5 min read
Why porcelain is different
External porcelain is fired to near-zero water absorption. Because it takes on almost no water, it is frost-proof, does not stain, and does not need the sealing that porous sandstone and limestone require. Wine, oil and barbecue fat sit on the surface rather than soaking in.
This changes what maintenance means. On natural stone you are protecting the material. On porcelain the material looks after itself and you are simply cleaning what lands on it — and looking after the joints between the slabs, which are mortar or resin and are not porcelain.
The routine
Sweep regularly, especially in autumn. Wet leaves left on paving are the main source of the organic film that algae then colonises, and the tannins in them can leave a temporary shadow.
Wash a few times a year with warm water, a little washing-up liquid or a pH-neutral hard-surface cleaner, and a stiff brush. Rinse properly — leaving detergent to dry on the surface leaves a film that attracts more dirt than it removed.
That is genuinely most of it. A porcelain terrace given a sweep through autumn and two proper washes a year will look close to new indefinitely.
Winter algae — the actual problem
The green film that makes paving slippery from November onwards is algae, and in a shaded, damp London garden it is a question of when rather than whether. It grows on the surface, not in it, so on porcelain it lifts off easily — but pressure alone only removes what is visible and it returns within months.
The fix is a proper biocide or patio cleaner applied and left to work for the stated time before washing off. That kills it at the root and buys most of a year. Doing this in late autumn, before the worst of the weather, is more effective than reacting in February.
Improving airflow and light helps as much as any chemical. Cutting back overhanging planting so the surface actually dries between showers reduces regrowth more than anything you can buy.
The joints are the weak point
Porcelain slabs are effectively indestructible. The mortar or resin between them is not, and it is where problems begin.
Look along the joints once a year. Hairline cracking or a section that has crumbled lets water get beneath the slab, and water under a slab in a hard frost is what lifts it. Small failures are easy to rake out and repoint; ignored, they become a lifted slab and a much bigger job.
If your patio was jointed with a brush-in resin compound, note that these have a service life and can go brittle after some years. Repointing a terrace is straightforward, far cheaper than relaying it, and worth doing before winter rather than after.
What not to do
Porcelain is hard to damage, but there are three reliable ways to manage it.
- Do not use acid-based cleaners
- Brick and patio acids will not hurt the porcelain but will attack the cement in the joints, and any splash onto adjacent natural stone, brick or metal will etch it permanently.
- Do not put a pressure washer close, or on a joint
- A lance held near the surface will blow jointing compound out and can drive water under the slabs. Keep the nozzle well back, use a wide fan or a rotary flat-surface head, and never aim directly into a joint.
- Do not use rock salt for ice
- The porcelain will cope, but salt is corrosive to mortar joints and to any nearby metal, and it damages planting when it washes into beds. Grit or sand gives grip without the chemistry.
- Do not drag metal furniture
- It will not scratch the porcelain, but it can leave grey metal transfer marks. These look alarming and come off with a cream cleaner and a little effort — but not dragging is easier.
Stains, if they happen
Most marks on porcelain are not stains at all — they are residue sitting on top. Work up from the mildest treatment: warm soapy water, then a pH-neutral cleaner, then a dedicated porcelain cleaner suited to whatever caused it.
Two specific cases. Grout haze, a cloudy film left after installation, needs a proprietary grout haze remover rather than more scrubbing. Rust marks from a metal planter or a dropped tool respond to a dedicated rust remover for tiles, and will not shift with anything general.
Because nothing penetrates the surface, patience with the right product beats force almost every time.
- Does porcelain paving need sealing?
- No. External porcelain absorbs almost no water, so there is nothing for a sealer to penetrate and nothing to protect against. Sealing it is at best a waste of money and at worst leaves a film that traps dirt. This is one of the main practical advantages over sandstone and limestone, which do benefit from sealing against oil and staining.
- Can I use a pressure washer on a porcelain patio?
- Yes, with care. The porcelain itself is unaffected, but the joints are not — a lance held close will strip jointing compound and can force water under the slabs. Use a wide fan or a rotary flat-surface attachment, keep the nozzle well back, and never aim into a joint. A brush and warm soapy water handles most routine cleaning without the risk.
- Why has my porcelain patio gone green?
- Algae, which grows on any surface that stays damp — very common in shaded London gardens through winter. It is sitting on the porcelain rather than in it, so it removes easily, but pressure alone only clears the visible growth and it returns. Apply a proper biocide, leave it the stated time, then wash off. Improving light and airflow so the surface dries between showers slows regrowth more than any product.