Limescale

Limescale is the deposition of salts of calcium and other metals contained in hard water (see Wikipedia article). The build-up of limescale can impair the efficiency of heat exchanges (e.g. in Combination Boilers) and block water pipes. Thin films of limescale can form on the smooth surfaces of baths, basins, WC pans, and glasses and crockery etc, allowing dirt to adhere.

Limescale is not readily soluble in water but may be removed with various acids

Causes of Limescale

Limescale derives from the salts dissolved in hard water. Two mechanisms result in limescale deposits:

1. Deposition of salts causing temporary hardness when water is heated. This is the main cause of scaling of boilers, heat exchangers, hot water cylinders and kettles.
2. Deposition of the salts causing both temporary and permanent hardness as water evaporates. This is the cause of scale deposits on tap spouts, WC pans and other sanitaryware and glasses and crockery allowed to dry naturally.

Effects on Appliances

Limescale tends to collect most on heating elements and heat exchangers. There are 2 different effects this can have.

Fixed power devices, such as all electric heating elements, will transfer the same amount of heat, but the element temperature will run hotter.

Fixed or limited temperature sources, such as anywhere hot water is the heat source, and solarthermal panels, will transfer much less heat when scaled. This is true of more or less all heat exchangers.

Prevention

Ion Exchange Water Softener

• Removes calcium ions, replacing them with sodium ions.
• A complete cure for scaling
• Requires top-ups of salt
• Equipment expensive
• May cause corrosion in plumbing fittings

Phosphate Dosing Scale Inhibitor

• 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 http://en.wikipedia.org/wiki/Sodium_tripolyphosphate

Manufacturers

• 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")

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.

Regular use of lime scale removing acidic cleaner

• Helps prevents buildup

Removal

• 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.

Chemicals

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

Vinegar

• 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.

Safety

• 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.

Goods

Baths, plastic

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

Baths, enamel & cast iron

Some acids may damage enamel (need to check this)

Shower curtains

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

Tiles

• 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.

Kettle

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

Washing machine

Add citric acid, don't 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. (There is no need for multiple rinses and spin.)

Limescale prevention tablets (eg Calgon) can slightly reduce the risk of some washing machine failures - and increase some - but the cost of tablet use far exceeds the cost of repair, and periodic use of citric acid is as effective and far cheaper. So there is no real basis for recommending such products.

Chromework, Taps

• plastic scourer
• heat the chrome with boiling water and apply vinegar. Rub with plastic scourer or coarse cloth.
• Proprietary limescale remover containing sulphamic acid and anionic surfactant: apply with J-cloth; in case of heavy encrustation wrap cloth around metalwork and soak in remover, leave for 15-30 minutes and wipe or rub again.

Stainless Steel

• Tomato ketchup
• plastic scourer
• copper scourer
• Proprietary limescale remover containing sulphamic acid and anionic surfactant

UPVC

• any acids

Othernyms

Hydrochloric acid

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

Sulphamic acid

Fernox DS3

Sulphuric acid

Battery acid, vitriol

Suppliers

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

See Also

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