Soda Crystals: What They Are and How to Use Them

If you have ever wondered what your gran kept in that blue bag under the sink, this is probably it. Soda crystals are one of those quietly excellent British cleaning staples that most American cleaning guides skip entirely, because in the US the same product is harder to find on a supermarket shelf. Over here they sit in the cleaning aisle for a couple of pounds a kilo, and for greasy, grubby jobs they often outperform the trendier bicarb-and-vinegar routine.

This guide covers what they actually are, how they differ from the two things people muddle them up with, and a room-by-room list of what to use them on, with sensible metric doses.

What soda crystals actually are

Soda crystals are sodium carbonate, also sold as washing soda. They come as translucent crystals in 1kg or 1.5kg bags. Chemically they are a strong alkali, and that alkalinity is the whole point: alkalis break down fats, oils and greasy, protein-based grime, which is exactly the sort of mess that builds up around a kitchen.

They have been used for laundry and cleaning for well over a century. They are cheap, biodegradable, free from enzymes, phosphates and bleach, and fine to use in a home with a septic tank. One quirk worth knowing: they are a slightly "wet" product and can set rock hard in the bag, especially if stored somewhere warm. That does not spoil them. Break the lumps up, or dip the solid block in warm water and use the solution.

How they differ from bicarb and from oxygen bleach

People reach for three white powders and treat them as interchangeable. They are not.

Bicarbonate of soda (sodium bicarbonate, known as baking soda in the US) is a much gentler cousin. It is a fine powder and a mild alkali, good for deodorising, light scrubbing and jobs where you want something food-safe and non-scratching. Soda crystals are the coarser, far stronger relative: the same family, but with real degreasing muscle. As a rule of thumb, use bicarb for gentle and soda crystals for grease. Our full guide to cleaning with bicarbonate of soda covers where the gentler option shines.

Sodium percarbonate (oxygen bleach, the active ingredient in many "oxi" laundry boosters) is a different job altogether. When it hits warm water it releases hydrogen peroxide, which whitens and lifts stains and helps sanitise. Soda crystals do not bleach or whiten; they degrease and soften water. So for a greasy oven rack you want soda crystals, but for a dingy white shirt or a stained tea towel you want oxygen bleach. Some products, like a "laundry boost", combine soda crystals with a little oxygen bleach to do both.

Bicarbonate of soda	Soda crystals	Sodium percarbonate
Sodium bicarbonate (baking soda)	Sodium carbonate (washing soda)	Oxygen bleach
Mild alkali, fine powder	Strong alkali, coarse crystals	Releases hydrogen peroxide in warm water
Deodorising, light scrubbing, gentle jobs	Cutting grease, drains, laundry softening	Whitening, stain-lifting, sanitising
Gentle and food-safe	Degreaser, wear gloves	Best in warm or hot water
Not a disinfectant	Not a disinfectant	Has some sanitising action

Cutting grease: hobs, ovens, pans and extractor filters

This is where soda crystals earn their keep. The method is nearly always the same: dissolve them in hot water and let them soak. Heat and time do most of the work, so you can scrub less.

The soda crystals grease soak

1. 1

   Make a strong solution

   Dissolve roughly 250g of soda crystals in a bath, bucket or large container of hot water. For a sink-sized job, a couple of tablespoons in hot water is plenty. Always add the crystals to the water and stir until dissolved.

2. 2

   Submerge and soak

   Sink oven racks, grill pans, extractor (cooker hood) filters and greasy utensils in the solution. Give them at least an hour; leave really baked-on racks or pans overnight.

3. 3

   For flat surfaces, apply and wait

   For the inside of the oven or a greasy hob, wipe or spray on a strong solution, leave it to work for at least 30 minutes, then wipe off.

4. 4

   Wipe, rinse and dry

   The softened grease should wipe away with a cloth and far less scrubbing. Rinse everything with clean water afterwards, and dry metal to avoid water spots.

