Sodium carbonate
A considerably stronger alkali than bicarbonate. Effective on grease and as a laundry builder, and damaging to aluminium, wool and painted surfaces.
What not to do
These are the combinations an authority has warned about. It is not a list of everything dangerous: a substance nobody has warned about has not been cleared, and none of this is permission to mix.
Never mix
Chlorine gas is released. The regulator lists soda ash — washing soda — among the substances sodium dichloroisocyanurate is not compatible with, alongside ammonia, amines, strong bases, oxidising agents and hydrogen peroxide. Chlorine irritates the eyes, nose, throat and lungs and its effects can be delayed. Ventilate by leaving, not by staying.
Sodium carbonate is unsafe on Aluminium
Unsafe
Do not do this. The risk is established, and it is described below.
Aluminium is amphoteric: strong alkali dissolves the protective oxide and then attacks the metal, leaving a dull grey or blackened surface that is not a deposit.
Precautions
- Wear gloves
- Test on an inconspicuous area first
Evidence
Strongly supported
Sources
Safety Data Sheet: Sodium Carbonate
Murphy and Son Ltd · Manufacturer documentation
Relied on for: That the supplier's safety data sheet lists ALUMINIUM among the materials to avoid for sodium carbonate, under section 10.5, Incompatible materials. (states this directly)
Kirk-Othmer Encyclopedia of Chemical Technology
John Wiley & Sons · Reference work
Relied on for: That aluminium is amphoteric and that its protective oxide film is dissolved by strong alkali. (background and mechanism only)
Sodium carbonate is unsafe on Wool
Unsafe
Do not do this. The risk is established, and it is described below.
Precautions
- Check the manufacturer's instructions
Evidence
Supported
Sources
Best detergent to use when washing wool
The Woolmark Company · Trade or professional body
Relied on for: That heavy-duty detergents are advised against for wool in favour of a mild or neutral detergent with a relatively neutral pH. (applied to this case rather than stated directly)
Kirk-Othmer Encyclopedia of Chemical Technology
John Wiley & Sons · Reference work
Relied on for: That alkaline hydrolysis degrades protein. (background and mechanism only)
Sodium carbonate may damage Painted and coated steel
Best avoided
The available guidance advises against this.
A state hazardous substance fact sheet records that sodium hydroxide attacks coatings.
Precautions
- Wear gloves
- Wear eye protection
- Test on an inconspicuous area first
Evidence
Supported
Sources
Right to Know Hazardous Substance Fact Sheet: Sodium Hydroxide
New Jersey Department of Health, Right to Know Program · Government or regulator
Relied on for: That sodium hydroxide can attack iron, copper, plastics, rubber and coatings. (states this directly)
Sodium carbonate may damage Coated aluminium
Best avoided
The available guidance advises against this.
The alkaline half of the same prohibition. Soda crystals are the domestic form most likely to reach a garden table.
Evidence
Supported
Sources
AAMA 609 & 610-02: Cleaning and Maintenance Guide for Architecturally Finished Aluminum
American Architectural Manufacturers Association (AAMA), 2002 · Standards body
Relied on for: That aggressive alkaline cleaners must never be used on aluminium finishes, and that alkaline materials allowed to dry on the metal will quickly corrode anodic coatings. (states this directly)
Sodium carbonate is unsafe on Finished leather
Unsafe
Do not do this. The risk is established, and it is described below.
Standing in for the high-pH class the guide prohibits. Soda crystals are the alkaline product a domestic reader is most likely to reach for.
Evidence
Supported
Sources
Leather Care and Cleaning Guide
The Leather Institute, 2011 · Trade or professional body
Relied on for: That any high pH cleaner must never be used on finished leather, and that caustic household cleaners are named among the products that may cause cracking or other damage to water-based finishes. (states this directly)
Sodium dichloroisocyanurate must never be mixed with Sodium carbonate
Unsafe
Do not do this. The risk is established, and it is described below.
Soda ash is washing soda. The regulator lists it among the substances the chlorine donor is not compatible with, and nothing on either package suggests a connection.
