How to Clean and Seal Indian Sandstone to Have a Beautiful Patio

Indian sandstone is one of the most rewarding paving materials you can choose for a British garden, but it's also one that separates into two very distinct groups of owners: those who maintain it properly and have a patio that looks beautiful and characterful after twenty years, and those who don't maintain it and have a patio that looks like something discovered behind an abandoned Victorian greenhouse.

The difference between these two outcomes is not complicated work or expensive products. It's knowledge — understanding what the stone needs, when it needs it, and how to do it correctly. Once you have that knowledge, maintaining Indian sandstone is a modest annual commitment that delivers dramatic results in the long-term appearance of your garden.

This is the complete guide.

Understanding Why Sandstone Needs Maintenance

The starting point is understanding what sandstone actually is at a physical level, because this explains every maintenance requirement.

Indian sandstone is a sedimentary rock with a porous structure. Within that structure are microscopic channels — pores — that are open to the surface. In a dry environment, these pores do nothing problematic. In a wet British garden, these pores can admit water (which can freeze in winter and cause surface damage), oils and staining liquids (which penetrate and cause permanent discolouration), and biological organisms — algae, moss, and lichen spores (which colonise the stone surface and create both aesthetic and safety problems).

Sealing the stone with a quality impregnating sealant fills and seals these pores from within. The sealant molecules (typically silane-siloxane or fluoropolymer chemistry) migrate into the pore structure of the stone and create a hydrophobic barrier that prevents liquids from penetrating. The stone doesn't look different from the surface — it doesn't create a coating or sheen — but it now repels water and stains rather than absorbing them.

This is why sealing is so effective and why failing to seal leads to the problems described above.

Your Annual Maintenance Calendar

The maintenance requirements of Indian sandstone are modest and can be structured into a simple annual routine.

Every 2–4 weeks (or as needed): Routine sweeping to remove loose debris — leaves, grit, dirt. This is not about aesthetics alone; organic material left on the stone surface holds moisture and provides substrate for biological growth. Sweeping keeps the surface clean and reduces the conditions that biological growth needs.

Two to three times per year: A thorough wash-down with warm water and a stiff bristle brush. Add a small amount of pH-neutral stone cleaner or even dish soap to the wash water. Scrub systematically across the entire surface, rinse with clean water, and allow to dry fully. This removes accumulated grime, light biological film, and surface deposits before they become harder to shift.

Annually (ideally autumn, after the warmest weather): Full clean and sealant check. This is the main annual maintenance event:

1. Thoroughly clean the stone using a pH-neutral stone cleaner or, if biological growth is present, a proprietary biocidal stone cleaner.
2. Allow the stone to dry completely — at least 48 hours of dry weather, ideally longer.
3. Check the sealant condition: pour a small amount of water on the surface. If it beads into droplets and runs off, the sealant is performing. If it immediately soaks in and darkens the stone, the sealant has worn out and needs reapplication.
4. If resealing is required: apply impregnating sealant with a flat brush or roller, working it into the surface methodically. Remove any excess before it dries. Allow the full curing time specified by the sealant manufacturer before the surface gets wet.

The full maintenance protocol is documented on our maintenance page.

Cleaning Methods and Products: What Works

For routine cleaning and light staining: Warm water and a stiff nylon brush (never wire — wire can damage softer stone surface layers). For slightly more stubborn marks, a pH-neutral stone cleaner dissolved in the wash water. Products specifically formulated for natural stone are available from stone and tile suppliers. Alternatively, diluted dish soap is gentle enough for routine cleaning.

For biological growth (algae, moss, lichen): Proprietary biocidal cleaners designed for natural stone are the most effective solution. These contain active biocides that kill biological growth chemically, which then allow it to be scrubbed away. Apply according to the manufacturer's instructions — usually applied, left to dwell for 30–60 minutes, then scrubbed and rinsed. In severe cases, more than one treatment may be required.

Diluted bleach (approximately 1 part bleach to 10 parts water) is an effective DIY alternative for algae and moss, though it requires very thorough rinsing and should not be used near planted areas. Bleach at high concentrations can affect some stone colours.

For oil and grease stains (barbecue, oil drips): If fresh: cover immediately with an absorbent material (cat litter is excellent, or specialist stone poultice powder) to absorb the oil before it penetrates deeply. Leave for several hours, sweep away, then wash. For old, set oil stains: a proprietary poultice treatment — absorbent powder mixed with a solvent, applied as a thick paste, left overnight and removed — is the professional approach.

For rust stains (from iron garden furniture): A proprietary rust remover formulated specifically for natural stone. Standard rust removers for metal often contain acids that will damage stone. Always use stone-specific products. Prevention is better: avoid leaving metal furniture or fittings directly on unsealed stone.

What NOT to use on Indian sandstone:

• Acid-based cleaners: Many commercial patio cleaners contain hydrochloric or phosphoric acid. These acids chemically attack sandstone and limestone, dissolving the calcium carbonate in the stone and leaving permanent dull etching. Always read the label. If the product says "suitable for concrete or block paving" it may be acidic. If it says "suitable for natural stone" it should be pH-neutral, but verify.
• High-pressure washing on high settings: Concentrated jet washing can erode the surface of softer sandstones, blast jointing sand out of open joints, and force water under the bedding. A wide-fan pressure washer setting at moderate pressure is fine. A pencil-jet directed at stone or joints is not.
• Wire brushes: Scratch and score stone surfaces, leaving marks that don't wash out.

Choosing the Right Sealant

Two main types of impregnating sealant are appropriate for Indian sandstone:

Invisible/natural finish sealant: This protects the stone without altering its appearance — the stone looks exactly as it does unsealed (when dry) but now repels water and stains. This is the choice if you love the existing colour and tone of your stone.

Enhancing sealant: This protects the stone AND deepens and enriches the colour — producing an effect similar to how the stone looks when wet, permanently. For stones like Raj Green (whose complex olive and green tones become even more complex and vivid when enhanced) and Kandla Grey (whose cooler tones become richer), an enhancing sealant is genuinely transformative.

When in doubt, test on an inconspicuous area first — the effect is permanent until the sealant eventually wears and is reapplied.

Dealing With Specific Problem Scenarios

Neglected sandstone that hasn't been maintained for years: A deep clean is required before any sealing. Remove all biological growth with biocidal cleaner, allowing adequate dwell time and thoroughly scrubbing. Rinse thoroughly. Allow to dry completely — at least 72 hours. Then apply sealant. In severe cases, two applications of biocidal cleaner may be needed, with the stone allowed to weather between them.

Staining around BBQ area: The combination of grease, carbonised food, and ash creates complex staining. A degreaser designed for natural stone, combined with a fine-bristle scrubbing brush and warm water, handles most cooking-related stains if treated reasonably promptly. Seal the area particularly well before BBQ season.

Moss or algae in joints: A long-handled grout rake or old screwdriver removes established growth physically. Follow with biocidal treatment, allow to dry, and regrout with fresh jointing compound.

Browse our Indian sandstone collection — all products, from Kandla Grey to Mint Fossil to Rippon Buff — reward proper maintenance with decades of genuine beauty.

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