Washing soda strips algae, grease, and general grime off patios and decking without the fumes or plant-killing runoff that bleach carries, but only if you match the dilution and tools to the surface you're scrubbing.
- Washing soda (sodium carbonate) cuts through algae and oil-based stains on patios and decking without bleach's fumes — Buy for routine outdoor cleans in 2026.
- Skip it on unsealed natural stone and bare aluminium furniture; the alkalinity etches stone and pits aluminium.
- Pair washing soda with a stiff coconut-fibre brush, not a soft sponge, for real results on textured stone or grooved decking boards.
- Rinse thoroughly after use — washing soda left to dry can leave a chalky residue on dark composite decking.
Why this matters
Most patio and decking cleaners sold in the UK are either bleach-based, which yellows grass and kills plant roots on contact, or pressure-washer-only solutions that do nothing for the oily black algae film that builds up between wet spells. Washing soda sits in between: it's alkaline enough to break down grease, moss, and algae biofilm, but it doesn't chlorinate your soil the way bleach does. For anyone trying to keep a garden eco-friendly through 2026 without giving up a clean-looking patio, that trade-off matters.
Who this is for
This guide is for homeowners and renters who want a patio or decking area cleaned properly at least once a season without reaching for a bleach-based patio cleaner, and who already own or are willing to buy a decent scrub brush. If you're dealing with a sealed hardwood deck under a warranty that specifies approved cleaners only, check that paperwork first — washing soda is a general-purpose alkaline cleaner, not a manufacturer-approved product. A 7-piece kitchen cleaning brush set covers most of the scrubbing this job needs, from grout lines to decking grooves.
What to look for in washing soda for patios and decking
Purity of the sodium carbonate
Washing soda sold for laundry and household cleaning is sodium carbonate, and the cheaper supermarket tubs are usually just as pure as branded versions — you're not paying for a better chemical, you're paying for packaging. Check the ingredients list says sodium carbonate only, not a blend with surfactants or fragrance, since additives can leave streaking on stone.
Solubility in the water you'll actually use
Washing soda dissolves fully in warm to hot water but sits grainy in cold water, which matters outdoors where you're often filling a bucket from an outside tap. Warm the water on the hob or in a kettle first, or the granules will sit undissolved and scratch softer decking boards as you scrub.
Surface compatibility
Sealed hardwood decking, composite decking, and most natural stone (sandstone, slate, granite) tolerate washing soda diluted in water. Unsealed limestone and marble are the exception — the alkalinity can etch the surface over repeated use, so test an inconspicuous patch first.
The right application tool
Washing soda works as a chemical, but it needs mechanical scrubbing to shift ingrained algae and grease — spraying it on and walking away does very little. A stiff-bristled brush or a coconut-fibre scourer does the actual lifting; the soda just loosens what the bristles then remove.
Runoff and rinse-off
Washing soda raises the pH of whatever soil or grass it drains into, so keep runoff away from flower beds and lawns during application, and rinse the patio thoroughly with clean water once you're done. A short flush with a hose is usually enough to stop any residue drying into a white haze on dark composite boards.
Storage and reuse
Buy a size you'll actually get through — washing soda doesn't spoil quickly if kept dry, but a huge tub left open in a damp shed clumps and becomes harder to dissolve. A resealable, moisture-proof container beats a torn paper bag every time.
Top picks: the tools that make washing soda work
Washing soda itself is a commodity product you'll find in most UK supermarkets, so the real decision is what you scrub with. These are the tools that turn a tub of washing soda into an actual clean patio.
The scrub workhorse. The 7-piece kitchen cleaning brush set gives you seven differently shaped brushes, which covers everything from flat stone slabs to narrow decking grooves and grout lines in one purchase. For a patio with mixed surfaces, having more than one brush head on hand saves you switching techniques mid-clean. Buy if your patio has grout, edging, or decking grooves alongside flat stone.
