Paving that has sunk in one corner of a patio

2 days ago
3 min read

Introduction

A patio laid last spring has developed a dip in one corner where water now sits after rain. The customer noticed it because a puddle appeared where there was not one before, and they would like to know why a new patio is already moving.

Settlement in one area is a sub-base issue in the overwhelming majority of cases. The slabs themselves rarely fail; what fails is what is underneath them, and that means the honest answer is usually about preparation rather than about materials. That is uncomfortable and it is usually true.

1. Paving that has sunk in one corner is telling you about the ground

The location is the diagnosis. One corner means one cause.

Made ground, soft spots and old features

A filled-in pond, a former border, a removed tree, a soakaway, a trench for a service. These compress under load and they are invisible once covered. Ask the neighbours if needed.

Insufficient depth or compaction

A sub-base laid too thin, not compacted in layers, or laid on soft ground without excavating properly. That is preparation and it is where most settlement originates. Be honest with yourself.

2. Look at the water as well as the ground

Water is often the mechanism. Ground plus water equals movement.

Check where the water goes

A downpipe discharging onto the corner, a missing gully, a fall that directs water into one area. Saturated sub-base moves under load. Follow the water in heavy rain.

Look at the falls across the whole patio

If water sits, the fall was inadequate somewhere. That is worth establishing before deciding on the repair, because relaying without correcting the fall repeats the problem. Check with a level.

3. Investigate before quoting anything

You cannot price what you have not seen. Take a slab up first.

Lift a slab and look

Bedding depth, sub-base thickness, whether it is wet, whether there is a void. Ten minutes with a slab up tells you everything. Photograph the section.

Ask what was there before

Customers often know about the old pond or the tree. That information changes the diagnosis and the conversation entirely. Ask before you speculate.

4. Be straight about responsibility

Landscaping disputes escalate quickly, so be clear early. Ambiguity makes it worse.

If preparation was inadequate, relay it properly

Excavate, replace and compact the sub-base correctly, and relay the area. It is expensive and it is the right answer. Do not patch the surface.

If the ground was unknowable, explain and be fair

Genuine made ground that nobody could have anticipated is a shared misfortune. Explaining it with the slab up and offering a reasonable contribution usually resolves it. Show them the void.

5. Prevent it at the quotation

Most of this is decided before any digging. Survey properly.

Excavate and inspect before pricing

Trial holes on anything you are unsure about. A quote given from the surface on unknown ground is a gamble you will sometimes lose. Allow for the worst.

Record what you found and what you allowed for

Depths, ground conditions, drainage arrangements. Written down, a later settlement conversation is factual rather than adversarial.

Conclusion

Localised settlement is a sub-base problem in almost every case, and the location tells you why: made ground, a filled pond, a removed tree, or a service trench, all invisible once covered — or simply a sub-base laid too thin or compacted in one lift.

Check the water too, because a downpipe discharging onto one corner will saturate and move the ground under load, and confirm the falls before deciding on a repair. Lift a slab and look rather than pricing from the surface, and ask the customer what used to be there. Relay properly where preparation was inadequate, be fair and explain where the ground was genuinely unknowable, and dig trial holes before quoting in future.