The pH Guide: Which Chemistry Removes What
Every mark on a car falls into one of five types, and each type has one chemistry that removes it. Match the chemistry to the dirt and you clean faster, scrub less and protect your paint.
- Organic: bugs, traffic film, grease, tyre browning → alkaline. Bug removers · Snow foam · Wheels & tyres
- Mineral: water spots, limescale → acid. Water spot removers
- Iron: embedded brake and rail dust → iron remover. Use it as maintenance, every few months. Iron removers
- Oily: tar, sap, adhesive → solvent. Like dissolves like. Tar & adhesive
- Physical: overspray, bonded grit → clay, only when polishing afterwards. Clay
The order: alkaline first, then acid, then a neutral wash. Use iron and solvent steps only when needed.
The everyday wash: a pH-neutral shampoo on protected paint. Shampoo
Inside the car: leather gets pH-neutral cleaners only. Fabric takes alkaline for organic stains and mild acid for tide marks. Leather · Fabric
Common questions
What pH should a car shampoo be?
For the everyday contact wash on protected paint, neutral (around pH 7). It cleans by surfactants and lubrication and leaves wax, sealant and coatings alone.
What removes water spots?
Acid. Water spots are calcium and magnesium minerals, and they dissolve in acid, not in alkaline or neutral cleaners. A spot that stays after an acid step is etched into the clear coat and needs polishing.
Do I need a dedicated insect remover?
Not always. Bug residue is mostly protein and fat, which alkaline cleaners break down, so a good alkaline pre-wash removes fresh bugs. Dedicated removers are thicker, so they cling and stay wet for spot work.
Can I use an iron remover every wash?
Used as directed it's safe, but we use it as maintenance every few months. A brake disc is iron, so an iron remover strips it bare and it flash-rusts, throwing orange dust back onto clean wheels. For weekly washes we use an alkaline wheel cleaner.
Why do tyres go brown?
The tyre's ozone protectant (6PPD) migrates to the surface and oxidises brown. It's oily and won't wash off with water or an iron remover; an alkaline tyre cleaner removes it.
When should I clay my car?
Only when the paint will be polished afterwards. Clay can leave light marring even with plenty of lubricant, and alkaline, acid and iron steps remove most contamination without touching the paint.