The grease cutter. Coconut kitchen scourers are stiff enough to break up oily barbecue drips and bird mess on stone without scratching sealed surfaces the way steel wool does. They're built for kitchen grease, which is exactly the kind of stain washing soda struggles to lift on its own. Buy for patios that double as the barbecue zone.
The mixing and application tool. A refillable cleaning spray bottle in recycled aluminium lets you mix a washing soda solution and apply it evenly across vertical surfaces like decking balustrades or low garden walls, rather than sloshing a bucket over them. Consider it if your cleaning job includes upright surfaces, not just flat ground.
The budget alternative. Round coconut scourers, sold in packs of two, handle small, stubborn patches — a mossy corner, a single stained slab — without committing to a full brush set. They're not built for a full patio job on their own. Consider as a top-up buy, not your only tool.
What to avoid
- Bare aluminium furniture and trims. Washing soda's alkalinity reacts with untreated aluminium, leaving pitting and dark staining that doesn't come back out — keep it to stone, sealed wood, and composite decking only.
- Mixing it with vinegar or other acids. This looks like a stronger clean but actually neutralises both, giving you salty water with none of the cleaning power of either ingredient on its own.
- Skipping the rinse on dark composite decking. Washing soda left to dry on dark boards leaves a visible chalky film in direct sun — a full hose rinse straight after scrubbing avoids it entirely.
Verdict comparison
| Tool | Best for | Handles decking grooves | Verdict |
|---|---|---|---|
| 7-piece kitchen cleaning brush set | Mixed surfaces, grout, edging | Yes | Buy |
| Coconut kitchen scourers | Grease, BBQ stains, bird mess | Limited | Buy |
| Refillable spray bottle (recycled aluminium) | Vertical surfaces, balustrades | No | Consider |
| Round coconut scourers (2-pack) | Small stubborn patches | No | Consider |
Washing soda itself is a pH-11 alkaline that any UK supermarket stocks, so the tools above are what actually separates a mediocre clean from a proper one in 2026.
FAQ
Is washing soda safe for decking?
Washing soda is safe for sealed hardwood and composite decking when diluted in warm water and rinsed off fully afterward. It is not recommended for unsealed softwood, which can absorb the alkaline solution and discolour.
Can I use washing soda on natural stone patios?
Washing soda works on sandstone, slate, and granite, but can etch unsealed limestone or marble over repeated use. Test a small, hidden patch first before treating the whole patio.
How is washing soda different from baking soda for outdoor cleaning?
Washing soda (sodium carbonate) has a pH around 11 and is considerably more alkaline than baking soda (sodium bicarbonate), which sits closer to neutral. That makes washing soda better at cutting algae and grease, while baking soda is milder and better suited to gentle indoor jobs.
Does washing soda kill algae on patios?
Washing soda breaks down the biofilm that algae grows in, making it easier to scrub off with a stiff brush, rather than killing the algae outright like a biocide would. Combined with mechanical scrubbing, it removes visible algae effectively.
Will washing soda harm my grass or plants?
Washing soda runoff raises soil pH and can stress grass and plants if it drains into beds or lawns repeatedly. Keep runoff on hard surfaces and rinse it away from soil during application.
What's the best brush to use with washing soda on decking?
A stiff-bristled brush or coconut-fibre scourer does the mechanical work washing soda needs to lift grime, since the chemical alone does little without scrubbing. Soft sponges are not stiff enough for grooved decking boards.
Can washing soda be used on aluminium garden furniture?
No — washing soda reacts with untreated aluminium and causes pitting and dark staining that won't buff out. Stick to stone, sealed wood, and composite surfaces instead.
One last thing
The detail most people miss in 2026 is that washing soda needs warm water to actually dissolve — tip it straight into a bucket of cold tap water and you'll be scrubbing gritty, undissolved granules across your decking, which scratches softer boards rather than cleaning them. Warm the water first, dissolve fully, then scrub.