A few specifics from the same principle: for a burnt or scorched pan, fill it with hot water, stir in a couple of tablespoons of soda crystals and leave overnight, then lift off the softened residue in the morning (never do this in an aluminium pan). For chopping boards, mix a little warm water with soda crystals into a paste, scrub, and it lifts food stains and neutralises odours. For a barbecue, soak the grates in a strong degreasing solution just as you would oven shelves. Moral Fibres' popular homemade oven cleaner is essentially this idea thickened into a clinging gel, and it too warns to keep it off aluminium and to wear gloves.

Drains: dissolving grease and staying ahead of blockages

Most kitchen-sink blockages are grease and oil that has congealed as the waste water cooled, trapping food debris behind it. Because soda crystals are a strong alkali, they dissolve that fat. For a slow, greasy drain, pour a mugful of soda crystals into the plughole, follow with a kettle of very hot water, leave five minutes, then flush with more hot water and repeat until it runs freely. For maintenance, a mugful down each drain once a week keeps grease from building up in the first place, and they are safe with septic tanks.

They are best on grease and on slow drains rather than a pipe that is already solidly blocked, where a plunger, a drain snake or a plumber is the honest answer. Our guide to unblocking and cleaning drains naturally walks through the whole routine.

Laundry and the washing machine: a booster and water softener

In the wash, soda crystals do two useful things. First, a tablespoon added to your normal detergent helps shift greasy and organic stains, which is why they are handy for workwear, dog blankets and washable nappies. For stubborn stains, dissolve a strong solution in warm water and soak the item for an hour before washing as usual (a rough guide is one cup of soda crystals to about half a litre of warm water).

Second, in a hard-water area they act as a water softener. Soft water lets your detergent work harder, so you can drop to the soft-water dose on the box and save a little money. Dri-Pak suggests adding soda crystals by water hardness: about 25g for medium, 50g for hard and 75g for very hard water, put in the drawer if your detergent goes in the drum, or the other way round, so the two do not clump together.

There is an honest caveat here that a lot of cleaning sites gloss over. Soda crystals soften water by turning the dissolved calcium and magnesium into carbonate, and Good Housekeeping UK, quoting the Royal Society of Chemistry, notes that this carbonate is essentially limescale that still has to be flushed through. So treat soda crystals as a wash booster and softener, not a machine descaler: keep up a periodic empty hot maintenance wash with 300 to 500g of soda crystals in the drum, and in very hard-water areas alternate with citric acid to keep limescale down. Our guide to cleaning your washing machine naturally covers that routine. One thing they are not for is the dishwasher: do not tip soda crystals into a dishwasher (it needs proper dishwasher salt in its softener), and clean the dishwasher itself with white vinegar or citric acid instead.

Floors, tiles, patios and paths

A strong, hot soda crystals solution cuts through ground-in dirt and grease on hard floors and tiles, leaving them clean. The important caveat is that soda crystals strip wax and sealants, so do not use them on a waxed or oiled floor, on sealed or waxed wood, or on terracotta you want to keep sealed; for those, a little pure liquid soap in warm water is gentler.

Outdoors, soda crystals help clear moss and algae from patios, paths and drives. Sprinkle them over the growth and dampen with water; the moss dies back over a day or two, after which you sweep and rinse it away. Take real care not to let the solution run into flowerbeds or ponds, where it can harm plants and aquatic life, and test a hidden corner of a coloured or delicate patio first, as it can occasionally discolour some surfaces.

When to choose which

Match the product to the job and you will rarely go wrong. For grease and heavy grime, hobs, ovens, pans, extractor filters, greasy drains and greasy laundry, reach for soda crystals. For gentle deodorising and light scrubbing, or anything near food, reach for bicarbonate of soda. For whitening and stain removal on fabrics, reach for sodium percarbonate (oxygen bleach). And when you genuinely need to kill germs on a surface, none of these is a disinfectant, so use a product that is registered as one.