Cleaning Porcelain Paving: What's Actually Different

Porcelain has become the default for new patios over the last decade, and almost everything written about cleaning natural stone is wrong for it.

The difference comes down to one property.

Porcelain is not porous

Outdoor porcelain is fired at very high temperature and vitrifies, meaning the material fuses into something close to glass. Water absorption is typically under 0.5%, and often under 0.1%.

Compare that with Indian sandstone at 1% to 6%.

Practically, nothing gets into porcelain. Not water, not algae spores, not stains, not sealer.

That single fact changes every part of how you look after it.

What that means for the good

Stains sit on top. Wine, oil, barbecue fat and leaf tannin cannot penetrate. Given reasonable promptness, almost anything comes off with detergent and a brush.

Algae cannot get into the material. Growth on porcelain is genuinely on the surface, so it lifts easily and does not recolonise from within the way it does on sandstone.

It stays clean far longer. A porcelain patio in the same position as a sandstone one will need cleaning perhaps half as often.

It takes more pressure safely. The body is extremely hard. You still need to be careful of the joints, but the slab itself is not going to erode.

What that means for the bad

Nothing soaks in, including sealer. Which is the point of the next section.

Surface film shows more. A dense, often matte or lightly textured surface shows a greasy film very clearly, and porcelain picks up film from barbecue smoke, from hard water, and from the wrong cleaning products. A patio that looks dull rather than dirty usually has a film on it rather than growth.

It gets slippery. Because algae sits on a smooth hard surface with nothing to key into, wet growth on porcelain can be more slippery than the same growth on riven sandstone. Check the slip rating of anything you are buying.

The joints are the weak point. All the durability is in the slab. The grout between them is ordinary cementitious material and it is what fails.

Do not seal porcelain

This is the main thing worth saying, and it is worth saying bluntly because it is sold constantly.

An impregnating sealer works by penetrating a porous material and lining the pore walls. Porcelain has effectively no pores. The sealer has nowhere to go.

What happens is that it sits on the surface, partly cures into a thin film, and then wears off unevenly in the traffic pattern over the following year. The patchy sheen you are left with is harder to remove than it was to apply.

If somebody quotes you for sealing a porcelain patio, ask them what the sealer is penetrating.

The grout is a different matter. Cementitious grout between porcelain slabs is porous and it does stain, and sealing that specifically is reasonable. Some installers do it as standard.

Grout haze

The most common complaint about new porcelain, and it is not dirt.

During installation a thin film of grout residue is left across the face of the slabs. It dries to a dull haze that people assume is dirt or a manufacturing fault. It is neither.

Water will not touch it. It needs a proprietary cement or grout haze remover, which is mildly acidic, applied and worked with a white pad and then rinsed thoroughly.

Do it soon. Fresh haze comes off readily. Two-year-old haze that has been walked on and weathered is considerably harder.

Test in a corner first. Some acidic products will attack the grout joints themselves if left too long.

The right way to clean it

A pressure wash at moderate pressure with a surface cleaner is fine on the slabs, and the constraint is the joints rather than the porcelain.

Keep the jet away from the grout lines, or at least keep the standoff up and the fan wide over them. Blowing out a grout joint on a porcelain patio is the one expensive mistake available here, because unlike sand it cannot be brushed back in.

For routine cleaning, honestly, a stiff brush, warm water and a little detergent does most of it. Porcelain is the one surface where the DIY answer is genuinely adequate most of the time.

Avoid anything strongly acidic on the joints and anything oily or waxy on the slabs, which is what leaves film.

What I charge

Porcelain is £4.50 a square metre, the same as concrete slabs. It is not slow work and there is no reason to charge more for it.

I will not quote you for sealing it, and if you have been quoted for that elsewhere, that is worth a second look.

The joints are the whole maintenance story

Because the slabs themselves are inert, everything that goes wrong with a porcelain patio over time happens in the joints.

Cracking. Porcelain is laid on a full mortar bed with a slurry primer, and the joints are grouted with a specific exterior porcelain grout. Where the bed was not full, or the primer was skipped, slabs flex slightly and the grout cracks. That is an installation fault showing up two winters later.

Staining. Cementitious grout is porous even where the slab is not, so the grout lines darken with algae and dirt long before the slabs do. This is what makes a porcelain patio look tired.

Blow-out from pressure washing. The single expensive mistake available. Sand can be brushed back into block paving. Grout cannot be brushed back into a porcelain joint. It has to be raked out and replaced properly.

So the rule on porcelain is: moderate pressure on the slabs, wide fan and long standoff anywhere near a joint, and never a turbo nozzle.

Sealing the grout, which is a real thing

Distinct from sealing the slabs, which is not.

An impregnating sealer applied to the grout lines reduces staining and makes them easier to clean. Some installers do it as part of the job.

It is worth doing on a light coloured grout, which shows everything. On a dark grey grout it makes very little visible difference.

Applied with a small brush or an applicator bottle along the joints, not flooded across the whole patio, because the slab will not absorb it and it will sit on the surface.

Slip resistance

Worth a paragraph because it is the one genuine safety consideration with porcelain.

External porcelain is sold with a slip rating, commonly expressed as an R value. R11 is the usual minimum for outdoor use in this country and R12 is better for anywhere that gets wet and shaded.

The problem is that the anti-slip performance comes from a surface texture, and that texture is what holds dirt. A textured porcelain slab that has gone green is more slippery than a smooth one that is clean, which is a slightly perverse outcome.

Keeping it clean is the answer, and porcelain makes that easy. A brush and detergent twice a year genuinely does it.

Routine care, which is genuinely simple

Sweep it. Wash it with warm water and a little washing-up liquid or a pH-neutral tile cleaner once or twice a year. Rinse it properly.

Avoid anything oily, waxy or with added shine, because it leaves film on a surface that cannot absorb it.

Avoid strong acids near the grout.

Deal with spills reasonably promptly, though there is little urgency because nothing soaks in.

That is the whole of it. Porcelain is the lowest maintenance patio surface available and the main risk to it is somebody treating it like sandstone.