Why Your Patio Is Sinking (And How to Fix It Properly)

Why Your Patio Is Sinking

A sinking patio is one of the most common problems we're called out to fix. The good news is it's entirely preventable — and usually fixable without relaying the whole thing. Here's what's going on beneath the surface.

The Usual Cause: A Poor Sub-Base

Nine times out of ten, a sinking patio comes down to the sub-base. If the ground wasn't excavated deep enough, or the Type 1 MOT wasn't properly compacted in layers, the ground beneath the paving settles over time. The slabs follow it down.

Other common causes:

• No sub-base at all — slabs laid directly on soil or a thin bed of sand
• Inadequate compaction — the sub-base was laid in one thick layer instead of compacted in 50mm layers
• Soft spots in the ground — clay soil that wasn't identified and removed
• Water erosion — poor drainage washing material out from under the paving

Warning Signs

Catch it early and the fix is simpler. Look out for:

• Slabs that rock or move when you stand on them
• Puddles forming where the patio has dipped
• Gaps opening between slabs or against the house wall
• A visible slope where the patio should be level

How to Fix It Properly

The quick fix — lifting the affected slabs and adding more sand — will last you a season, maybe two. The proper fix takes longer but lasts decades.

1. Lift the affected area — remove the slabs in the sunken section
2. Excavate to a proper depth — at least 150mm below the finished level
3. Check the sub-base — remove any soft spots, made-up ground, or organic material
4. Lay and compact Type 1 MOT in layers — 50mm at a time, compacted with a whacker plate
5. Re-lay on a full mortar bed — not dot-and-dab, which lets water in and slabs move
6. Re-point the joints — with a proper jointing compound or sand-and-cement

Prevention Is Cheaper Than Cure

If you're having a new patio installed, ask your installer about the sub-base. A proper excavation and compaction process adds time to the job but it's the difference between a patio that lasts five years and one that lasts twenty-five.

Request a free online quote — we'll tell you honestly whether your patio needs a full relay or a targeted repair.

MSJ Landscaping — patio installers across South Manchester and Cheshire.