The short answer
Cleaning existing block paving properly follows four steps: pre-treat the surface with a moss, weed and algae killer and clear loose debris; pressure-wash the blocks evenly, keeping the lance moving and at a consistent angle so you do not gouge the surface or blast out more sand than necessary; let it dry; then re-sand the joints with kiln-dried sand, brushed in until the joints are full, which locks the blocks together and slows weed regrowth. An optional final step is sealing once the paving is fully dry. The two most common mistakes are holding the lance too close or static, which scars the blocks, and skipping the re-sanding, which leaves the paving loose and quick to grow weeds again.
Block paving is the surface most often damaged by careless washing, because the joints between blocks are part of how it stays stable. Here is the method a specialist follows — and what to avoid if you tackle it yourself.
The four steps
- 1. Pre-treatmoss/weed killer, clear debris
- 2. Pressure-washeven passes, lance kept moving
- 3. Drylet joints dry before sanding
- 4. Re-sandkiln-dried sand brushed in
- Optionalseal once fully dry
The step-by-step method
- Pre-treat: apply a biocide or moss-and-weed treatment a few days before, and sweep off leaves, weeds and loose grit so the wash reaches the surface.
- Pressure-wash: work in steady, overlapping passes with the lance kept moving and at a consistent height and angle. This cleans evenly without scarring the blocks or stripping out more jointing sand than necessary.
- Let it dry: the joints must be dry before sanding, or the new sand will clump rather than settle.
- Re-sand: brush kiln-dried sand across the surface and into the joints, topping up until they are full. This is what locks the blocks together and resists weed regrowth.
Mistakes that damage block paving
The damage people see after a DIY wash almost always comes from a few avoidable errors. Holding the lance too close or letting it dwell in one spot gouges the block faces and leaves stripey 'tiger marks'. Using too high a pressure setting can fracture older or softer blocks. And skipping the re-sanding leaves the joints empty, so the blocks rock, weeds return fast and the surface deteriorates. Re-sanding with kiln-dried sand is not an optional extra on block paving — it is part of doing the job properly.
Want block paving cleaned properly?
We'll match you with a vetted driveway and patio cleaning specialist who pre-treats, washes evenly and re-sands the joints with kiln-dried sand as standard.
Frequently asked questions
How do you clean block paving without damaging it?
Pre-treat for moss and weeds, then pressure-wash in steady overlapping passes with the lance kept moving at a consistent angle, and finish by re-sanding the joints with kiln-dried sand. Holding the lance too close or static is what scars the blocks.
Do you need to re-sand block paving after cleaning?
Yes. Pressure-washing lifts the jointing sand out from between the blocks, so kiln-dried sand should be brushed back into the joints once the paving is dry. This locks the blocks together and slows weed regrowth.
Can I clean block paving myself?
A small, lightly soiled area can be done with care and the right kiln-dried sand to finish. Large, heavily weeded or rocking-block drives are usually better left to a specialist with commercial equipment, to avoid scarring the blocks.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific surface. They are guidance, not a quotation.