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
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
Why we say this
Strongly supported
CLOSED IN SPRINT 7, after four sprints of audit notes. The incompatibility is now stated by a document that was read: a safety data sheet naming aluminium under materials to avoid. Note precisely what changed and what did not. The COMPATIBILITY FACT is now directly evidenced, which is why this moves to strongly supported. The MECHANISM is not: the sheet gives no reaction, no product and no consequence, so the amphoteric account in the note above remains an interpretation from general chemistry and keeps a background citation rather than being promoted alongside it. Sprint 6 found the equivalent statement for sodium HYDROXIDE and declined to carry it across to carbonate; this is the carbonate-specific evidence that refusal required, and it was worth waiting for.
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)
Verification: a person has read the passage relied on.
Read on — Section 10.5, Incompatible materials. Supports a narrower statement — our claim was reduced. The incompatibility itself is now directly evidenced by a document that was read, and the sodium-carbonate-on-aluminium edge no longer rests on two unread reference works. What is NOT evidenced by it is the mechanism: the amphoteric-attack and hydrogen-evolution account remains an interpretation from general chemistry and is labelled as one. Sprint 6 found the equivalent statement for sodium HYDROXIDE and correctly declined to carry it across; this is the carbonate-specific source that declining required.
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)
Verification: the work exists and is described correctly. Nobody has yet read the specific passage.
Last reviewed by a person on .
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
Why we say this
Supported
Labelled as interpretation because the wool body advises against heavy-duty detergents generically rather than naming sodium carbonate. The inference from 'avoid strongly alkaline products' to 'avoid this strongly alkaline product' is sound and is shown as an inference.
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. (cleaninghq's interpretation of what it says)
Verification: a person has read the passage relied on.
Read on — The detergent-selection guidance and its bleach and enzyme statements. Supports a wider statement — our claim was widened. CleaningHQ had recorded wool as bleach-sensitive with respect to CHLORINE bleach only, following the Sprint 1 verification target. Woolmark's position is wider, and the wool record, the oxygen-bleach agent record and the laundry relationships were all widened to advise against oxygen bleach on wool as well. Separately, because the page supplies no mechanism, CleaningHQ's keratin-hydrolysis explanation is now cited to this source as background only and rests on protein chemistry from elsewhere.
Kirk-Othmer Encyclopedia of Chemical Technology
John Wiley & Sons · Reference work
Relied on for: That alkaline hydrolysis degrades protein. (background and mechanism only)
Verification: the work exists and is described correctly. Nobody has yet read the specific passage.
Last reviewed by a person on .
Sodium carbonate may damage Painted and coated steel
Best avoided
The available guidance advises against this.
No longer an inference: a state hazardous substance fact sheet records that sodium hydroxide attacks coatings.
Precautions
- Wear gloves
- Wear eye protection
- Test on an inconspicuous area first
Why we say this
Supported
The fact sheet addresses sodium hydroxide rather than sodium carbonate, which is the weaker alkali, so this is recorded as avoid rather than unsafe and cites the stronger substance as the read evidence for the mechanism. Caustic oven and drain products contain hydroxide; washing soda does not.
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)
Verification: a person has read the passage relied on.
Read on — The hazard rating panel and the Reactivity section. RE-READ IN SPRINT 6 from the PDF itself for the reaction-with-metals statement. Supports a wider statement — our claim was widened. Clears the last safety-bearing citation in the catalogue that rested only on unread sources: the alkali-attacks-aluminium edge now cites a regulator whose passage was read. It also supplied two things CleaningHQ did not have — that the reaction generates flammable and explosive hydrogen gas, which is a hazard rather than merely cosmetic damage, and that sodium hydroxide attacks COATINGS, which is the first read source behind the painted-and-coated-steel record.
Last reviewed by a person on .
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.
Why we say this
Supported
Recorded as may damage rather than unsafe on because the source prohibits AGGRESSIVE alkaline cleaners without placing washing soda in that class by name.
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)
Verification: a person has read the passage relied on.
Read on — Read in full. Sections 3 General, 4.1 light surface soil, 4.3 organic coatings, and 5 Cleaning Precautions. Supports the claim as stated.
Last reviewed by a person on .
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.
Why we say this
Supported
The guide prohibits the pH class rather than a chemical. Recorded against the alkaline agent the catalogue holds; it is not a claim that the source tested washing soda.
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)
Verification: a person has read the passage relied on.
Read on — General care and cleaning instructions, basic and advanced cleaning technique, and the Suede section. Supports the claim as stated.
Last reviewed by a person on .
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
Sprint 29. A hot washing-soda soak, named for tannin staining specifically.
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.
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.
Verification: the work exists and is described correctly. Nobody has yet read the specific passage.
What CleaningHQ cannot answer yet
These are recorded questions about this subject that we have not yet researched to a standard we would publish.
- Compare surfactant and alkaline routes to grease removal
- Compatibility of alkaline degreasers with coatings
Last reviewed by a person on .