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Hydrochloric acid

The strong mineral acid in brick acid and the harshest toilet cleaners. It attacks copper, brass and zinc, and meeting an oxidiser it gives off chlorine gas.

What not to do

These are the combinations an authority has warned about. A substance nobody has warned about has not been cleared, and none of this is permission to mix.

Never mix

Chlorine gas is released, and this is the strongest domestic version of the acid-and-bleach reaction because hydrochloric acid is the strongest acid a householder is likely to have. Chlorine causes coughing, chest tightness and shortness of breath, and its effects can be delayed by hours. Get well clear, do not go back in to ventilate, and seek medical advice even if breathing settles.

Read the full warning

Hydrochloric acid is unsafe on Anodised aluminium

Unsafe

Do not do this. The risk is established, and it is described below.

Precautions

  • Wear gloves
  • Wear eye protection
  • Ventilate the area

Evidence

Strongly supported

Sources

  1. AAMA 609 & 610-02: Cleaning and Maintenance Guide for Architecturally Finished Aluminum

    American Architectural Manufacturers Association (AAMA), 2002 · Standards body

    Relied on for: That cleaners containing hydrochloric acid must not be used on anodised surfaces. (states this directly)

Hydrochloric acid is unsafe on Copper and brass

Unsafe

Do not do this. The risk is established, and it is described below.

The reaction releases hydrogen, so this is a fire and explosion warning as well as a damage one.

Precautions

  • Ventilate the area
  • Wear gloves
  • Wear eye protection

Evidence

Strongly supported

Sources

  1. Right to Know Hazardous Substance Fact Sheet: Hydrogen Chloride (RTK 1012)

    New Jersey Department of Health, 2016 · Government or regulator

    Relied on for: That hydrogen chloride will attack many metals such as copper, brass and zinc to release flammable and explosive hydrogen gas. (states this directly)

Hydrochloric acid is unsafe on Stainless steel

Unsafe

Do not do this. The risk is established, and it is described below.

Precautions

  • Wear gloves
  • Wear eye protection

Evidence

Strongly supported

Sources

  1. Right to Know Hazardous Substance Fact Sheet: Hydrogen Chloride (RTK 1012)

    New Jersey Department of Health, 2016 · Government or regulator

    Relied on for: That hydrogen chloride corrodes steel. (states this directly)

  2. Care and Maintenance of Stainless Steel

    British Stainless Steel Association, Stainless Steel Advisory Service, 2001 · Trade or professional body

    Relied on for: That chlorides attack the passive layer on stainless steel and cause pitting corrosion. (states this directly)

Hydrochloric acid is unsafe on Polished marble

Unsafe

Do not do this. The risk is established, and it is described below.

Precautions

  • Wear gloves
  • Wear eye protection

Evidence

Strongly supported

Sources

  1. Cleaning & Maintenance Guidelines — Gardens & Driveways

    Marshalls plc · Manufacturer documentation

    Relied on for: That limestones and marbles must not be acid cleaned because hydrochloric acid dissolves them. (states this directly)

  2. Care & Cleaning of Natural Stone

    Natural Stone Institute · Trade or professional body

    Relied on for: That calcareous stone is sensitive to acidic solutions which may dull or etch it. (states this directly)

Hydrochloric acid is unsafe on Cement and mortar

Unsafe

Do not do this. The risk is established, and it is described below.

The joint dissolves faster than the deposit does, and joints do not grow back.

Evidence

Supported

Sources

  1. Cleaning & Maintenance Guidelines — Gardens & Driveways

    Marshalls plc · Manufacturer documentation

    Relied on for: That acid washing is material-dependent and that limestones and marbles are dissolved by hydrochloric acid. (inferred from the source; not stated directly)

Hydrochloric acid is unsafe on Sandstone

Best avoided

The available guidance advises against this.

Precautions

  • Test on an inconspicuous area first

Evidence

Supported

Sources

  1. Cleaning & Maintenance Guidelines — Gardens & Driveways

    Marshalls plc · Manufacturer documentation

    Relied on for: That sandstones vary under acid washing and that some turn orange because of their iron content. (states this directly)

Hydrochloric acid must never be mixed with Sodium hypochlorite (chlorine bleach)

Unsafe

Do not do this. The risk is established, and it is described below.

The strongest domestic version of the acid-and-bleach reaction, and an outdoor one, where people assume ventilation is not a concern.

Precautions

  • Never mix with other cleaning products
  • Ventilate the area
  • Wear gloves
  • Wear eye protection
  • Consider professional help

Evidence

Strongly supported

Sources

  1. Right to Know Hazardous Substance Fact Sheet: Hydrogen Chloride (RTK 1012)

    New Jersey Department of Health, 2016 · Government or regulator

    Relied on for: That hydrogen chloride reacts with oxidising agents including chlorine to form toxic chlorine gas. (states this directly)

  2. Dangers of Mixing Bleach with Cleaners

    Washington State Department of Health · Government or regulator

    Relied on for: That bleach must not be mixed with acidic products because toxic chlorine gas is produced. (states this directly)

Precautions

  • Never mix with other cleaning products
  • Ventilate the area
  • Wear gloves
  • Wear eye protection
  • Keep away from children and pets
  • Rinse thoroughly afterwards
  • Consider professional help

In detail

Hydrochloric acid is the strong mineral acid a domestic reader is most likely to encounter, usually under the name brick acid or in the harshest class of toilet-bowl cleaner, and the regulator's own list of uses includes metal pickling and cleaning and, stated plainly, household cleaners. It removes limescale, cement smears and mortar residue faster than any organic acid, and everything that makes it fast makes it dangerous to the surroundings. It corrodes steel, and it attacks many metals — copper, brass and zinc are named — releasing flammable hydrogen gas as it does so. That rules it out anywhere near plated taps, brass fittings, galvanised gutters or a boiler. Two further points decide most real questions about it. Reacting with an oxidising agent it forms chlorine gas, which is the same outcome as the bleach-and-acid accident approached from the acid side. And on any carbonate stone or cement-based grout it does not clean the surface, it dissolves it — the deposit and the substrate are chemically the same target.

Properties

Chemical name
Hydrogen chloride solution
pH
Strongly acidic

What works

Why

Sources for this page

Sources

  1. Right to Know Hazardous Substance Fact Sheet: Hydrogen Chloride (RTK 1012)

    New Jersey Department of Health, 2016 · Government or regulator

    Relied on for: That hydrogen chloride solution is hydrochloric acid, is used in metal cleaning and household cleaners, attacks copper, brass and zinc releasing hydrogen, corrodes steel, and forms toxic chlorine gas on reaction with oxidising agents. (states this directly)

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