Cleaning block paving without re-sanding it afterwards is only doing half the job. Pressure washing, however careful, washes out a portion of the jointing sand between the blocks, and leaving those joints empty invites weeds, ants, and eventually loose, rocking blocks.
This guide covers choosing the right sand, getting the timing right after a clean, and the mistakes that lead to weeds pushing straight back through within weeks.
Why kiln-dried sand is the standard choice
Kiln-dried silica sand is dried to remove all moisture, which lets it flow freely into narrow paving joints and compact tightly, unlike builder's sand or damp sand which clumps and won't fill joints properly. It's also graded to a fine, consistent particle size that locks blocks together and resists being washed out as easily as coarser sand. Colour options are available too, useful for matching lighter or darker block paving so the joints don't stand out as an obvious grey line against the block colour.
Some kiln-dried sands are polymeric, meaning they contain a binding agent activated by water that sets the sand into a semi-rigid joint, offering better weed and ant resistance than plain sand, though at a higher cost and requiring more careful application per the manufacturer's instructions.
Getting the timing right
The paving needs to be completely dry before applying kiln-dried sand, since any residual moisture stops the sand flowing into the joints and causes it to clump on the surface instead. Depending on weather, this typically means waiting at least a full dry day, sometimes two, after pressure washing before re-sanding, which is exactly the step a lot of rushed DIY jobs skip.
Sweep the sand into the joints with a stiff broom working diagonally across the pattern, topping up and compacting with a plate compactor or hand tamper for larger areas, then brush off excess so no sand is left sitting on the block surface.
Common mistakes that lead to weeds
The most common mistake is not filling joints fully, leaving gaps just below the surface that look fine at first but give weed seeds an easy foothold within a season. Another is using the wrong sand type, since ordinary building sand doesn't compact or bind the way kiln-dried sand does and washes out again quickly in heavy rain.
Skipping re-sanding altogether after a clean is the biggest mistake of all: it might look fine for a few weeks, but empty joints are an open invitation for weeds, ants nesting under the blocks, and paving that gradually starts to shift and rock underfoot.
Costs and professional service
Kiln-dried sand costs relatively little to buy for DIY application, but professional paving cleans typically include re-sanding as standard, with the combined service costing around £4-£8 per square metre depending on area size and paving pattern. Having it done as part of the clean means no gap between washing out the old joints and refilling them, which is when weeds get their best chance to establish.
It's worth confirming re-sanding is included before booking a driveway clean rather than assuming, since some cheaper quotes cover the wash only and treat re-sanding as a chargeable extra. A slightly higher quote that includes it properly is usually better value than a cheap wash that needs a follow-up job within weeks.
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