How to Clean Block Paving Without Washing Out the Joints

Block paving looks tired quickly when it is left alone. Tyre marks, moss, algae, weeds and the odd oil drip build up, and a grey or green film can make a driveway look years older than it is. The good news is that most of this comes off with the right method. The bad news is that the most common way people clean it, blasting it with a pressure washer, is also the quickest way to damage it.

This guide explains how to clean block paving properly, how to use a pressure washer without stripping out the joints, and how to re-sand afterwards so your driveway stays firm and level.

Why the joints matter

The thin lines of sand between the blocks are not just filler. When the paving is laid, sand is brushed into the joints and compacted, which locks the blocks together so they spread the weight of a car across the whole surface. That is what stops individual blocks moving.

When the sand is washed out, blocks start to rock and shift, edges can chip, and weeds find an easy place to grow. Over time, loose blocks can sink or spread, especially where cars turn. So the goal when cleaning is simple: remove the dirt but keep the sand, or put it back straight afterwards.

What you need

• A stiff yard brush and a hand brush for corners
• A bucket of warm water and a mild detergent, or a cleaner made for block paving
• A weeding knife or patio knife for the joints
• A pressure washer (optional), ideally with a rotary patio cleaner attachment
• Kiln-dried sand to refill the joints
• Gloves and eye protection if you are using cleaning products

Before you start, check the forecast. You need a dry spell after cleaning so the paving can dry out before you re-sand it.

How to clean block paving step by step

1. Clear and sweep the surface

Move cars, bins and pots off the driveway, then sweep it thoroughly with a stiff brush. Getting loose dirt, leaves and grit off first stops you grinding it into the surface or pushing it into the joints when you wash.

2. Remove weeds and moss from the joints

Run a weeding knife along the joints to lift out weeds and moss, then sweep up what comes loose. Try to take out the roots rather than just the tops, because anything left behind grows back quickly.

3. Wash the surface

For light dirt, warm water with a little detergent and a stiff brush is often enough. Work in small sections and scrub in overlapping circles. If the paving is heavily stained or green, a cleaner made for block paving or a pressure washer will save time; see the next section for how to use one without damaging the joints.

4. Rinse

Rinse each section with clean water so no detergent is left on the surface, as leftover residue can attract dirt. Avoid rinsing cleaning products into flower beds or drains, especially stronger chemical cleaners.

5. Let it dry completely

Leave the paving to dry, ideally for a full dry day. The joints need to be dry before you re-sand, otherwise the sand clumps at the surface and does not fall into the gaps.

6. Re-sand the joints

Brush kiln-dried sand back into the joints. This is the step most people skip, and it is the one that keeps your block paving firm. It is covered in more detail below.

Using a pressure washer safely

A pressure washer cleans block paving quickly, but used the wrong way it strips sand out of the joints and can mark or scar the face of the blocks. If you use one:

• Use low to medium pressure. Start on the lowest setting that cleans and only increase it if you need to.
• Hold the lance at a shallow angle, spraying across the blocks diagonally rather than straight down into the joints.
• Keep the nozzle moving in a steady sweeping motion. Holding it on one spot is how marks and lines appear.
• Use a rotary patio cleaner if you have one. Its spinning head and hood spread the force more evenly and reduce how much sand is blown out.
• Test a small hidden area first, especially on older or softer blocks.

Even with care, a pressure washer will lift some jointing sand, so plan to re-sand afterwards. Newly laid block paving should not be pressure washed for at least the first few months while the joints settle.

Re-sanding the joints after cleaning

Kiln-dried sand is the right sand for this job. It is very fine and completely dry, so it flows down into narrow joints and packs them fully. Building sand is too coarse and damp and will not fill the gaps properly.

1. Wait until the paving and joints are completely dry.
2. Pour small piles of kiln-dried sand across the surface.
3. Brush it diagonally across the joints in different directions until they are full to the top.
4. Sweep off the excess so the surface is clean.
5. Check again after a week or two, as the sand settles, and top up any joints that have dropped.

As a rough guide, buy a little more sand than you think you need. Running out halfway through is more annoying than having a spare bag for topping up later.

Removing oil, rust and other stains

Fresh oil. Act quickly. Soak up as much as possible with an absorbent material such as sand, sawdust or cat litter, leave it for a while, then sweep it up. Do not spread the oil around with water first.

Older oil stains. Use a degreaser or oil stain remover made for block paving, following the instructions carefully. Deep, old stains may fade rather than disappear completely.

Rust marks. These usually come from metal furniture, iron gutters or garden tools. Use a rust remover suitable for paving, test it on a hidden block first, and remove the cause so the stain does not come back.

White bloom on new paving. A chalky white haze on new concrete blocks is usually efflorescence, a natural salt deposit from the cement. It is not a fault and normally fades with rain and use over the first months, so it is usually best left alone.

Whatever you use, always try it on a small, hidden area first. Some cleaners can lighten or discolour blocks, and clay pavers in particular should not be treated with chemical cleaners. The block paving cleaning guide from Marshalls is a useful reference for product-specific advice.

Weeds, moss and sealing

Weeds and moss grow where joints are empty or where dirt has built up in them, so the best prevention is full joints and regular sweeping. Brushing the surface every week or two disturbs new growth before it can take hold, and shady, damp areas will need more attention than sunny ones.

Some homeowners seal their block paving after a deep clean. A sealer can help hold the jointing sand in place and make stains and weeds less likely, but it is optional and needs reapplying over time. If you do seal, the paving must be clean, fully dry and properly re-sanded first.

How often to clean block paving

A quick sweep every week or two does most of the work. A deeper clean once or twice a year is enough for most driveways, typically in spring to clear winter grime and moss, and after autumn to remove leaves before they stain. Shaded driveways under trees may need it more often.

Each time, check the joints. If you can see gaps forming, top them up with kiln-dried sand before weeds move in.

When cleaning is not enough

Cleaning will not fix blocks that have sunk, rocked loose or spread at the edges. These usually point to a problem underneath, such as a weak sub-base, failed edging or water getting under the surface. Pressure washing a driveway in this state can make things worse.

Sunken areas can usually be lifted, re-bedded and relaid using the original blocks, so a full replacement is often not needed. If your driveway has dips, puddles or loose blocks, our driveway repairs team can assess it. And if you would rather not clean and re-sand it yourself, our block paving contractors also clean, repoint and maintain block paving across North London.