Draught staining on carpets 

Draught lines on carpet

What is draught staining on carpets? 

Draught staining  on carpets, also known as filtration marks, is a permanent, dark staining near skirting boards, air ducts, under doorways and in other areas where moving air may filter through carpet fibres.

Draught staining is a common problem in the UK, with many home owners finding that this type of staining, which is caused by carbon soot, is extremely difficult to remove.

Where does it happen? 

Soot deposits are usually seen in homes that are constructed using floorboards for the flooring, but soot stains can also be found in particle board floored homes as well and can be quite common in newly built residences. 

What causes soot staining?

Dust or dirt causes most of the marks on a carpet, and our deep cleaning machines will wash them out quite easily. But staining caused by carbon soot, which can come from inside or outside the house,   often permanently marks the carpet. This type of soot staining cannot be removed using a regular vacuum cleaner or household type carpet cleaning machines.

The main factors that cause this type of soot staining is a source of carbon soot, coupled with air movement, causing carbon particles to move through the carpet which acts like a filter.

Carbon soot sources

Carbon soot is particulate matter — it is made up of very small particles.

Research shows that houses in close proximity to exhaust fumes from vehicles, trains or airplanes can be affected by carbon soot stains. Leaky boilers, gas fires, gas ovens, open fires, and cigarette smoke can also cause carbon soot stains.

However, recent studies show that a common cause of carbon soot stains is the use of candles in the house.

Some candles — particularly those made of low-quality paraffin wax and those using oils for scent — produce more soot than others.

Wick length and the amount of oxygen a candle gets can also cause overproduction of carbon soot.

For example:

  • candles inside jars produce more soot because less oxygen reaches the wick;
  • incorrectly designed candles will burn the wax too quickly, leaving more of the wick exposed;
  • oversized wicks cause the flame to burn too high;
  • any draft passing over the flame will cause the candle to smoke.

To find out if a candle produces carbon soot, burn it on top of a turned-on television. After several hours, wipe the screen with a clean, white cloth or tissue. If there is soot on the cloth, switch to another make of candle.

Several candle manufacturers print warning labels about carbon soot on their packages.

Air movement

Carpets act as filters for airborne particles. For example, if a bedroom door is usually kept closed, the air flow passes underneath the door, and the carpet fibres trap the particles leaving a dark area at the door entrance. 

Because hot air rises, if there are any gaps between the skirting board and the flooring, or gaps in the floor boards, the carpet will trap any rising airborne soot deposits in the fibres. Over time, the carpeting begins to darken above or alongside the gaps. This staining can become quite noticeable, especially in light-coloured carpeting.

How to avoid the problem

Prevention is the best way to reduce or avoid soot staining.

  • avoid light-coloured carpet,
  • keep soot sources out of the house — choose your candles wisely,
  • prevent pollutants from entering the house,
  • prevent air from passing through the carpet.

Keeping soot from entering your house is difficult as the building would require a fairly complicated ventilation system. But preventing air from moving through your carpets only requires some thought, good design, and quality construction.

Air movement in a house requires a pressure difference and an opening. Air can not pass through a carpet if the floor underneath is continuous or sealed. It will only move where there are gaps and holes. These are normally found at the floor-wall junction, staircases, round central heating pipes, or where the subfloor panels or floor boards join together. A continuous air barrier (such as plastic sheeting, hardboard, or a sealed subfloor) will prevent air moving through carpet.

A tightly built house with good draught prevention measures will also prevent carbon soot particles leaking into the house from the outside.

Is this soot a health risk?

Concentrations of particles that cause the staining in carpets are likely to be quite low, however it is not yet clear if low concentrations of carbon soot particles inside a house are still a health risk.


There are several ways to reduce the risk of soot staining. Some do cost more, but they will actually save money by improving energy efficiency in the home. Others can make your house healthier by also reducing dust.

In a new home or during renovation…

  • caulk or seal all holes and gaps including the gap between the floor and skirting boards before installing gripper strips and fitting the carpeting;
  • for forced air heating use a high-efficiency filter on the furnace or an electrostatic precipitator to reduce staining at the air ducts and improve air quality;
  • install a layer of hardwood below the carpet underlay;
  • use area rugs instead of wall-to-wall carpets;
  • have your home, stove, boiler and fireplaces performance tested to ensure they meet all recommendations and specifications.

What Super-Clean will do if you have a problem now…

The staining may not be caused by carbon soot. Dirt and dust stains are usually dark grey in colour, and staining from cigarette smoke is usually dark brown in colour. This staining can normally be very efficiently removed by Super-Clean's powerful deep cleaning hot water extraction machines during a regular carpet cleaning session.

Unfortunately, black carbon soot stains can sometimes be a lot more permanent depending on the type of carpet, type of soot, the amount of airflow, and length of airflow duration. For soot staining along the carpet perimeter, we will usually use a separate tool with a stronger cleaning solution, coupled with repeated hot water extraction to attempt to remove the staining. However, as some staining can change the actual colour of the fibre, some stains can never be completely removed. Very stubborn soot stains on light coloured fibres can sometimes be carefully treated with a special bleaching agent to try and re-match the colour to the rest of the carpet, but the outcome is never guaranteed.

If you feel that your carpet might have soot/draught staining, and you are in the Tyne and Wear area, call Super-Clean Carpet Cleaners in South Shields on 

07708 565 077 

and we can give you a free, no obligation, quotation to have it removed.

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 Steve Hutchinson t/a Super-Clean, 32 Westmorland Road, South Shields, South Tyneside, Tyne and Wear NE34 7JJ Telephone: 07708 565 077 

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