Carpet Cleaning Tips

How to Clean the Dirty Edges of a Carpet and Prevent Filtration Soiling

The draught marks on carpet and rugs are caused by what is known as filtration soiling and are mostly visible along the edges of the affected item. At first, you might think that you are dealing with some sort of mildew but this is not exactly what is going on.

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So, if you:

  • Wonder why the edges of your carpet get dirty;
  • Want to know how to clean them;
  • Are looking for ways to prevent it from happening again,

Keep reading! This article will answer your questions.

These greyish dark lines on carpets are most visible around the baseboards, near air vents and doors, or along the edges of stairs. This suggests that the issue at hand has something to do with the ventilation of the room. Thankfully, a carpet cleaning may bring back the aesthetics of your rug but you still need to check your home ventilation system to prevent those filtration lines from reoccurring.

Here we will explain exactly what causes the dark spots and share with you how to effectively clean the dirty carpet edges.

How to clean the dirty edges of a carpet

Time needed: 2 hours.

These spots are actually quite difficult to remove and vacuum cleaning alone won’t do the trick. The dirt has settled deep between the fibres and it needs to be dislodged with water and forceful scrubbing. Here is how to deep clean the dirty carpet edges:

  1. Agitate the pile of carpet with a hard-bristle brush or a pull scraper.

  2. Place the crevice tool on your vacuum cleaner hose and run it along the affected area.

  3. Dip a clean white rag in warm water and vigorously scrub the black marks on the carpet.

  4. If the spots are still there, then you’ll have to resort to some detergent.

  5. You can get a commercial carpet shampoo from a local store or prepare your own solution of mixing white vinegar, lukewarm water and a bit of liquid soap.

  6. Apply your chosen cleaning solution on the remaining dark spots of your carpet and scrub them away with a hard brush.

  7. Use wet white rags to wipe away the foam and loosened dirt.

  8. Let the textile floor covering dry, then vacuum once more to remove surface dirt and any loosened fibres.

If you prefer to sanitize the whole carpet and not just around the area around baseboards, make sure you are cleaning it the right way. If in doubt, click here to read our post on the most effective carpet cleaning methods. There you will find a definition of each method and the pros and cons of each technique as well.

Here is what causes the black lines at the edge of your carpet

The issue is known as filtration soiling, a problem that comes from an imbalance in the ventilation of the space.

The rate at which air leaves the room is lower than the rate of which it enters. When this happens, some of the escaping airflow is forced to go through the available alternative routes such as the small spaces under closed doors and between floor boards. When the air passes through the carpeting, it is being filtered by the fabric. The piece begins to accumulate pollutants and the black marks become visible with time.

What are filtration soils?

Here is a quote from Carpet & Rug Institute:

Filtration soils may be fireplace or automobile emissions, residue from furniture polishes, fine sand or clay particles, cooking oils, or a host of other soils. Oily airborne contaminants trapped by carpet fibers will serve to attract more dry soils.

You can find their technical bulletin on the subject of carpet filtration soiling here.

How to prevent filtration soiling in a carpeted room

The tactics for keeping these black lines on your carpet from coming back range from free to generally cheap and should be easy to incorporate within your household or place of business. Follow the steps below to prevent or at least reduce the filtration soiling of your carpets:

  • Reduce air pollutants. Eliminate any factors that contribute to the pollution of the air in the space. These are processes that include a form of burning, combustion, evaporation, and/or dispersion. The most common examples are indoor smoking, cooking, humidifiers, and the usage of air fresheners. If all of these are present, consider increasing the cleaning frequency of your carpet.
  • Minimise dust accumulation. Remove (or at least reduce) items from the room made out of cloth and other fabrics that shed particles. These might include fabric curtains, lace doilies, plush toys, and a wide variety of upholstered items.
  • Ease the ventilation. Keep the door/s of the room widely open as much as possible throughout the day. If possible, air out space by opening the windows occasionally. This will even out the indoor temperature a little bit which is also helpful.
  • Block the gaps. Identify the air escape routes in the room that contribute to the problem and block them as tight as possible. For example, the space between the baseboard trim and the carpeting can be filled with an expandable foam sealant.
  • Clean the ducts. With time, air ducts accumulate serious amounts of dust and other unsanitary agents that affect the quality of indoor air. Therefore, have your ducts inspected and cleaned thoroughly on a regular basis that meets the needs of your living space or commercial facility.

Need more advice on how to keep your textile floor covering clean? Then why not check out our post on the topic. It’ll show you how to clean a carpet, including how to vacuum properly and how to lift stains with ease.

Our deep carpeting cleaning also does the trick

If you have the time and are willing to put in the manual work, then you can solve this problem on your own. But keep in mind that we can lend you a helping hand, especially if it’s high time to give your carpeting a comprehensive wash. We perform professional hot water extraction which is the best and most efficient way to clean dirty carpet edges. Hot water extraction, commonly known as steam cleaning, quickly dissolves the accumulated grime and removes it almost immediately along with 95% of the moisture. In addition, we can treat your carpets and rugs with stain protection product to prolong the result.

Learn what carpet cleaning solutions we offer here!

Please note that you need to solve the ventilation problem of the room. Otherwise, the dark spots will appear once again.


  • Dark dirt marks around the edges of your carpet are caused by an issue called filtration soiling.
  • Filtration soiling occurs when there is an imbalance in the air ventilation of the room.
  • To clean up these stains, you need water and vigorous scrubbing.
  • You may need to use detergent for more persistent stains.
  • Prevent this from occurring by reducing air pollutants, minimising dust accumulation and fixing any ventilation issues.


Okay, now you know what causes these dark lines on your carpet’s edges. Has this guide been helpful to you? Let us know in the comment section!

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