What causes that dark line on my carpet around the baseboard?

        An old friend of mine from the Insurance renovation business sent me a question this morning regarding a flooring issue that he had seen but didn't know what caused it.. Its called "Filtration", very common & still a mystery to a lot of folks. SO! I thought since I had already answered it for him I would share it with the rest of you so we are all a little better informed & able to win that $2,000 double Jeopardy question when you someday find yourself saying.. "Weird flooring trivia for a $2,000 Alex!"

         The HVAC system (furnace) creates a slight positive pressure (In fact a negative pressure would do it too, so I suspect DRYERS are contributing factors!) inside the house by bringing in a little fresh air each time it is running.

         The houses today are so tightly sealed & insulated to keep energy loss to a minimum that the added fresh air creates positive pressure inside the home which tries to find a way to equalize.

         One of the gaps in most homes that is seldom sealed well enough is where the stud wall meets the decking/subfloor, so the airs squeezes through the gap where the wall meets the floor (at the baseboard!)...

          That endless stream of escaping air, year after year carries all things small & airborne like fireplace soot, Gnomes, cooking grease, Dryer lint, MOLD, soot from candles & air fresheners and dust as the air seeks to equalize pressure. The carpet yarn acts as a really efficient filter & the "soot" sticks to it & builds up over the years, till you see it.

        The fact that the color pallet for flooring has lightened a lot in the last 30 years and homes have been better insulated means we see it more than we did on our Brown shag in the 70's.  It is usually a perfect gray or darker outline about an inch wide, around the perimeter of the room right at the baseboard.

      Interestingly & logically it doesn't always happen on interior walls (less pressure gradient differential among inside rooms) unless the vents in the adjacent rooms are closed, causing a difference in airflow/pressure.  Mostly its the exterior walls of a home & stairs are notoriously commonly effected where the pressure easily leaks to the lower outside ambient pressure.

     I have seen it in the middle of a floor where you could literally trace the 4'x8' sheets of plywood or the decking boards back in the days when 1"x12" was used for decking. and it sometime happens right under a door that stay closed all the time. 

The Brits call it "Draught (Draft! Darned Brits spell funny!) marking", in the US most folk

s call it "Filtration"

Hope that helps & thank you google images for letting me borrow those pics when I couldn't find mine!!

Just for the RECORD it is not a carpet defect, not the mills fault nor is it the Retailer or the Installers fault. If anyone is at fault it would be the HVAC system installer or the Builder for not sealing that GAP! It is really tough to remove because it is years of built of gunk but that would be between you and your Carpet Cleaning specialist!

In summary now you know about Carpet Filtration AND you know why my vast knowledge of useless stuff doesn't get me invited to dinner parties & cocktail parties.

Thanks & hope this helps

Thus saith the Rev!

Don Barrett

President & CEO

FAST Career Institute

Office: 864.498.4260
Cell: 765.238.0102