It's easy to assume a tired-looking block-paved drive just needs a good clean, and often that's exactly right — moss, staining and a colour that's faded under grime all respond to cleaning and re-sanding without touching the structure underneath. But some driveways have a genuine sub-base problem hiding under the same dirty surface, and no amount of cleaning fixes that.
The distinction matters because relaying is a groundwork job, not a cleaning one, and it's a waste of money to clean and seal a surface that's going to keep moving underneath the new finish.
Signs that point to a cleaning-only fix
- Uniform surface staining, moss or algae across the whole area rather than concentrated in one section.
- Blocks that are individually sound and don't rock underfoot when walked on.
- Joints that have lost sand generally through cleaning and weathering, rather than through movement.
- No visible dips, ridges or pooling water that suggest the ground beneath has shifted.
Signs the problem sits below the surface
- A section of blocks that rocks, sinks or rises as a group rather than as individual loose blocks.
- Repeated sinking in the same spot after previous re-sanding or minor repair.
- Standing water pooling in a dip that wasn't there when the drive was new.
- Rippling or wave-like unevenness across a run of blocks, suggesting the bedding layer has shifted.
Why cleaning can't fix a sub-base issue
Block paving relies on a compacted sub-base and bedding layer to hold its shape; the blocks themselves are essentially loose units held in place by that foundation and the sand-filled joints. If the foundation has settled, washed out, or was never compacted properly, no amount of surface cleaning or re-sanding addresses the actual cause.
Cleaning over a sub-base problem can even make it more visible, since a bright, freshly cleaned surface shows dips and unevenness more clearly than a dirty one did.
When a partial relay is enough
A localised dip or a small area of sunken blocks caused by isolated settlement — over a utility trench, for instance — often only needs that specific section lifted, the base corrected and the blocks re-laid, rather than the whole drive being taken up. Being honest about the scale of the problem before recommending a fix matters here, since a full relay is a significant undertaking compared with a targeted repair.