Trisodium Phosphate — Frequently Asked Questions

Because its solution is strongly alkaline, around pH 12, and strong alkali saponifies fats and oils, converting them chemically into soluble soaps that rinse away. A neutral detergent can only emulsify grease; TSP actually reacts with it. That is also why it etches and degreases painted surfaces enough to provide a key for repainting.

No. It attacks aluminium and can damage some paints, varnishes and soft metals, and it is corrosive to skin and eyes. It should not be used on aluminium vessels or trim, and surfaces should be tested in an inconspicuous area first. Where alkaline cleaning of aluminium is required, sodium metasilicate is the appropriate choice because the silicate passivates the metal.

Phosphate discharge restrictions. Phosphate is a nutrient that promotes algal growth in receiving waters, and eutrophication rules in many jurisdictions limit or prohibit phosphate in domestic cleaning products. Phosphate-free substitutes based on carbonates, silicates and citrates have largely replaced it in consumer cleaners, though industrial use continues where discharge is controlled.

Water of crystallisation. The anhydrous salt contains no bound water and is more concentrated per unit weight; the dodecahydrate carries twelve water molecules per formula unit and is correspondingly weaker. Both are supplied, and the hydration state should be specified because it changes the active content substantially.