Walk off mats - Sink or Source?
Are they doing what you thought they were?
Stop & take a look at them. Are they clean and shiny? Or are they dull, dirty & gray?
If they are shiny and clean then they are removing the soil from your shoes and trapping it in the fibers before you enter the house.
If, on the other hand, the mats are dull, gray and dirty they have become the “Source” of dirt and oil and etc. that you pick up before entering the house. Dirty mats are easily overlooked and add to the resoiling of your carpets.
The rule of thumb is: It takes 15 feet of fuzzy material (carpet) to remove 50% of the soils from the bottom of your shoes. If you replace the first 10-20 feet from the door with tile, or some other hard surface the above rule still applies. No soil is removed from the shoe on a hard surface. All you have accomplished is eliminating the carpet soiling in the tile area – the rule still applies when the fuzzy is reached.