Cleaning with Oxalic Acid? Here’s What You Need to Know.

Oxalic Acid Uses

Oxalic Acid is a reliable & effective cleaner when used in appropriate applications. Oxalic Acid may be used to remove rust and other difficult stains from areas such as buildings, boats, swimming pools, concrete driveways, sidewalks, iron machinery, wood decks, stairs or trim. Oxalic also has a reputation for being an excellent wood bleach to restore stained, unfinished light woods to their natural color. If you’re thinking about cleaning with Oxalic Acid, here are some things you need to know.

How To Clean With Oxalic Acid

First, pre-clean the stained area by removing any dirt, grease, grime, or debris from the surface, possibly including the use of soap and hot water. When the stained area has been pre-cleaned, you will need to prepare an Oxalic Acid solution.

Oxalic comes in dry crystal form and is typically mixed with warm or hot water to bring it into a solution for cleaning. The solution can then be sprayed onto the stained area and scrubbed with a brush to remove stains. When cleaning with Oxalic, it may be necessary to let the product sit on the stain to be effective. Also, badly stained areas may need to be cleaned multiple times. After cleaning with an Oxalic Acid solution, rinse thoroughly with plenty of water and let the surface dry clean.

How much Oxalic Acid do you need to use? For maximum effectiveness, the ratio of Oxalic Acid to water will vary depending on the application it is used in. To get started, here are some suggestions:

  • For outdoor areas such as concrete driveways, sidewalks, and buildings, add one cup of Oxalic per gallon of warm water.
  • For wood applications, use two cups of acid crystals per gallon of hot water. Oxalic is effective at removing many types of stains in wood, including black water stains and weathering and tannin stains. Spread the solution out after applying to prevent uneven bleaching. After scrubbing, rinse the surface thoroughly until no white residue shows. If being used in a wood finishing application, make sure there is no white residue left before sanding.
  • For rust removal on metal machinery parts, first, pre-clean with soap and water to remove grease and grime. Metal parts may be soaked in a solution that is ten parts water to one part Oxalic. For soaking, it may be necessary to soak for up to a day to remove all the rust. Rinse and dry clean parts.

Do you have feedback on how you clean with Oxalic? We’d love to hear it!

How Oxalic Acid Works

Oxalic Acid is widely known for its ability to remove rust stains. How does Oxalic remove a stain that many other types of cleaning chemicals can’t budge? Here are the fascinating facts!

When Oxalic Acid comes in contact with rust, a chemical reaction known as a double displacement reaction occurs. This changes the rust (a.k.a. iron oxide) into iron oxalate. Since iron oxalate is a water-soluble salt, it dissolves in water and easily rinses away.

Basically, the iron in the rust attaches itself to the oxidized carbon in the acid to create iron oxalate, leaving the hydrogen and oxygen to get together to make some more…. water.

It looks like this:

Fe2O3 + 3H2C2O4 = Fe2(C2O4)3 + 3H2O

Iron Oxide (Rust) + Oxalic Acid = Iron(Iii) Oxalate + Water

(Cool, huh? And who knew that when you clean with Oxalic Acid more water is created in the process?)

Will Oxalic Acid Damage…?

While often used for cleaning, it is recommended you avoid prolonged exposure of Oxalic Acid to metals as it may lead to leaching of metal ions into solution.

Also, use caution about using in higher concentrations, as this may damage some surfaces (e.g. enameled cast iron). A better option may be to use a weaker solution several times.

Oxalic shouldn’t cause any damage to finishes it may incidentally come in contact with such as paint or varnish. When used in dilute amounts, it may also be used to clean galvanized metal or stainless steel. Rinsing your cleaning solution into the grass or other plants shouldn’t cause them any harm if you use plenty of water.

Wear Protective Equipment When Using Oxalic

When cleaning with this product, keep in mind that it is a strong acid and a poison. Wear protective clothing such as goggles and rubber gloves. Oxalic may cause skin irritation, and any skin that is exposed should be washed thoroughly after handling. When working with the dry crystals, take extra precaution to prevent inhalation or other internal exposure. For full safety information, review the safety data sheet.

Where To Buy Oxalic

You can buy Oxalic Acid in 55-pound bags online. Or, for smaller volumes, check your local hardware store for products labeled ‘wood bleach’ or ‘rust remover’.