Have you ever had a spot that just wont go away? Does the spot clean up but within a day it reappears? Most often the reason is do to wicking. As professional carpet cleaners in East TX we run into this often.
Often when a large amount of anything spilled on the carpet the liquid penetrates through the face of the carpet and into the backing. Carpet dries from the tips, so the water you used to clean with is actually moving from the back of the carpet up to the top.
When the water migrates from the bottom of the carpet to the top, it also brings with it the original spill that was never cleaned out of the back of the carpet. When the water evaporates, it leaves the solids from the original spill.
This is not only true for bad spills but also heavily stained carpet as well. When the carpet is cleaned only the face or top part of the carpet is cleared out but the lower area like the backing is saturated. This liquid will pull up the soil to the top just as it will a spill.
Of course this can be remedied. The easiest way to avoid the wicking is to dry the carpet very fast. This is done with a fan placed directly on the spot. Another method is to place a clean white towel over the area after cleaning and weigh it down. This will cause the solids to be absorbed into the towel and not left on the top of the carpet. Also, try not to over wet the carpet when cleaning spots.
It is important to notify your professional carpet cleaner about trouble spots that re-appear so they can take the appropriate steps to ensure your satisfaction.