perimeter of rooms, hallways and under doorways.

This type of soiling is called Filtration Soiling and you may have heard that that cannot be removed – Not so True!!!

Filtration Soiling can be usually found in heavier concentrations around the HVAC returns, 2nd story of a home and above floors. Homes built on craw spaces can have Filtration on the first floor too. It can also form around A/C vents in the carpet.  In some severe cases it can extend out over a foot from walls. Filtration soil can even occur in the center of rooms where floor boards meet.

Filtration Soiling main culprit is the HVAC system drawing air from the living air space(in rooms) and pulling  through the carpet edge where it meets the baseboard. Just behind the baseboards and sheet rock where the framing of the house meets is a gap where the air passes threw inside the wall.

Filtration Soil is formed from the carpet filtering fine dust, pollution, pollen, ash from fire places, candles, soil, gas heat, burning food on the oven and everything that is found in your indoor air environment.  The same soil that is composed in your A/C filter is the same soil in Filtration Soil.    The soils are filtered onto the carpet as the air passes through threw below the walls and under doorways creating the dark lines.

This airflow flows inside the wall cavity and eventually leads to the HVAC system.  Improper sealing or not enough sealing at the connection points of the HVAC can create this draw of air along the edges of carpet. The home itself may have not been properly insulated and indoor air or even outdoor air can freely flow out, or in the home.

Attempting to permanently prevent Filtration Soil from occurring is a difficult process and may not really worth the time and effort required to stop if from reoccurring.

 Here are a few tips to help with the problem.  

  1. Sealing the duct system by finding the leaks and sealing them with HVAC Duct Tape. All systems have a lot of small holes and leaks especially near junction boxes where ducting comes into the box and the boxes themselves.  This may not eliminate the problem but may reduce the reformation time of the Filtration Soil.
  2. Removing all the carpet around the areas where the Filtration soil has formed and caulking where the gap where sheet rock and the framing. Then reinstall the carpet. This may cause the air to pull from other locations where you did not seal. You can also install wood floors or tile.
  3. Vacuum with a crevice tool and wipe with a damp white terry cloth. Watch out for the tack stripping just below on the edge of the carpeting, it can cut fingers and be very painful!
  4. Changing your HVAC filters in a timely fashion. Most only last 1-3 months. The more heavily soiled they get the more HVAC system draws from the holes in the system.   
  5. Professional Carpet Cleaning every 6-12 months can help keep filtration soil from occurring and building up.

Filtration soiling is extremely difficult to remove because the particles are very fine and they can deeply embed into the carpet fibers, pile and into the backing of the carpet.

Good News!!!! Universal Cleaning Services can remove even the most severe Filtration Soiling with our special cleaning system for Filtration Soil. Call us today to schedule an appointment.

{ 7 comments… read them below or add one }

golfgpsgolfgpsreviewselectronicsbestgolf March 16, 2013 at 1:07 am

I was looking at some of your content on this site and I believe this internet site is rattling instructive! Keep posting.


michelle thomas July 24, 2013 at 2:20 pm

I am interested in carpet cleaning to remove Filitration soiling!


John Alderson September 17, 2013 at 3:02 pm

By: John Alderson

Please call our office at 919-602-5592 so we can help you remove the Filtration.

We offer a Free no obligation carpet audit which is a complete thorough inspection of your carpets current condition. During the audit we can address any stain concerns, odor problems and can identify the carpet type. No high pressure sales pitch either!



Sally September 12, 2013 at 1:46 pm

I have a new (3 month) cream loop stair carpet on 3 flights of stairs and 3 landings.  A black mark has appeared on each nosing in the middle of every step.  It is not across the entire nosing just the middle and not anywhere on the landings.  The manufacture sent an inspector round and he said it was caused by draft as we have parquet flooring in the hall.  My supplier says he will come back seal each stair, put paper under the underlay and clean the carpet.  Will this work?  The previous stair carpet was mid blue and was down for 15 years without any marks coming through.


John Alderson September 17, 2013 at 2:57 pm

By: John Alderson

Yes, this is caused by the air flowing threw the carpet and into a gap in the subflooring. The carpet is filtering out the air and leaving a carbon deposit in the carpet fibers.  I would use plastic NOT paper as the liner because if the paper tears or gets a hole in any area you could have the filtration soil form in the torn areas. Do not use staples or nails to attach the plastic – if you have too make sure you seal the holes up.  

Do you have an A/C return below the stair case?  This could be the cause because the draw on the unit.  Filtration soil will not usually show on darker shades of carpets or be noticeable to the eye.  Some other causes could be from outdoor pollution, candles, smoking or a drafty house with a lot of outdoor air working its way into the home. If you need any further help please let me know.



john huber July 11, 2014 at 6:02 am


Cincinnati carpet cleaners have tried but apparently don't know how to remove this stuff.

What do you use, and how do you use it?



I Love carpets September 18, 2014 at 8:04 am

It is actually a nice and helpful piece of information. I’m
satisfied that you just shared this helpful information with us.

Please keep us up to date like this. Thank you for sharing.


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