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Soil wicking is the upward flow of material to the surface of face yarns during a drying process. It may occur, as an overall condition, as splotches or as a few spots.
Unique to either condition is that the soil is located only on the tips of the face yarns. These "spots" respond well to cleaning, but return again upon drying.
Both of these issues are virtually identical to cellulosic browning. The difference is that cellulosic browning can't be fixed with alkaline re-cleaning; wicking can be. One should always check both the face yarns and backing yarns to make sure there is not a plant fiber in the carpet.
Looking at a spot on the surface of the carpet doesn't always indicate potential problems. See the next photo.
Soil wicking is one of the more common complaints from end-users and is a common reason why professional cleaners have to return to the job to re-service their customer. Frequently, "reservicing" is not successful, because most professionals have never been taught the ultimate fix or have de-emphasized it due to other advancements in our industry.
In other words, the spot is removed with recleaning, but reappears again upon drying.
Fix the spot
The ultimate fix is to cover potentials wicking problems with a weighted damp terry towel or an adsorbent powder, immediately following the cleaning.
The preferred choice for deeper absorption is a powder and most chemical manufacturers make such a product.
However, a recent informal survey with many supply houses found that very little of this kind of product is being sold. This means cleaning technicians do not understand how to use this kind of product. Civil action by end-users has caused some carpet manufacturers to replace entire rooms of carpet due the ignorance of cleaning professionals.
Surfactants and encapsulants
Increase vacuum-power in hot water extraction machines and encapsulation detergents have reduced the number of wicking spots, but have left many cleaners with a false sense of security on fixing all problems.
There is an inherent contrast in behavior between surfactants and encapsulants. Surfactants are a major component in the mechanisms that cause wicking; encapsulants behave in such a way that it is harder for soil to wick.
The reason surfactants are a component in wicking is because the chemistry is based upon opposite ends. One end loves water and rides on liquid water as it migrates up face yarns during the drying process, while the other end attracts insoluble substances as it migrates up face yarns during the drying process. You can compare this scenario as if you were riding in the bed of a pickup truck. Where the truck goes, you go. For carpet cleaning, where the water goes is where the soil goes. The water that wicks to the surface isn''t always clean water.
Encapsulants, on the other hand, behave more like protectors, making it difficult for soils to find a resting place.
What is in the backing of the carpet and in the pad is what causes most wicking problems.
Anticipate this and avoid costly callbacks.
Another reason some spots wick is because most cleaners do not detect which spots might return.
A simple test might help. Some spots that can wick have detectable moisture that travels deep into an installation. Most types of moisture sensors might detect that moisture before you start the cleaning process. Even a simple sensor with intrusive pins may indicate which spots should be covered in absorbent powders after the face yarns have been cleaned, groomed and dried.
How to use absorbent powders
It's a simple process.
Apply the powder generously; work into the pile of the carpet with a brush or rake, and then cover with a material to prevent tracking or movement of the material.
Whatever you cover the spot with needs to allow drying to occur, so avoid plastics or other non-permeable materials.
The powder will absorb the moisture and soils that would have normally wicked to the surface.
Instruct the consumer how to vacuum up the material once it has dried.
Many of the absorbent powders in our industry are based upon diatomaceous earth. Other industries, such as swimming pool chemical suppliers, use the same kind of material.
Carpet cleaning supply house absorbent compounds are frequently "food grade" products. Most other industries use "technical grade" compounds with antimicrobials.
Ingestion of a product made for carpet cleaning will frequently have no ill affect. Ingestion of something else could be a cleaner''s worst nightmare.
James (Jim) B. Smith is an IICRC-approved instructor and a senior practicing inspector. His educational studies come from Texas A&M University and the University of Houston. He has been in the cleaning industry since 1975. For more information, visit his website at www.CarpetInspector.com/jbs or call (972) 334-0533 or (800) 675-4003.