Washing soda as a general-purpose cleaner

Does it work?

Disputed

Recorded as disputed rather than supported or refuted, because the two halves genuinely diverge. Marking it supported would endorse the general claim including its damaging applications; marking it refuted would deny an effectiveness nobody sensible denies. Disputed with the dissent stated is the shape of answer this model exists to give.

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

Sodium carbonate dissolves to give a strongly alkaline solution. Alkalinity saponifies fats and oils, converting them into water-soluble soaps that rinse away, and it also softens water by precipitating calcium and magnesium, which is why it was the original laundry booster and where the name comes from. Both mechanisms are established and neither is in dispute. What the popular claim leaves out is that the same alkalinity is what attacks aluminium, zinc, painted finishes, oiled wood and protein fibres, and that the effect is not a side effect but the same property meeting a different material.

Background

Unlike most claims in this register, the effectiveness half of this one is not in doubt. Sodium carbonate is a genuinely strong alkali — far stronger than bicarbonate of soda, with which it is constantly confused — and alkaline degreasing works by converting fat into soap, which is the same reaction that makes oven cleaner effective. Where the claim fails is in the word general. An alkali strong enough to saponify grease is strong enough to attack the light metals, and four separate regulator fact sheets in this register establish the pattern: aluminium, zinc, tin and galvanised iron are corroded by alkalis, producing hydrogen as they go. Aluminium is the one that matters, because soaking pans, bakeware and moka pots in soda crystals is one of the most-promoted uses of the product and it dulls and pits them permanently. Two further limits. On painted, lacquered and oiled wood an alkali strips the finish. And there is a hazard as well: the regulator lists soda ash among the substances a chlorine-releasing tablet must not meet, and both are promoted for soaking.

Conditions

• Dissolved in hot water
• Not on aluminium, zinc or galvanised metal
• Not on protein fibres

What it does not do

• It is a degreaser, so it does nothing useful against limescale, rust, tarnish or any mineral deposit.
• It is confused with bicarbonate of soda constantly, and the two are not interchangeable in either strength or effect.
• It leaves an alkaline residue, so surfaces need rinsing rather than wiping.

What to use instead

• Neutral cleaning — The default that four separate trades converge on independently: a neutral detergent, warm water, a soft tool and a thorough rinse.
• Detergent — A surfactant-based cleaner. The general-purpose answer for greasy and particulate soil, and the correct first choice far more often than any specialist product.
• Sodium bicarbonate — A mild alkali that is also a fine, soft abrasive. Its real usefulness is mechanical, and it is far weaker chemically than its reputation suggests.
• Descaler — A product category rather than a chemical: an acid chosen to dissolve carbonate scale. Which acid decides which surfaces the bottle will ruin.