Block Paving Cleaning and Sealing Cardiff

What the clean actually takes off

Block paving collects a predictable set of problems in South Wales. Road silt and roof grit settle into the joints and turn greasy. Moss roots in that. North-facing driveways in Llanishen, Rhiwbina and Lisvane grow black spot lichen, the flat tar-coloured discs that a jet washer will not shift no matter how long you stand there. Then there is tyre rub in the turning area, engine oil where the car sits, and leaf tannin under the limes and sycamores on the older streets. We pre-treat the lichen and give it dwell time, then clean with a rotary surface cleaner rather than waving an open lance about. The lance comes out afterwards for edges, kerbs and gullies.

Joint sand is structural, not decorative

A block driveway is not glued down. The blocks sit on a screeded bed of sharp sand over a compacted sub-base, and the whole thing works by interlock. Each block leans on its neighbours through the sand in the 2 to 5mm joint, and that sand passes the weight of your car sideways instead of letting it punch down through one block. Empty the joints and leave them empty, and blocks start to rock, top edges chip, wheel tracks appear where you turn in, and water runs down the sides of the blocks into the bedding layer. That is how a driveway ends up rutted. Plenty of Cardiff front gardens were converted to parking on a thin sub-base, so those joints are doing even more work than they should. Every clean takes joint sand out, so re-sanding is not an upsell. It is part of the job.

Kiln dried sand, and why builders' sand is the wrong answer

Kiln dried sand is silica sand, washed, graded to a tight particle size and dried until it holds almost no moisture. Bone dry sand pours like a liquid and reaches the bottom of the joint. Damp builders' sand clumps, bridges near the top and leaves a void underneath, and the silt in it is exactly what moss and weed seed feed on. We carry it sealed and keep it covered on site, because a bag left open in a Cardiff front garden for one wet afternoon is no longer kiln dried sand.

• It goes in dry, onto dry paving. Sanding a damp driveway wastes the sand and your money.
• We brush it across the whole area, then vibrate or re-brush it so it packs down instead of sitting loose.
• Sand settles. We top the joints up before we leave, and expect to add a little yourself in the first year.
• Joints should finish flush with the top chamfer of the block, not heaped and not 10mm down.
• Permeable paving is the exception. It is built to drain through its joints, so it takes clean angular grit of roughly 2 to 6mm, never fine kiln dried sand.

Block paving cleaning and sealing in Cardiff, step by step

1. Survey and pre-treatment. We walk the driveway with you. Rocking blocks, failed edge kerbs, oil patches, black spot and any previous sealer all change the plan and the price. Organic staining is treated and left to dwell before water goes on.
2. Deep clean and rinse. A rotary surface cleaner running at around 200 bar, in overlapping passes at a speed the blocks can take, then a lance pass on edges, steps and drainage. The slurry that comes off sets hard in a gully, so we flush it out and collect the arisings.
3. Dry out and put right. The paving needs 24 to 48 hours of dry weather. In that window we reset rocking blocks, re-bed loose edging and work on oil marks. There is no sense sealing over a block that is going to move.
4. Re-sand. Kiln dried sand brushed and vibrated into every joint to full depth, then topped up until the joints stop taking it. On a badly stripped driveway that means two or three passes.
5. Seal. Applied to dry paving with a dry forecast, normally in two coats, sprayed and back-rolled or brushed depending on the product. The second coat goes on once the first has taken, and we mask the house wall, the kerb line and anything else that should not carry a shine.

Sealer types: matt, satin, wet look and colour enhancing

There is no best sealer, only the right one for your blocks and the look you are after. Most driveway sealers are acrylic. Solvent based versions soak in further, bind the joint sand harder and darken the colour more. Water based versions smell far less and stay closer to the natural tone. Both want the same thing from the weather. Ask to see samples on your own paving in daylight before you choose, because a block that reads charcoal in a brochure can come up almost black under a wet look coat.

• Matt. Almost invisible. The paving looks like it does on a dry day, with no shine. The most forgiving finish, because uneven application does not show.
• Satin. A low sheen that lifts the colour without looking wet. The middle ground, and where most people land.
• Wet look. Gloss. The paving looks permanently freshly rained on and the colour goes much deeper. On the sloping frontages around Penylan and Cyncoed, ask for an anti-slip additive in the top coat.
• Colour enhancing. Brings back depth in blocks faded by years of UV. It is not paint, and it will not restore a block whose face has already worn away.

