Should you seal a sandstone patio in Hartlepool?

Why sandstone stains in the first place

Sandstone is made of sand grains cemented together, with tiny pores between them. Those pores give riven sandstone its natural texture and grip, but they also soak up whatever lands on them: rainwater, barbecue fat, red wine, leaf tannins and the spores of algae. In a damp, shaded corner, green growth gets a foothold quickly. The RHS explains that algae, mosses and lichens colonise hard surfaces that stay moist and shaded.

Hartlepool adds two local factors:

• Salt air. On the Headland and along the front at Seaton Carew, wind-blown spray reaches gardens regularly. Salt carried into porous stone can leave white marks as it dries out.
• Sea fret and shade. The Met Office notes that easterly winds often bring damp, dull conditions to the North East coast in spring and early summer. Patios in walled Headland yards, or under the big trees of the Park and Grange areas, may barely dry out for weeks.

What a sealer does, and what it does not

There are two broad types of stone sealer:

• Impregnating sealers soak into the pores and line them with a water-repellent layer, leaving the surface looking much the same. These are the ones we normally suggest for patios.
• Surface or "enhancing" sealers leave a film or deepen the colour, giving a wet look or a sheen. They change the appearance more, can wear unevenly in heavy-use areas, and on some products can make the surface smoother underfoot.

A sealer does:

• slow down how quickly liquids soak in, giving you time to wipe up spills
• make routine cleaning easier
• slow the build-up of green algae and black staining in many cases

A sealer does not:

• stop the stone weathering and changing colour over the years
• make the patio maintenance-free; it still needs sweeping and cleaning
• cure rocking slabs, poor drainage or failing joints
• last forever; most products need reapplying every few years, depending on wear and exposure

When we suggest sealing, and when we do not

Worth considering

• Pale stones such as buff or light grey, where staining shows most
• Dining and barbecue areas, where food and drink get spilt
• Shaded patios, under trees or in walled yards, where algae is a constant battle
• Gardens exposed to salt spray, on the Headland or the seafront

Often not needed

• Darker, multi-coloured stones, which hide weathering well
• Sunny, open gardens, such as many in Hart and on the estates around Throston, where the stone dries quickly after rain
• Owners who like a weathered look: unsealed sandstone mellows naturally, which suits older properties in the conservation areas

For porcelain, sealing is usually unnecessary because it absorbs so little water. If low maintenance matters most, our porcelain patios page explains the alternative.

Timing: do not seal too soon

A frequent sealing mistake is doing it too early. New patios are laid on a wet mortar bed, and as it dries, natural salts can be drawn up to the surface as white efflorescence. Sealing over it can trap the marks under the sealer. We suggest:

1. Let the patio settle and the mortar cure fully. Many sealer makers suggest waiting several weeks to a few months; follow the product guidance.
2. Wait for any efflorescence to appear and fade, helped by brushing and rain.
3. Clean the stone thoroughly and let it dry completely.
4. Choose a spell of dry, mild weather. On Hartlepool's coast that often means late spring or summer, and checking the forecast for fret.

How to seal a sandstone patio properly

1. Test first. Apply the sealer to a spare slab or a hidden corner and let it dry. Check the colour, the sheen and how it feels underfoot when wet.
2. Clean. Sweep, wash and remove any algae and stains. Sealer locks in whatever is on the surface.
3. Dry. The stone must be dry right through, not just on top.
4. Apply. Follow the manufacturer's coverage rate, usually with a brush, roller or low-pressure sprayer, working in sections. Do not let pools of sealer dry on the surface.
5. Keep off. Keep people and pets off for the drying time on the label.

Use the product safely: read the label, ventilate, wear gloves, and do not let excess sealer or cleaning solution run into outside drains, which carry rainwater to watercourses. GOV.UK's pollution prevention guidance explains why liquids should be kept out of surface water drains.

Keeping grip

A patio that has become slippery is worse than a stained one. The HSE explains that surface roughness is a key factor in how slippery a floor is when wet. Riven sandstone is naturally textured, so avoid any sealer that leaves a glossy film. If you are worried, the test slab will tell you.

Looking after sealed and unsealed stone

• Sweep regularly and clear leaves before they stain
• Wash with water and a stiff brush, and use cleaners suitable for natural stone
• Avoid acid cleaners on sandstone unless the manufacturer says they are safe
• Keep pressure washers at a distance and on a wide fan, or they can strip sealer and joints

If the joints are failing too, the patio may need re-pointing before sealing. Our Indian sandstone patios page covers laying and finishing natural stone.

Questions people ask