Precautions
- Never mix with other cleaning products
- Ventilate the area
- Keep away from children and pets
Evidence
Strongly supported
Sources
Right to Know Hazardous Substance Fact Sheet: Sodium Dichloro-Isocyanate (RTK 1694)
New Jersey Department of Health, 2002 · Government or regulator
Relied on for: That sodium dichloroisocyanurate is not compatible with soda ash, ammonia, amines, strong bases, oxidising agents and hydrogen peroxide. (states this directly)
Precautions
- Wear gloves
- Never mix with other cleaning products
- Rinse thoroughly afterwards
In detail
Sodium carbonate is a substantially stronger base than sodium bicarbonate, and the difference between the two is often lost because their household names sound alike. It attacks grease by saponification, converting fats into soaps that then dissolve, which makes it effective on heavy greasy soil where a mild cleaner is not. In laundry it acts as a builder, softening water by precipitating calcium and magnesium so that surfactants are not wasted on hardness. Its strength is also its restriction. As a strong alkali it attacks aluminium, which is amphoteric; it hydrolyses protein fibres, so it is inappropriate for wool and silk; and it can damage paint, varnish and some sealants. It is the right tool for a specific set of jobs and a poor general-purpose cleaner.
Properties
- Chemical name
- Sodium carbonate
- pH
- Alkaline
What works
Sodium carbonate is effective against Grease Supported
Sodium carbonate is effective against Tea Supported
A hot washing-soda soak, named for tannin staining specifically.
Sodium carbonate is effective against Protein soil Supported
Alkali is the tool for protein. Not heat, and not a stronger surfactant.
Why
- Sodium carbonate is explained by pH in cleaning
A considerably stronger alkali than bicarbonate, and the strength is both what it is for and what restricts it.
Hacks and claims involving this
When the obvious answer is wrong
Can I use a limescale remover on the grout in my shower?
Cementitious grout is alkaline based and is dissolved by acids — the tile trade states this plainly and draws the conclusion itself, that manufacturers do not advocate acids because they attack the cement in the grout. Grout is also porous, so an acidic product does not merely touch the surface. The damage is gradual and looks like wear rather than like chemical attack, which is why it is rarely attributed to the cleaner that caused it.
A different kind of treatment works: Use an alkaline cleaner rather than an acidic one. This is the tile trade's stated preference for grout, and it has the convenient property of matching what the other common soil in a shower actually needs — soap scum and body oils are greasy soils that respond to alkali and surfactancy, not to acid. Where the grout is epoxy rather than cementitious the constraint does not apply in the same way, since epoxy grout is described as virtually as stain-proof as the tile, but check which you have before assuming. As with stone, drying the surface after use does more than any product: the deposit forms when hard water evaporates in place.
Can I use oven cleaner or a strong degreaser on aluminium?
Aluminium is amphoteric — attacked by strong bases as well as by strong acids. The alkali dissolves the protective oxide film and then the metal beneath, leaving a dull grey or blackened surface that is not a deposit and cannot be cleaned off. There is a second consequence that is a safety matter rather than a cosmetic one: a US state hazardous substance fact sheet records that sodium hydroxide reacts with metals including aluminium to form flammable and explosive hydrogen gas, which is not what anybody expects from cleaning an oven tray in a confined space.
A different kind of treatment works: Take the contact-time route instead of the chemical-strength route. Soaking in hot water with an ordinary detergent softens polymerised soil given long enough, and repeating a mild treatment is the trade's stated sequence for burnt-on deposits precisely because the aggressive alternatives damage surfaces. Where the item is unquestionably steel rather than aluminium the caustic route is available, so the first thing worth establishing is which metal you have — aluminium trays and steel trays look similar and behave completely differently. If a caustic product has already been used, ventilate and do not enclose the item while it is reacting.
What should I use on a greasy mark on a wool jumper?
Wool is a protein fibre, and the mechanism that converts fat to soap also hydrolyses protein. A strong alkali therefore attacks the garment on the same chemistry it uses on the stain, and the damage is to the fibre rather than to its appearance — it is not a mark that can be cleaned off afterwards. The wool body approaches the same problem from the other end, warning that methods primarily aimed at garments made from cotton or synthetic fibres are not all suitable for wool, and specifying a dilute wool detergent in TEPID water rather than anything stronger or hotter.
A different kind of treatment works: Change the mechanism from saponification to dissolution, and respect the order. The wool body's instruction for oily or greasy stains is that they are best treated with SOLVENTS FIRST, and that the solvent MUST BE ALLOWED TO EVAPORATE before any water-based treatment is subsequently carried out. That waiting step is the part most likely to be skipped and it is stated explicitly. The water-based stage that follows is a dilute solution of an approved wool detergent in tepid water — dilute rather than strong, tepid rather than hot. Technique carries the rest: scoop or blot the excess quickly with white tissue or an absorbent towel, work from the edge of the mark towards the centre, and do not rub. Where the mark survives that, the honest next step is professional cleaning rather than a stronger alkali.
Sources for this page
Sources
Handbook of Detergents (Surfactant Science Series)
CRC Press / Taylor & Francis · Reference work
Relied on for: That alkaline builders such as sodium carbonate address water hardness and contribute to the removal of fatty soils.