The Simple Soda Crystals and Washing-Up Liquid Patio Cleaning Trick from Fix it with Fowlers

Many people instinctively reach for a pressure washer or harsh DIY-store chemicals. A British DIYer shows there’s a much easier, quieter approach that’s kinder to the environment, pets and the stone itself: two everyday cupboard products, a bit of time, and a stiff scrubbing brush.

Why the patio looks so bad after winter

After months of rain, frost and weak sunshine, patio slabs often end up coated with a cocktail of algae, moss, lichen and ordinary road grime. If you leave metal garden furniture outside, you may also spot ugly rust rings around chair and table legs. Pale stones can quickly look blotchy and tired.

The common response is predictable: get the pressure washer out, add chemicals, and “blast everything off”. Over time, though, that approach can create fresh issues.

• The jet from a pressure washer can wash out jointing material and roughen the surface.
• Strong cleaners can attack pointing and some natural stones.
• Dirt may be removed, but the newly roughened surface can pick up grime again faster afterwards.

Quite a few people now rely on household standbys such as vinegar cleaner. It can help against limescale and some deposits, but it’s still an acid. On delicate stone it may leave fine etch marks that only show up later when the light hits at an angle. Soil organisms around the patio also don’t appreciate repeated acidic run-off.

"If you use high pressure and aggressive products every year, you’ll slowly destroy your patio while you clean it."

The simple two-product trick for clean slabs

The British DIY channel “Fix it with Fowlers” demonstrates an alternative that sounds almost too plain: a bag of soda crystals, a squirt of washing-up liquid, plus a scrubbing brush and a little patience. For many standard patios, that really is enough.

What soda crystals actually are

Soda crystals (also called washing soda) are an old-school household helper from the days before specialised cleaners. They’re an alkaline salt that cuts through grease and loosens organic dirt. Key point: this is not the same as bicarbonate of soda (the baking ingredient), and it’s certainly not the same as caustic drain cleaners based on sodium hydroxide.

• help break down greasy films and barbecue residues
• soften algae layers and general grime
• are far less aggressive than many specialist patio cleaners

Alongside that, you use ordinary washing-up liquid. In the kitchen it breaks down fats and oils so they rinse away more easily. Outdoors, it’s particularly useful for barbecue grease, soot and traffic-film dirt.

Step-by-step: how the method works

Preparation matters at least as much as the cleaning mix. If you simply pour something over the slabs, you’ll often end up annoyed by streaks later.

1. Clear the joints: Use a jointing scraper or a small spade to remove weeds and loose soil.
2. Sweep thoroughly: With a stiff broom, sweep away dust, sand and larger debris.
3. Dampen the slabs: Evenly wet the area using a garden hose or watering can.
4. Sprinkle soda crystals: Spread a thin layer over the wet surface-no need for thick piles.
5. Add washing-up liquid: Apply several thin lines or a few squirts across the slabs.
6. Scrub hard: Work it in with a stiff brush, including across the joints.

Then comes the slightly counter-intuitive part: don’t rinse straight away-leave it to do the work. The DIYer leaves the mix on the slabs for up to 48 hours before rinsing again with clean water. Over that period, part of the build-up loosens on its own.

"Give the cleaner time and you’ll save effort later-the patio comes up cleaner, without a noisy machine."

Safety and common mistakes when cleaning a patio

Soda crystals are considered relatively gentle for household use, but they are clearly alkaline. In other words, you don’t need to tip out half a kilo at once. For many domestic areas, a light sprinkling-or a bucket of hot water with a few tablespoons-can be perfectly adequate.

What homeowners should watch out for

• Avoid contact with eyes and skin: Short rubber gloves are a sensible precaution.
• Keep children and pets away: While the surface is wet, it’s best that nobody walks across it.
• Do a patch test: With sensitive natural stone, try an inconspicuous area first.
• Rinse well: After the dwell time, flush with plenty of water so no residue remains.

A frequent mistake is mixing multiple products-vinegar here, a chlorine cleaner there, maybe a stone cleaner as well. Random combinations can harm the stone and can also be dangerous to breathe if gases are produced. Stick to one method per pass and ensure good ventilation.

When a pressure washer still makes sense

If joints are heavily tarred, mud is baked on, or the coating is decades old, manual scrubbing may not shift it. In that case a pressure washer can help-used carefully:

• use a wide fan spray rather than a pinpoint jet
• increase the distance to the ground; don’t work right up close
• clean joints only at an angle and with reduced force
• renew jointing material afterwards if a lot has been washed out

If you pre-treat with soda crystals and washing-up liquid first, you often need far less pressure at the end because the dirt has already been loosened.

How to keep the patio clean for longer

Even the best cleaner won’t help much if everything turns green again a few weeks later. With a simple routine, the workload stays manageable.

Measure	Frequency	Benefit
Sweep with a stiff broom	every 1–2 weeks	Removes leaves and dust, reducing food for algae
Light clean with warm water and washing-up liquid	as needed, roughly monthly	Greasy films and fresh marks lift before they set
Two-product treatment with soda crystals	1–2 times per year	Deep clean before algae anchors itself
Move garden furniture	a few times per season	Prevents permanent shade areas and rust zones

If you schedule a lighter pass with soda crystals and washing-up liquid in autumn, spring usually starts much more smoothly. The typical black and green haze is often far less noticeable.

Which stones are suitable - and where to be cautious

This method is aimed mainly at common concrete slabs and many ceramic outdoor tiles. With natural stone, it’s worth taking a closer look:

• Concrete slabs: Usually fine, provided the joints aren’t already crumbling.
• Ceramic patio tiles: Generally unproblematic, but keep an eye on the joints.
• Sandstone, limestone, marble: Test a small area first and consider using a softer brush.
• Clay pavers: Often robust, but watch for efflorescence and colour changes.

Alkaline products such as soda crystals can, depending on concentration, roughen or discolour certain natural stones. In those cases, the safer option is a diluted bucket solution with a short dwell time, rather than sprinkling dry crystals and leaving them for two days.

More than just looks: the environment, pets and your budget

Getting the patio looking “like new” is only part of the appeal. By avoiding aggressive cleaners, you also protect whatever grows and lives around the slabs. A mix of soda crystals and washing-up liquid typically breaks down far better than specialist concrete chemicals, which can otherwise end up in drains or garden beds.

For pet owners, this is particularly relevant. Dogs and cats pad across wet paving and later lick their paws. A setup that avoids strong acids and chlorine-and, after thorough rinsing, doesn’t leave residues in puddles-reduces the risk considerably.

Cost matters too: soda crystals are only a few pounds per pack in supermarkets or chemists, and most people already have washing-up liquid at home. Compared with specialist cleaners-or buying a new pressure washer-this is kinder to the household budget, and to the neighbours who don’t want to listen to engine noise for hours on sunny weekends.