In short
Block paving sinks because the sub base under it was too thin, was not compacted properly, or has been washed out by water. The blocks themselves rarely fail. A dip by the house is usually a leaking downpipe or drain; ruts in the wheel tracks mean the whole base is too weak for the load.
This is a job for our Block Paving service.
Where the dip is tells us the cause
Block paving is a flexible surface. It sits on a bed of sand over compacted stone, and it only stays flat if that stone stays put. When it sinks, the position of the dip points to the reason.
- A hollow next to a downpipe, gully or manhole. Water has been running under the paving and washing the sand and fines out of the base. Often the drain connection has failed.
- Two ruts where the car wheels sit. The base is too thin or was never compacted, so it has consolidated under the repeated load of a vehicle.
- Blocks spreading and gaps opening at the edge. The edge restraint has failed or was never there, so the blocks have crept sideways and the surface has dropped.
- A general wave across the whole drive. The ground itself is moving, which on the clay around Horsham, Cranleigh and Uckfield usually means a wet-and-dry cycle in soil that was not dug out far enough.
What a block paved drive should be sitting on
Marshalls' own laying guide calls for a minimum 100mm of MOT Type 1 sub base, compacted in two courses with six or seven passes of a plate compactor, then 50mm of sharp sand, concrete edge restraints and a fall of about 1cm in every 60cm so water runs off. We build driveways to at least that, and on soft ground or where vans and horseboxes use the drive we go deeper. Most of the sunken drives we open up have less than half that depth of stone, or stone that was tipped and levelled but never compacted.
How we repair sunken block paving
The good news is that block paving is the one surface you can take up and put back. If the blocks are sound, repair is usually the right call.
- Lift the blocks over the sunken area and a margin around it, and set them aside in order.
- Find the cause. If it is water, fix the drain or downpipe first, or the dip will come back.
- Dig out the soft material, bring the base back up with Type 1 in layers and compact each one.
- Re-screed the sand bed, relay the same blocks, compact and re-sand the joints.
If the ruts run the length of the drive, or the edges have spread everywhere, patching one area moves the problem along. In that case we recommend lifting the lot, rebuilding the base and relaying, reusing the blocks where they are in good condition.
When it is not the base
A few dips are caused by tree roots lifting one side, or by a service trench across the drive that was backfilled with loose soil. We check both before we quote, because the fix is different and so is the price.