What sealing does, and what it does not do

• It binds the top of the joint sand, so heavy rain stops washing it out of the joints.
• It slows staining. Oil, barbecue fat and leaf tannin sit on the film instead of soaking in, which buys you time to lift them.
• It slows moss and algae coming back, and makes the yearly wash down much gentler.
• It holds colour, slowing the fade that turns red blocks pink and charcoal blocks grey.
• It does not stop weeds completely. Airborne seed roots in surface debris, sealed or not, so sweeping still matters.
• It does not fix a failed sub-base. Ruts, dips and rocking blocks are a laying fault and no coating holds them still.
• It does not permanently prevent efflorescence, and applied at the wrong moment it makes efflorescence far worse.
• It is not a repair for flaking blocks. A sealer glues a loose face down for a season, then comes away with it.

Cure time and the weather window

Sealer needs dry paving and a dry forecast, which in Cardiff is the whole problem. After a wash the blocks need 24 to 48 hours of decent weather to dry through, and longer on a shaded frontage that catches an hour of sun. Once it is on, most products are touch dry in one to three hours, walkable the same evening and driveable after 24 to 48 hours, with full cure taking up to about a week. Rain in the first few hours is the failure mode. Water landing on a part cured film blushes it white, and the fix is stripping it off and starting again. Below about 8 degrees Celsius the film will not form properly either, and on a cold frontage the surface sits colder than the air. In practice the sealing season here runs April to September, and we work off the forecast rather than the calendar.

Efflorescence, the white bloom on new paving

Efflorescence is a white powdery haze that comes out of the concrete itself. Free lime inside the block dissolves in moisture, wicks to the face and reacts with the air, drying there as a white salt deposit. It is not dirt and it is not a cleaning failure. It is worst on paving in its first year or two, and rain usually weathers it off over a few seasons. It matters here for one reason. Sealing over active efflorescence traps the salts under the film and leaves the driveway permanently milky. On young paving we check for it, then either treat and rinse it thoroughly before sealing, or tell you to give it another season.

When we will tell you not to seal

Sealing is not right for every surface, and we would rather say so at the quote than take the money. We advise against it on paving under about a year old, on paving still throwing efflorescence, and on blocks whose faces are already flaking. Permeable paving is meant to drain through its joints, so a film sealer works against the drainage the driveway was built for. Paving previously sealed with an unknown product needs a test patch, because incompatible sealers can lift or wrinkle. And if there is standing water, rutting or a dropped section, the sub-base comes first. Sealing that driveway just gives you a smart looking dip. In those cases we clean and re-sand, which on its own transforms most paving, and we revisit sealing another year.

How often block paving needs re-sealing

Two to four years is realistic on a domestic driveway. A frontage taking three cars a day will not hold like a patio with a table and chairs on it, and the strip where you swing the wheel to line up with the gate always goes first. Shaded frontages green over faster than open sunny ones. There is a simple test. Tip a bucket of water onto the worn part. If it beads and sits, the sealer is still working. If it darkens the block and soaks straight in, the film has gone. Caught at that point, a re-seal is a wash, a sand top-up and usually a single coat. Leave it seven years and you are back to the full job.

Ready when you are: arrange your block paving cleaning & sealing quote

We have been cleaning driveways and patios across Cardiff since 2019 and hold a 5.0 rating from 5 Google reviews. Our unit is in Cardiff, so most of the city is a short run for us. We work in Roath, Penylan, Cyncoed, Lisvane, Llanishen, Whitchurch, Rhiwbina, Radyr, Llandaff, Canton, Pontcanna, Grangetown, Splott, Rumney, Llanrumney and Cathays, and travel out to Barry, Newport and across South Wales. Call 07576 128903 or email Liamdunn2406@outlook.com, seven days a week from 7:00 to 21:30. Tell us the rough size of the driveway and the finish you have in mind, and we will tell you honestly whether sealing is worth it on your paving.