What is Limescale?
Scale forms when hard water is heated above 140°F (61°C) or when it is allowed to evaporate on surfaces such as faucets and shower heads. Hard water is water that contains high amounts of calcium and magnesium ions. These hardness minerals, in the form of calcium carbonate and magnesium carbonate, are what precipitate out of hard water to form lime. Therefore, to clean or remove limescale, we need something that dissolves or softens calcium carbonate and/or magnesium carbonate.
Acids are generally very good at dissolving things, and in particular the following list of acids will dissolve limescale.
Warning: Some of these acids are extremely dangerous and their use as a descaler is best left to professionals. Also, some acids, particularly hydrochloric acid, will discolor (blacken) chrome faucets and fixtures.
1) acetic acid
Vinegar is just diluted acetic acid, so it’s readily available in the home.
Mix half a cup of water and half a cup of white vinegar (not malt vinegar) to descale an electric kettle. Bring the mixture to a boil and leave overnight. Rinse the next day.
Clean shower heads by soaking them overnight in a tub of undiluted white vinegar. Mix with borax (50:50) to make your own inexpensive anti-scale cleaner for faucets, tiles, bathtubs and sinks.
2) citric acid
Citric acid is present to some degree in all citrus fruits, but lemons generally have the highest concentration. Lemon juice generally works better than vinegar and leaves a more pleasant scent.
To clean dishwashers and washing machines, use a cup of lemon juice instead of regular detergent. Run a normal wash cycle without clothes or dishes. For washing machines, put the lemon juice in the soap powder dispenser. Dishwasher safe, only to fit directly into the bottom of the machine.
To clean electric kettles, follow the directions for vinegar, but replace the vinegar with lemon juice. Same for shower heads.
When it comes to cleaning the taps, the problem comes when trying to keep the lemon juice in contact with the lime long enough for it to dissolve or soften. One way to overcome this problem is to soak a cloth in lemon juice, wrap it around the faucet, and leave it overnight.
Citric acid is also the main component of Limelite sprays, gels, descaler and wipes.
3) formic acid
Formic acid, naturally produced by ants and contained in bee stings, will dissolve limescale. It can be purchased as Kilrock K or in diluted form as Techno Swan. It is also one of two acids used in Cillit Bang Grime and Lime (the other being sulfamic acid).
4) glycolic acid
Although primarily used in cosmetics, glycolic acid is a secondary ingredient in several commercial limescale removers, including R8 Kettle Descaler. DuPont markets glycolic acid to remove hard water scale deposits in boiler and industrial water systems.
5) hydrochloric acid
Sold in Spain as agua fuerte (strong water). Be careful, hydrochloric acid is a strong acid and will burn the skin; Please read all safety data carefully. It bubbles on contact with lime and the vapor it gives off (hydrogen chloride) is toxic, so it’s probably best left to the experts.
If you still want to give it a try, then a safer alternative, which contains hydrochloric acid as its main active ingredient, is No Nonsense Path Patio & Driveway Cleaner. Other kitchen and bathroom cleaners that contain hydrochloric acid include Harpic Duraguard Descaler and Lifeguard Descaler.
6) lactic acid
Sometimes known as milk acid, lactic acid is also a good limescale remover. Lactic acid is formed when lactose, which is found in milk, is broken down by bacteria and is therefore found in sour milk. However, we do not recommend trying to remove limescale with sour milk. Instead, buy some Oust. Oust All Purpose Descaler contains 30 to 50 percent lactic acid and can be used to clean kettles, coffee pots and irons.
7) oxalic acid
Oxalic acid is 3,000 times stronger than acetic acid and is used primarily as a bleaching agent or rust remover. It will remove limescale but is rarely used in household cleaning products. It is used in Oxal Wash to remove limescale (among other things) from the exteriors of trains.
8) phosphoric acid
The primary use of phosphoric acid is as a rust remover, but it is also used in many commercial limescale cleaners and is found in some soft drinks, especially colas.
In the movie Limescale, the main character stops drinking water and only drinks cola because he thinks limescale is building up in his body and the cola will dissolve the hardened deposits. Urban Myth according to the synopsis of the film, but the two main brands of cola contain phosphoric acid (E338).
Phosphoric acid is sold raw as a descaler on eBay and is used in many commercial limescale cleaners. Proprietary cleaners containing phosphoric acid include HG Professional Limescale Remover or Hagesan Blue.
9) sulfamic acid
Sulfamic acid is widely used in commercial limescale cleaners and is a less hazardous alternative to hydrochloric acid. For professional use it is an active ingredient in Fernox DS3 scale remover and at home it is one of the components of Cillit Bang Grime and Lime.
10) sulfuric acid
Knock Out Drain Cleaner is almost pure sulfuric acid, but it is not marketed as a limescale cleaner (although it will do the job). Sulfuric acid is extremely dangerous and is best left to the experts. Even then, few if any descaling products on the market contain sulfuric acid. Avoid!