Why do block paving driveways sink, and can they be fixed?
By Terry O'Reilly, owner, 17 years on the tools. Updated . 4 min read.
Block paving sinks because the base under it fails: too little compacted stone, stone that was never properly compacted, water getting under the drive on Milton Keynes clay, or a utility trench that was backfilled loose. The good news is that block paving can be lifted, the base rebuilt, and the same blocks relaid with no visible join. A patch is a day's work and a full relay is well under the price of a new drive.
What makes a block paving driveway sink?
Blocks do not sink. The ground under them does. Every sunken drive I have lifted in Milton Keynes has come down to one of these four things, and often two of them together.
- No sub-base, or not enough of it. A drive needs 200mm to 250mm of compacted stone under the sand. A lot of drives were laid on 50mm, or on the old soil with a bit of sand over it. The first winter the ground softens, the car pushes the blocks down, and the dip appears where the wheels sit.
- Poor compaction. Stone tipped in and levelled is not the same as stone compacted in layers with a plate. Loose stone settles for years. The drive looks fine on the day and starts to roll like a wave by the second summer.
- Water. Milton Keynes sits on clay, and clay swells when wet and shrinks when dry. If rain runs under the drive because there is no slope to carry it away, no edge or no drainage, the ground moves with every season and the blocks move with it. Soft spots near a downpipe or a leaking gully are the classic sign.
- Utility trenches. Gas, water and electric all run under the front. When one of them is dug up and the trench is backfilled with loose soil, the strip over it sinks. If the paving firm did not compact the trench before laying, the same thing happens on a brand-new drive.
Spreading edges cause it too. If the edging was not set in concrete and backed with concrete, the outer blocks push out under the car, the sand bed spreads, and the middle drops.
How can I tell why mine has sunk?
Stand at the road and look along the drive at ground level. Two straight dips where the wheels go and a firm middle means the base is thin or badly compacted. A dip in one spot, usually near a drain or a downpipe, means water is getting under and washing the sand and fines away. A straight strip across the drive, often from the pavement to the house, is a utility trench. Blocks tipping up at the edges and a gap opening against the lawn is the edging giving way.
Pull one loose block up if you can. If you see sand and then soil, there is no base. If you see sand and then stone, the base is there but it may be thin or loose. A photo of the dip and the hole on WhatsApp usually tells me which it is before I visit.
Would you rather just ask Terry?
A photo and a question on WhatsApp gets a straight answer, usually the same day.
Can a sunken block paving drive be fixed without replacing it?
Often, yes, and that is one of the reasons I recommend block paving in the first place. The blocks come up, the base is dug out and put back properly, the sand bed is relaid and the same blocks go back down. Because they are the original blocks, weathered to the same colour, you do not see the join. A sunken strip over a trench or a dip by a drain is a day's work. That is the job on our driveway repairs and relaying page.
A full relay of a two-car drive, lifting everything and rebuilding the base from scratch, is a bigger job. It is still less than a new drive because there are no blocks to buy and no old surface to skip, typically less than a new one. Whether that is worth it depends on the blocks. If they are sound and you like them, relay. If they are crumbling, faded or a pattern you never liked, it is usually better to put the money into a new drive; the block paving cost guide explains what moves the price.
What does a repair cost compared with a new drive?
| Job | What it involves | Relative to a new drive | Time |
|---|---|---|---|
| Patch relay | One dip, one trench or one edge lifted, base rebuilt, same blocks back | A small fraction | Half a day to a day |
| Full relay | All blocks up, new 200mm to 250mm stone base, new edging where needed, same blocks back | Less than new | 2 to 3 days |
| New drive | Everything out, new base, new blocks | Full price, see the cost guide | 2 to 3 days |
Swipe the table sideways to see all of it.
How do I stop a new drive sinking?
Insist on these in writing before anyone starts, from us or anyone else.
- 200mm to 250mm of compacted stone, laid in layers and compacted with a plate, not tipped and raked.
- Edging set on concrete and backed with concrete.
- A fall on the surface and somewhere for the water to go: a channel drain, a soakaway or the lawn.
- Any utility trench dug out and compacted before the base goes on.
- A guarantee in writing that covers sinking. Ours is ten years.
The whole day-by-day process is in what happens when we lay a block paving drive. We repair and relay across Milton Keynes, from the 1930s semis in Bletchley to the newer estates around Shenley, and out to Leighton Buzzard. Before and after photos are on our work page.
