Kettle
The appliance where limescale appears fastest, because heating hard water is precisely what deposits it.
Precautions
- Disconnect from the power supply first
- Rinse thoroughly afterwards
- Check the manufacturer's instructions
Start here
What this is, what tends to go wrong with it, and what to do about it.
Made from
Which part are you cleaning?
These parts take different answers. Cleaning one the way you clean another is a common way to damage this.
- Kettle filter
A mesh in the spout that catches scale flakes on the way out. It is removable, and it is why some kettles pour clear while scaling badly inside.
Household plastics
Things not to use here
What tends to go wrong
A hard, chalky calcium carbonate deposit left by hard water. Dissolved by acids, essentially untouched by detergents.
Why it is difficult: Water hardness, Crystallisation, Adhesion and cohesion
- Fingerprintsvia its material
Skin oils transferred by touch. A greasy soil rather than a dirty one, which is why water alone does not shift them and why they return immediately.
Why it is difficult: Surfactancy
- Water marksvia its material
What hard water leaves behind when it evaporates instead of being wiped away. A mineral film, not dirt, and the fix is at the drying stage.
Why it is difficult: Water hardness, Evaporative deposition
- Rustvia its material
Hydrated iron oxide from corroding iron or steel. Distinguish a surface deposit, which cleans off, from active corrosion of the item itself, which does not.
Why it is difficult: Corrosion and passivation, Why old stains are harder, Adhesion and cohesion
- Burnt-on food and carbon depositsvia its material
Food heated until it carbonised and bonded to the surface. Time and softening do the work; scouring powder does the damage.
Why it is difficult: Contact time, Carbonisation, Adhesion and cohesion, Why old stains are harder
- Greasevia its material
Fats and oils, which water alone cannot lift. Removed by surfactants, by heat, by solvents, or by alkalis that convert the fat into soap.
Why it is difficult: Why oil resists water, Emulsification
- Heat tintvia its material
The rainbow or brown bloom on stainless steel that has been heated. Not a deposit and not dirt: the metal's own surface oxide, thickened by heat.
The science behind this: Corrosion and passivation, Water hardness, Chloride attack, Cleanability is designed in
In detail
A kettle accumulates limescale faster than almost anything else in a house, for a reason specific to the chemistry rather than to the appliance. The calcium bicarbonate dissolved in hard water becomes less soluble as the temperature rises, so heating drives it out of solution as calcium carbonate, which deposits on the hottest surfaces — the element and the base. Scale is not a hygiene problem and does not make the water unsafe, but it insulates the heating element, which slowly increases energy use, and flakes of it in the water are unpleasant. Descaling is an acid job, and the practical considerations are about the appliance rather than the chemistry: an electric kettle contains electrical components that must not be immersed, and thorough rinsing afterwards matters because whatever descaler is used will otherwise be in the next cup of tea. Kettle manufacturers generally specify a descaling method, and where they do it governs, since it accounts for the materials used in that particular model.
Related
- Kettle has the component Kettle filter
- Kettle is made from Stainless steel
- Kettle is commonly affected by Limescale
Hacks and claims involving this
- Denture cleaning tablets for descaling Unresolved
Sources for this page
Sources
Handbook of Detergents (Surfactant Science Series)
CRC Press / Taylor & Francis · Reference work
Relied on for: That hardness salts precipitate from solution on heating, forming scale deposits.