There are four main methods for professionally cleaning carpet. The following is a brief description of each one:
Hot Water Extraction (Steam Cleaning)
This method most commonly uses truck mount units, but they also use portable units to reach where the hoses can't. This method is very complicated and requires a trained professional with experience to obtain satisfactory results. Due to complexity, equipment used, cleaning chemicals and operator expertise there is a tremendous variance in the quality of the cleaning method. Improper technique can lead to overwetting, possibility of mold growth, stretching, stains reappearing known as wicking, buckling and rapid resoiling due to chemical residue.
Wet Extraction with Carbonation
This is a patented cleaning method used by a dry franchise. It is based on the same premise that club soda will "lift" a spill from fabric. The company uses portable machines that deliver a hot carbonated solution to the carpet.
Both of these methods listed above use water to suspend the dirt and therefore are only as effective as the suction power that removes the moisture from the carpet. The cleaning agents used may well be effective, however, if the soil is not removed from the carpet with the moisture then it will resettle as the carpet dries.
Bonnet Buffing
This method uses much less water to clean than hot water extraction. A floor machine is used to rotate an absorbent cleaning pad over the carpet to absorb the soil and cleaning solution that has been applied to the carpet. This method of soil extraction is not very effective.
Foam Encapsulation Technology (Uses Low Moisture)
Encapsulating Cleaning Foam has crystalline polymers in addition to detergents and Bio-enzymes. After the detergents have attracted and surrounded the dirt and grease the polymers encapsulate both the detergent and soil. As this encapulated soil dries, it crystallizes into a dry (not sticky) residue. This is achieved by the dual brushing action of the machines. Once this process is completed and the stains are removed, the carpet is almost dry and is then vacuumed, leaving the carpet completely clean restored and dry. The stains removed are permanent since the fibres are not left wet.
This is clearly the far superior choice for carpet & upholstery cleaning.
