From DIYWiki
Revision as of 05:20, 4 January 2007 by NT (talk | contribs) (changed cateogries to categories)
Jump to navigation Jump to search

Limescale is a film or build up of calcium salts. Since it is rough it can harbour dirt.

Tea stains contain limescale, and may be removed from ceramics and glass with acid.

Cause of Limescale

As water containing dissolved calcium salts evaporates, the calcium salts crystallise and adhere. Hard water is water containing these salts.


Ion Exchange Water Softener

  • Removes calcium ions, replacing them with sodium ions.
  • Requires topups of salt
  • Equipment expensive

Phosphate Dosing

  • cartridge fitted to water pipe, or bag in cold water storage tank; requires periodic replacement

The types fitted to pipework generally have a reservoir of phosphate salt which is fed a trickle of water from the main flow passing through the inhibitor via narrow waterways, so that a small amount of salt is added to the flow. These types are prone to suffering from a build-up of re-crystallised salts which block the narrow waterways preventing further dosing of the water. Routine maintenance must include clearing any such blockages to restore dosing. This must be done mechanically as there is no common substance which will readily dissolve the recrystallised material. (Source: discussion between author and tech support at Permutit --John Stumbles 10:40, 21 December 2006 (GMT))

See also Wikipedia article on Sodium Tripolyphosphate


  • Permutit
metal cased cylindrical cartridge
  • Combimate
wall-mounted with perspex domed window containing mothball-like salt crystals
  • Fernox - Quantomat
clear plastic container suspended from pipework adapter containing phosphate powder ("Quantophos")

Regular use of lime scale removing acidic cleaner

  • Helps prevents buildup

Magnetic, electromagnetic and electrolytic scale preventers

Which? magazine once claimed to have found that some of these could be effective in some circumstances, but it was not possible to predict whether they would be so in specific installations.

Scientific evidence for their effectiveness remains elusive.

In practice it would seem unwise to rely on these types of device for protection of expensive appliances such as combi boilers etc.

Stainless steel wool ball in kettle

  • The scale deposits on the small scourer-like ball. Since the metal is thin & flexible, the scale breaks off in little pieces and is emptied down the sink with the water.


  • acids
  • scrapers and abrasives:
    • plastic scourers remove minimal deposits.
    • copper scourers remove more deposits, but will damage tile grout and plastics
    • aluminium scrapers remove tougher deposits than copper scourers. Not available in shops, use a small piece of very thin sheet ali a fraction of a mm thick.
    • steel scourers are hard enough to damage nearly all materials found in modern homes. May be used on steel where very light scratching is acceptable. May be used on glass, but only gently or scratching can occur.
  • very heavy encrustations are removed with a needle drill, eg at municipal waterworks.
  • Cotton buds are useful when acid is applied to some parts but must be kept off others.


Hydrochloric acid

  • Strongest of all limescale removers
  • Fizzes on contact with limescale
  • Handle with care
  • Avoid all contact with metals, grouts, mortar, concrete, cement based blocks, lime based paints, natural fibre fabrics
  • Slowly dissolves eyeballs & other human parts
  • Wash off skin promptly
  • Darkens crazed patterning on ceramics
  • Discolours (blackens) Chromed fittings

Inhibited Formic Acid

(Sold as Kilrock K)

  • Very effective - acts rapidly
  • Fumes are irritating, especially if spread over a wide area e.g. descaling a bath or shower cubicle.

Sulphuric acid

  • Sulphuric acid may be used for limescale removal.

Sulphamic acid

  • Does not darken crazing of ceramics
  • Does not dscolour Chromed fittings

This can be found combined with anionic surfactant in some bathroom limescale removers. It is very effective in cleaning lightly-scaled baths, showers and fittings. If used frequently (weekly or so) only a wipe-over with such a cleaner on a cloth is required. For moderately scaled taps etc wrapping a cloth soaked in the liquid around the affected parts and leaving for 5-10 minutes makes it easy to then remove the scale.

Phosphoric acid

  • found in some commercial limescale removing cleaners


  • Cleans chromework such as taps

Citric acid

  • Mildest of all
  • A common food ingredient
  • Very slow acting
  • Requires heat to be effective
  • Suitable for washing machines, aluminium, and unknown or mixed materials.


  • Never allow acids to come into contact with bleach. People have died from doing this. If it occurs, don't wait around to figure out what happened, evacuate the area immediately. It only takes a few breaths of chlorine to kill.
  • Stronger acids eat clothes, cement and lime based products, metal, eyes and other parts of humans. Use HCl with care.
  • All acids react with copper to create toxic runoff. Wash away residues to avoid any contact with food or food preparation equipment.


Baths, plastic

Any of the acids listed will work, but the stronger ones damage chromework if contact occurs.

Baths, enamel & cast iron

Shower curtains

  • Any of the acids listed will work, except those requiring heat (vinegar, citric acid)
  • Limescale on curtains retains water and encourages mould


  • All acids damage tile grout, so apply to tiles with care. A cotton bud can be used to get acid close to grout without getting it on the grout.
  • Plastic scourers & scrapers are effective for mild scale
  • Copper scrapers are more effective on tiles but will break up tile grout.


Add citric acid, boil, let sit until cold, rinse clean.

Washing machine

Add citric acid, dont put any clothes in. Set to a 95 degree C or boil wash. When the water reaches boiling, switch the machine off and leave overnight. Switch on in the morning and let it complete its wash program.

Chromework, Taps

  • plastic scourer
  • heat the chrome with boiling water and apply vinegar. Rub with plastic scourer or coarse cloth.

Stainless Steel

  • Tomato ketchup
  • plastic scourer
  • copper scourer


  • any acids


Hydrochloric acid Brick acid, Patio cleaner, HCl, Spirits of salt, Bowl cleaner

Sulphamic acid Fernox DS3

Sulphuric acid Battery acid, vitriol


Hydrochloric acid Builders merchants, online BMs.

Sulphamic acid builders merchants, plumber's merchants

Citric acid chemists. Supermarkets also stock products containing citric acid at inflated prices.

Limescale removing toilet cleaners may contain any of several acids, but are invariably weak mixtures.

Other descalers

Any acid will work as a descaler. Adding salt to mild acids increases their action. Examples of other descalers include:

  • tomato ketchup
  • orange juice
  • steel balls

NT 2006 + others