Carpet cleaning methods, and which one suits your carpet

Hot water extraction

Often called steam cleaning, although it does not use steam. Hot detergent solution is injected into the pile under pressure and drawn straight back out with the soil in it.

It cleans deepest and it is what most manufacturers specify for warranty purposes. The cost is drying time: four to twelve hours depending on the pile, the airflow and the operator, and longer in a cold room with the windows shut. Ask for the room to be ventilated and for fans if the carpet has to be back in use the same day.

Low moisture and encapsulation

A detergent is worked into the pile with a rotary or oscillating machine and crystallises around the soil as it dries. The residue and the soil in it are then vacuumed out, usually the following day.

Drying is one to two hours, which is why offices and hotels use it: the carpet is back in service the same shift. It does not reach as deep as extraction, so it suits maintenance on a regular cycle rather than a carpet that has not been cleaned in five years.

Dry compound

A moist absorbent compound is brushed through the pile, takes up the soil, and is vacuumed away. There is effectively no drying time.

It is the gentlest of the three and the right answer for fibres that must not get wet, including some wool and most natural fibre floor coverings such as sisal, seagrass and jute, which can shrink, discolour or rot with water.

Choosing between them

The fibre decides first. Wool can be wet cleaned but shrinks if it is over-wetted and is sensitive to alkaline detergents. Polypropylene is nearly indestructible and takes extraction well. Natural fibre coverings should usually not be wet cleaned at all. A cleaner who does not ask what the carpet is made of before quoting has not started work yet.

Then the soiling. Heavy soiling and pet odours need extraction, because the soil has to physically leave the carpet rather than be encapsulated in it.

Then the time you have. If the room is needed in two hours, extraction is the wrong choice regardless of everything above.

What to ask, and what a good job includes

A proper job starts with dry vacuuming, because a large share of the soil in a carpet is dry particulate and taking it out first stops it becoming mud. Then a pre-spray with dwell time, then agitation, then the clean itself, then grooming the pile.

A visit that begins with the wand and ends twenty minutes later has skipped the two stages that do most of the work. The National Carpet Cleaners Association maintains a public member list, and membership is one of the few things in this trade that can be checked rather than claimed.