How to Clean a Patio with Soda Crystals and Washing‑Up Liquid

Many keen gardeners get a nasty surprise when spring arrives and they step onto the terrace: the slabs look dull, the joints have turned dark, and rusty rings appear around table legs. Instead of harsh chemicals or noisy machinery, a popular British DIY tip relies on two inexpensive cupboard staples - and avoids both vinegar and bleach entirely.

Why the terrace looks so dirty after winter

If you hardly go outside over winter, you often only notice the change once the sun comes out: what previously seemed “fine” suddenly looks like a problem area. There are straightforward reasons for this.

• Moisture: Rain and waterlogged ground keep paving damp for weeks - perfect conditions for algae and green film.
• Shade: Spots under tables and chairs, or close to the house wall, dry slowly, so lichens can spread.
• Temperature swings: Freezing and thawing draw grime into the tiniest pores.
• Metal furniture: Chair and table legs can leave rust marks and brown rings.

The result is a terrace that appears neglected even though the construction itself is absolutely sound. Many people instinctively reach for strong chemicals or a pressure washer - and over time that can do more harm than good.

Why pressure washers and vinegar are often a bad idea

A powerful jet of water is tempting because the dirt seems to disappear instantly. The downside is that the jet can strip away more than just grime - it can also remove material.

• Jointing material gets washed out and sand disappears from the gaps.
• The surface becomes rougher, meaning stones pick up dirt even faster in future.
• Spray splashes grime onto walls, windows and garden furniture.

Strong bottled cleaners can be just as troublesome. Bleach, harsh descalers or aggressive patio cleaners may attack joint mortar, can discolour natural stone, and often end up undiluted in borders or on the lawn.

Vinegar is often described as a “natural” household remedy, but chemically it is still an acid. With delicate stone such as limestone or sandstone, it can etch the surface. It also shifts the soil pH around the terrace and can put stress on plants and the life in the soil.

"The better solution avoids acids and high pressure - and instead uses two classic cleaning products that have been in many homes for years."

The two simple products that get slabs properly clean

The method popularised by a British DIY creator uses a straightforward pairing: soda crystals and ordinary washing-up liquid. Both are low-cost, easy to measure out, and generally much gentler for the garden and pets than many specialist cleaners.

What soda crystals do

Soda crystals, also known as washing soda, are traditionally used for laundry care. They cut through grease, loosen dirt, and help lift organic residues from hard surfaces. Those same qualities translate well to terrace slabs:

• break down baked-on grime and old barbecue grease
• help shift green film
• soften dark deposits trapped in the pores of the stone

Important: washing soda is not the same as sodium hydroxide (caustic soda). Caustic soda is far more aggressive and is unsuitable for domestic patio cleaning.

Why washing-up liquid is part of the mix

Washing-up liquid is a familiar kitchen staple: it removes grease and helps water carry dirt away more effectively. On a terrace it delivers three key benefits:

• greasy marks from barbecues, oil or wooden tables come away more easily
• fine road dust and soot lift better from the stone
• the foam spreads the soda solution more evenly

A basic, colourless washing-up liquid without bleach is completely sufficient. If you prioritise sustainability, choose one with an eco label.

How to clean it step by step

For a proper spring clean you do not need specialist kit. A sturdy brush, a bucket and a garden hose are enough - everything else comes from the cupboard.

1. Clear out the joints
   Use a joint scraper or narrow filling knife to remove weeds and loose soil from the gaps. This boosts the mix’s effectiveness and helps prevent regrowth.
2. Sweep the area thoroughly
   With a stiff outdoor broom, remove leaves, loose dirt and sand. That way the cleaning mix can work directly on the paving and surface film.
3. Dampen the slabs
   Hose down the terrace well so the soda crystals dissolve more quickly and do not blow away.
4. Scatter the soda
   Sprinkle the crystals lightly over the damp area - not in piles, but as a thin, even layer.
5. Add the washing-up liquid
   Squeeze a line of washing-up liquid across the surface. Do not overdo it, or it will foam excessively without improving the clean.
6. Scrub in
   Work the mixture firmly into the slabs and joints using a stiff brush. Move in sections so you do not miss any areas.

Afterwards, leave the solution on the surface for around 48 hours. During this period, deposits loosen and the film gradually breaks down. Then it is usually enough to rinse again with the garden hose to wash away the lifted grime.

"The mix of washing soda and washing-up liquid works slowly, but it is gentle on materials - ideal for older terraces, shaky joints and gardens with children or pets."

Safety, material compatibility and common mistakes

Even though these two products are relatively mild, a bit of care is still sensible.

• Avoid skin contact: Soda is mildly degreasing. Gloves help protect skin and nails.
• Keep children and pets away: While the area is wet, children and animals should not walk over it.
• Rinse well afterwards: Once the dwell time is up, rinse thoroughly with clean water so no puddles of residue remain.

Sensitive natural stones can react differently from concrete slabs or brick pavers. On pale, high-quality stone, it is worth testing in a discreet corner first. In that case, begin with less soda, more water and a softer brush.

Common errors that reduce effectiveness or cause damage include:

• overly concentrated cleaners (bleach, strong descalers)
• metal brushes that scratch the surface
• frequent use of a pressure washer set too powerfully

How to keep the terrace cleaner for longer

Once the deep clean is done, a light maintenance routine is usually enough to keep things looking good. No one wants a major cleaning session every few weeks.

Interval	Measure
every 2–3 weeks	sweep thoroughly with a broom, removing leaves and soil
when greasy marks appear	apply washing-up liquid in water locally and scrub with a brush
once each autumn	use a diluted soda–washing-up liquid mix to disrupt green film before winter

If you also lift furniture in autumn, use protective feet, and check metal parts occasionally, rust staining is reduced noticeably. Plant pots that drip should sit on feet or rollers, which helps prevent brown edges caused by standing moisture and fertiliser.

When a pressure washer can still make sense

If you are dealing with thick, compacted mud or decades-old dirt, brushes and household solutions can reach their limits. In that case, a pressure washer set moderately can help - provided you follow some ground rules:

• keep a distance of 20–30 centimetres
• lower the pressure and avoid turbo nozzles
• do not aim directly into joints and edges

Often it is enough to open up heavily clogged areas briefly with pressure and then follow up using the soda-and-washing-up-liquid approach. That keeps material loss under control.

What is really behind green film and rust stains

Many terrace owners casually call any green growth “moss”. In reality it is often algae or a thin film of microorganisms living on constantly damp stone. They need only light, moisture and a little nutrient dust from the air.

Rust marks usually come from metal feet, screws or decorative fittings. Dissolved rust particles settle into the pores and are difficult to remove with scrubbing alone. The mildly alkaline action of washing soda helps loosen these deposits without etching the stone.

With that background in mind, you can respond more precisely: sweep shaded areas more often, avoid leaving water standing on the slabs, and fit furniture with glides or coasters. Combined with the two-product clean, this is usually enough to keep a terrace looking presentable for many years - without harsh chemicals and without the constant noise of a pressure washer.