The only permanent way to stop weeds returning in block paving is to kill the roots, manually scrape out the joints, top them up with kiln-dried sand, and apply a high-quality polyurethane sealer to lock airborne weed spores out.
Weeds pushing up through your block paving make even the most expensive driveway look neglected. Pulling them up by hand is back-breaking work and if you leave the joints empty they will just grow back thicker next month. I have spent years restoring UK driveways and I can tell you that most quick fixes do more harm than good. In this guide, I will show you my exact method for eradicating block paving weeds and sealing the joints so they do not return. If you are looking to spruce up other areas, you can also check out our main hub for all things outside your home.
- Essential tools for block paving maintenance
- The salt myth: why you must never use salt on concrete paving
- Step 1: Manually remove the bulk (the block paving knife)
- Step 2: Pressure washing (the 45-degree rule)
- Step 3: Re-jointing with kiln-dried sand
- The Driveway Re-Sanding Calculator
- Step 4: Applying paving sealer to lock out spores
Essential tools for block paving maintenance
Before you start tackling the weeds, you need to gather the right equipment to do the job properly.
Mat’s tool bag:
- Block paving weeding knife
- Long-handled wire brush
- Pressure washer (read our Karcher K3 review if you need a reliable option)
- Bags of kiln-dried sand
- Polyurethane block paving sealer
- Low-pressure sprayer or a sealing roller
- PPE: Heavy-duty gloves and protective eyewear
The salt myth: why you must never use salt on concrete paving
I frequently see internet articles recommending a homemade mixture of salt and vinegar to kill driveway weeds. You must avoid this at all costs. While salt will certainly dehydrate and kill a weed, it is incredibly damaging to concrete block paving.
Salt draws moisture out of the concrete and causes a chemical reaction called efflorescence, leaving stubborn white stains across your driveway. Worse still, salt accelerates freeze-thaw damage during the British winter. The saline mixture pools in the micro-cracks of the concrete, freezes, expands, and blows the face off your expensive paving blocks. It is a hack that could cost you thousands of pounds in repairs.
Step 1: Manually remove the bulk (the block paving knife)
Start by physically scraping the joints clean using a dedicated weeding knife and a wire brush to remove the thickest root systems.
Take your block paving knife and drag it through the joints to hook out the thick moss and established weed roots. A long-handled wire paving brush is brilliant for scrubbing out the remaining green residue. If the weeds are heavily overgrown, you may need to apply a chemical treatment first. You can read our guide on the best weed killers for block paving to find a suitable product.
For those wanting to avoid chemicals completely, the Royal Horticultural Society provides excellent advice on non-chemical weed control for hard surfaces.
[Visual Cue: Insert a high-quality photo of a long-handled wire block paving brush clearing out a thick mossy joint.]
Step 2: Pressure washing (the 45-degree rule)
Wash the driveway to remove remaining debris but always hold the pressure washer lance at a 45-degree angle to protect the bedding sand.
A pressure washer will blast out the tiny weeds and dirt that your knife missed. However, you must be incredibly careful with your technique. Do not point the nozzle straight down into the joints. If you do this, you will blast the essential bedding sand right out from under the paving blocks, causing your driveway to sink and become dangerously uneven.
Always hold the lance at a 45-degree angle to the paving. This cleans the chamfered edges of the blocks thoroughly without excavating the foundation below.
Step 3: Re-jointing with kiln-dried sand
Once the paving is bone dry, you must refill the joints completely using only fine kiln-dried sand.
You must wait at least 24 hours after pressure washing before moving to this step. The paving must be absolutely dry. Never use standard building sand or sharp sand for this job. You need kiln-dried sand, which is incredibly fine and contains zero moisture, allowing it to flow freely into the tightest gaps.
Tip a bag onto the paving and use a soft-bristled broom to sweep it into the joints. Always sweep diagonally across the joints. If you sweep parallel to the gaps, the bristles will just dig in and pull the sand straight back out. Ensure every joint is filled flush to the bottom of the block’s chamfer.
The Driveway Re-Sanding Calculator
The Driveway Re-Sanding Calculator
Enter the dimensions of your block paving below to find out exactly how much kiln-dried sand and sealer you need for the job.
Total Area: 0 m²
Kiln-Dried Sand Required: 0 x 25kg bags
Paving Sealer Required (2 Coats): 0 Litres
Step 4: Applying paving sealer to lock out spores
Sealing the paving solidifies the sand and creates a waterproof barrier that stops airborne weed spores from taking root.
Applying a sealer is the ultimate preventative measure. Before applying a solvent-based sealer, you need a very specific UK weather window. You need three consecutive dry days with temperatures consistently above 10°C, and you must wait until the morning dew has completely evaporated. Applying sealer to damp blocks will trap moisture and turn the sealer a milky white colour.
Apply your chosen patio sealer using a low-pressure sprayer or a roller. You generally need two coats. The first coat soaks into the kiln-dried sand to set it rock hard. The second coat provides the surface protection that stops weed spores and oil stains from penetrating the blocks. Allow the driveway to cure for at least 3 hours before walking on it and keep vehicles off it for a full 24 hours.
