A stronger solution cleans better

Does it work?

Does not work

Refuted for carpet by an explicit trade instruction. The surfactant-saturation mechanism generalises, but CleaningHQ states the refutation only where a source states it.

This is a verdict on whether the technique is effective. Whether it is safe on a particular surface is a separate question, answered below.

Where not to use it

Why it works

More surfactant means more cleaning is a reasonable extrapolation and is wrong past a point, because surfactant action saturates: above the concentration at which micelles form, additional surfactant contributes little further soil removal and a great deal more residue. The residue is the problem, since it cannot be evaporated away and holds soil against the fibre.

Background

Doubling the dose is the most natural response to a mark that will not shift, and it is the one instruction the carpet trade association chose to shout. Its spot procedure specifies a quarter teaspoon of liquid dish washing detergent per cup of lukewarm water and adds, emphatically, never to use a stronger concentration. The precision is the evidence: a body that publishes a dilution to the quarter teaspoon and forbids exceeding it is making a statement about what harms carpet rather than about economy. The same guidance rules out two whole product categories — laundry detergent and automatic dishwasher detergent must not be used, because they can damage fibres or cause discolouration — which is a useful corrective to the assumption that detergent is detergent. The mechanism behind the rule is residue. Surfactant left in a fibre does not evaporate; it stays, stays sticky, and attracts soil, so an over-concentrated treatment produces a patch that resoils faster than the carpet around it and looks dirty again within weeks. That is why the procedure ends with rinsing and blotting until no moisture remains rather than at the point the stain disappears.

What it does not do

• The specific dilution is the carpet trade's and applies to carpet rather than to every surface
• The prohibition on laundry and dishwasher detergent is stated without a stated mechanism

What to use instead

• Blotting — Lifting a spill straight up into an absorbent cloth rather than working at it. The opposite of what almost everyone does, and the trade bodies are explicit about why.
• Soaking — Extending contact time so chemistry can do work that would otherwise need force. Often the difference between scrubbing and wiping.
• Water — The solvent almost all cleaning happens in, and on its own the right answer more often than it is given credit for.