Patios sink or crack when the base underneath fails — through poor original installation, ground movement, or water washing out the material the slabs are bedded on — rather than through a problem with the slabs themselves.
A patio is only as stable as what's underneath it. If the sub-base wasn't properly compacted when the patio was laid, or if water has found a way to erode the bedding material over the years, individual slabs lose their support and start to rock, sink, or crack under normal weight. Tree roots growing underneath a patio can cause similar movement, lifting some slabs while others stay in place.
It's worth being clear on the difference between a patio that's damaged and one that's just dirty. Green algae, moss and general grime don't affect the structure of a patio at all — that's a cleaning job, and pressure washing sorts it. Cracked, sunken, loose or rocking slabs are a different problem entirely, caused by what's happening beneath the surface, and cleaning won't fix any of it.
Repairing a patio properly means addressing the base, not just replacing the visible slab — otherwise the same section is likely to sink again within a season or two. This is one of the most common repair enquiries we get from homeowners across Preston and Lancashire, especially on patios more than a few years old.
GreenFix provides patio repairs across Preston and Lancashire. From £95 (guide price only, confirmed after assessment).
