Patio Cleaning Cardiff

Black spot removal, and why pressure alone will not shift it

Black spot is not dirt and it is not a stain. It is lichen, a slow growing organism that bonds into the top few millimetres of the stone. What you see as dots is only the visible part of it. The rest has worked into the pores of the slab, which is why it survives a wash that lifts everything else off.

Point a pressure washer at it and the result is predictable. The grime goes, the patio looks better for an afternoon, and the black spots are still there, now standing out more clearly against clean stone. Turning the pressure up does not solve it either. That erodes the slab around the lichen until the marks fade, and leaves a scoured surface that holds the next lot of growth better than the original did.

The method that works is chemical. Once the patio is washed and still clean, we apply a dedicated black spot remover and give it time to dwell. Product choice matters here. Some are sodium hypochlorite based, others are acidic, and an acidic one on limestone or on a lime rich concrete slab will etch the face and leave a chalky patch that cannot be reversed.

Be realistic about timing. The lichen is killed on the day, then the dead residue weathers and fades over the following two to six weeks, with rain and sunlight doing that part of the work. Badly colonised sandstone often needs a second application. A small number of very old, deeply pitted patios never come back perfectly clean, and we tell you that before you book rather than after.

The patio surfaces we clean

Riven Indian sandstone and pressed concrete can look almost identical under ten years of algae, and they want completely different treatment. So the first job on site is working out what you actually have. If we cannot tell from the face we look at a broken edge or lift a spare slab, because getting this wrong is what ruins patios.

• Indian sandstone. The patio we see most often in Cardiff gardens. It is the softest of the popular choices, layered, and porous enough to collect black spot faster than anything else we clean.
• Porcelain. Dense and close to non-porous. Lichen cannot root into it, so what looks like staining is usually surface film, grout haze left behind at installation, or algae sitting in the joints.
• Limestone. Acid sensitive. A cleaner meant for block paving can burn a pale chalky patch into limestone in seconds. Alkaline or hypochlorite based products and low pressure only.
• Slate. Thin layers that flake if you attack them. Very little pressure, a biocide and patience. A sealer afterwards brings the colour back out.
• Concrete slabs. On most pressed and wet cast slabs the colour sits in a thin pigmented face layer. Push too hard and you expose grey aggregate in patches, and there is no fixing that.
• Other natural stone. York stone flags off older Cardiff properties, granite, travertine and reclaimed paving all behave differently, so we test a hidden section first on anything we have not seen at your property.

Why a turbo nozzle never goes near soft sandstone

A turbo nozzle concentrates the machine's whole output into a spinning point. On concrete or hard block paving that is useful. On soft riven sandstone it works like a sander, leaving feathered edges, swirl marks and permanent striping wherever the operator's arm slowed down or sped up. It is the most common piece of DIY damage we get called out to look at, and no amount of washing puts it back.

We use a rotary flat surface cleaner instead. Two jets spin under a fixed height housing, so every part of the slab takes the same energy and nothing stripes. Pressure at the surface drops, coverage rises, and far less water is driven down into the joints. On very soft or very old stone we go gentler again, treat it chemically first, and use water mainly to rinse.

Joints, pointing and re-pointing

Most tired looking patios have a joint problem rather than a slab problem. Sand and cement pointing cracks as the base moves, water gets under it, frost lifts it, and by year five the joints are full of soil, moss and weed seed. Cleaning a patio in that state will take the loose material out, because it had already failed. Better to know that before the wash than to be surprised by it afterwards.

We show you which joints are going before any water goes down. Once the patio is clean and dry there are two routes. A brush-in jointing compound, which needs joints of a decent size, usually around 5mm wide and at least 25mm deep depending on the product, plus a dry spell to cure. Or raking out and re-pointing in mortar where the joints are too shallow for compound to hold. Either way, the joints get sorted before sealing, never after.

A considered patio cleaning process, start to finish

1. Survey and test patch. We identify the stone, check the joints and the fall of the patio, then clean a small area out of sight so you can see the real finish before we commit to the whole thing.
2. Protection. Borders, lawn edges, painted timber and planting within splash range are soaked with clean water and sheeted. Airbricks and door thresholds get checked, and we work away from the house so slurry does not run at the wall.
3. The wash. Rotary surface cleaner across the open area, hand work into edges, steps and around drain covers, all run in one direction so nothing shows up as a missed line once it dries.
4. Treatment. Black spot remover and biocide go onto the clean surface and are left to dwell. Ivy roots, deep moss and weed in the joints get dug out at this stage rather than washed over.
5. Joints and rinse. Joints are re-sanded, re-pointed, or left to dry ready for compound, depending on what we agreed. Then the patio, the path and any glass or render that caught overspray get a final rinse.
6. Sealing, if you want it. A separate visit after a run of dry days. Sealing damp stone is how patios end up milky, so we would rather come back than rush it.

Sealing, and when it is worth paying for

Sealer is not paint and it will not stop a patio getting dirty. An impregnating sealer soaks in and repels water and oil from inside the stone, so spills sit long enough to be wiped and algae has less to grip. A wet look sealer sits on the face and deepens the colour, which suits slate and sandstone and looks wrong on some concrete.

Two rules. The stone has to be genuinely dry, which in Cardiff means picking your week, and that means several dry days rather than one dry morning. And it has to be well past any black spot treatment so the chemistry has finished working. Seal damp stone and you trap moisture under a film that goes cloudy. Expect to reseal every two to four years on a patio in regular use. Porcelain does not need sealing, and we will say so rather than sell it to you.

What changes the price of patio cleaning

We price per job and fix the figure before we start. As a guide, a straightforward clean on a typical 20 to 40 square metre patio usually falls between £150 and £300. Black spot treatment adds roughly £2 to £4 per square metre, because the product is expensive. Sealing is the bigger addition, commonly £6 to £12 per square metre. Treat all of that as budgeting numbers rather than a quote, because the points below move it in both directions.

• Size and shape. A plain rectangle is quicker than the same area broken up by steps, planters and curves.
• How long it has been left. Two years of growth cleans in half the time of ten.
• The surface. Porcelain is quick. Pitted riven sandstone with lichen in every hollow is not.
• Access. Hoses run through a narrow side gate on a terrace in Canton or Roath, or gear carried through the house, is time on the job.
• Extras. Re-sanding, re-pointing, weed removal, sealing, and the steps or path you add once we are already there.
• Water and drainage. No outside tap, or a surface water gully already silted up, slows both setting up and clearing down.

Cardiff patios and the weather they live in

Cardiff gives lichen everything it wants. Wet winters, long damp spells and very little hard frost to knock growth back. North-facing patios and anything under mature tree cover go green fastest, which is why we do so much of this work in Penylan, Cyncoed, Lisvane and Roath. Older properties bring their own quirks: York stone flags bedded more or less straight onto soil, and paving tight against a Pennant sandstone wall that never dries out on the shaded side. We cover the rest of Cardiff as well, including Llanishen, Whitchurch, Rhiwbina, Radyr, Llandaff, Canton, Pontcanna, Grangetown, Splott, Rumney, Llanrumney and Cathays, plus Barry, Newport and the wider South Wales area.

Ready when you are: arrange your patio cleaning quote

Call or message 07576 128903 with a rough size and a photo of the worst corner, and we can usually give you a sensible idea of the cost straight away, then confirm it on site. Email is Liamdunn2406@outlook.com if that suits you better. We answer seven days a week, 7:00 to 21:30, we have been cleaning patios across Cardiff since 2019, and our Google rating is 5.0 from five reviews. Quotes are free and we do not charge to come and look.