Washing soda: what it cleans and what it damages

Step by step

1. 1

   Check the care label

   Use washing soda only on washable cottons, linens and synthetics. Leave out anything made of wool or silk.

   Why: Strong alkalis damage protein fibers like wool and silk.

2. 2

   Put on waterproof gloves

   Wear gloves while measuring and handling the powder, and avoid breathing the dust.

   Why: It's a very strong alkali that irritates skin and causes serious eye irritation.

3. 3

   Measure ½ cup per load

   For a load of heavily soiled clothes, measure ½ cup of washing soda, the amount the Vermont Department of Health recipe uses.

   Why: Enough alkali raises and holds the pH of the wash water, which is where its cleaning power comes from.

4. 4

   Add it to the wash with detergent

   Add the washing soda along with your usual detergent and wash as the care label directs.

   Why: Washing soda is a builder, not a detergent: it softens the water and conditions the soil so the detergent's surfactants work better.

5. 5

   Check stains before drying

   Look over greasy spots after washing. Pretreat and rewash any that remain instead of drying them.

   Why: Heat from the dryer can set leftover grease.

What washing soda is and how it cleans

Washing soda is sodium carbonate, sometimes sold as sal soda. It's a strong alkali, much stronger than baking soda (sodium bicarbonate), and it's already a major ingredient in many laundry detergents: roughly 5 to 30% of traditional and high-density powders, according to a detergency review by Hubbe and colleagues.

It cleans in three ways. It raises and buffers the pH of the wash water. At that higher pH, insoluble calcium soaps of fatty acids, a common greasy soil, are converted into soluble sodium salts, a form of saponification. It also gives soil particles a negative charge so they release from fibers. And as a builder, it softens the water so the detergent isn't used up by hardness minerals.

It's also part of powdered oxygen bleach: sodium percarbonate splits into hydrogen peroxide and washing soda when it dissolves.

What washing soda is good for, and what it damages

Good for:

• Heavily soiled and greasy laundry. The Vermont Department of Health adds ½ cup to boost cleaning and calls it a strong grease cutter, which makes it useful alongside pretreating grease stains.
• Beverage spills on brick, concrete and stone other than marble or terrazzo. Georgia's extension uses 1 teaspoon of washing soda (or all-purpose laundry detergent) in 1 quart of warm water.

Damages:

• Aluminum. Alkalies darken and corrode it, so don't soak aluminum pans or use an aluminum bucket.
• Wool and silk. Strong alkalis harm protein fibers.
• Paint and some finishes. An older Michigan State bulletin warns that strong alkali solutions can remove paint.
• Skin and eyes. It's an eye irritant, and Georgia's guidance says to wear waterproof gloves.

How much to use, and what not to mix

• Laundry booster: ½ cup per load of heavily soiled clothes.
• Beverage spill on masonry: 1 teaspoon per quart of warm water.

Acids cancel it out. Mixing washing soda with white vinegar or citric acid produces a fizz of carbon dioxide as the acid and alkali neutralize each other, and what's left cleans less well than either one alone. Use them separately if you use them at all.

Chlorine bleach: the sources reviewed document no specific hazardous gas from washing soda and bleach, but the standing rule is to dilute bleach only with plain water and never combine it with other products in a container. See never mix these cleaners.

By situation

Greasy work clothes or kitchen towels

Pretreat the worst spots, then wash with your detergent plus ½ cup of washing soda.

A drink spilled on a brick or concrete patio

Mix 1 teaspoon of washing soda in a quart of warm water and sponge it on, then rinse with clean water. Don't use it on marble or terrazzo.

Wool sweaters and silk

Leave washing soda out of the load entirely and follow the care label instead.

Aluminum pans, trim or tubs

Keep washing soda solutions away from aluminum. The alkali can darken or corrode the metal.

Washing soda or baking soda

They aren't interchangeable. Baking soda is a mild alkali; washing soda is far stronger, which makes it better at cutting grease and much more likely to damage aluminum, wool, silk and skin.

What not to do

• Don't handle it bare-handed. It's a very strong alkali that irritates skin, and the powder causes serious eye irritation.
• Don't use it on wool or silk. Strong alkalis damage protein fibers.
• Don't use it on aluminum. Alkalies darken and corrode aluminum.
• Don't mix it with vinegar or citric acid. The acid and alkali neutralize each other, so the mixture cleans less well than either one alone.
• Don't use strong solutions on painted surfaces. Strong alkali solutions can remove paint.

Other methods that work

Baking soda

A much milder alkali, for jobs where washing soda would be too harsh.

Heavy-duty liquid detergent as a pretreatment

For a single greasy spot, rubbing detergent straight into the stain targets it directly, and washing soda can then boost the main wash.

Stain still there?

Greasy stains survived the wash

Washing soda boosts the whole load but doesn't target a spot. Pretreat the stain directly, then rewash with washing soda.

An aluminum item turned dark

That's the alkali reacting with the metal. Keep washing soda away from aluminum in the future.

Your hands feel dry or irritated

Rinse them well with water and wear waterproof gloves the next time you handle it.

Safety

• Washing soda causes serious eye irritation, and its dust can irritate airways. Rinse eyes with plenty of water if it gets in.
• Wear waterproof gloves and keep it out of reach of children.

Never mix cleaning products; see chemicals you must never combine.

Questions

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