Why block paving sinks

By Taylor Teasdale, Owner · 28 October 2026

Blocks do not sink. What is underneath them moves, and the blocks follow. That one sentence explains almost every driveway problem anyone ever calls us about.

The useful part is that the shape of the problem tells you what went wrong, and what it will take to fix it.

Two parallel ruts where the car goes

Known as tramlining, and the most common fault of the lot. The sub-base is too shallow for the load, or it was tipped in and rolled in one go rather than built up and compacted in layers.

A driveway needs its sub-base compacted in layers — usually 75 to 100mm at a time — because a whirlacker or roller only consolidates so far down. Dump 200mm in one go and the top is solid while the bottom is still loose. It looks perfect for a year, then the wheels find the weakness.

The fix: this is a base problem across the whole driveway, so relaying the blocks alone will not hold. It needs excavating and rebuilding, at least across the trafficked area.

One sunken patch

A single dip, often rectangular and often near the boundary or across the middle, almost always means a service trench. Water, gas, electricity or drainage was dug in at some point and the backfill was never compacted properly. It settles for years afterwards.

Also common: a soft spot where a tree was taken out, an old pond or soakaway, or where made-up ground was never dug down to something solid.

The fix: local. Lift the blocks over the affected area, dig out the soft material, backfill and compact properly, relay the same blocks. This is a genuinely good repair, not a patch.

The edges are creeping outwards

Block paving works by interlock — the blocks lock against each other and spread load sideways. That only works if the perimeter cannot move. Edge restraints should be bedded and haunched in concrete.

Where the restraint was laid on sand, or never properly haunched, the edge pushes out under load and the whole field of blocks slowly loosens behind it. You will usually see widening joints along the edge first.

The fix: rebuild the edge restraint properly and re-tighten the field. Catch it early and it is a straightforward job; leave it and the loosening spreads inwards.

Blocks that rock when you step on them

Usually the joints have lost their sand. Jointing sand gets washed out by rain, blown out, or — most often — blasted out by a pressure washer held too close. Without sand in the joints there is no interlock, and individual blocks move independently.

The fix: the cheapest on this page. Re-sand the joints with kiln-dried sand and vibrate it in, or use a polymeric jointing compound that sets firm and does not wash out. If the blocks are rocking but the surface is still flat, you have caught it in time.

Water standing after rain

Either the falls were never set correctly, or the surface has settled enough to create a low point. Water should run off to a drain, a channel or a permeable area; anywhere it ponds, it will eventually cause a problem, because water in the base is what frost acts on.

The fix: depends on whether the levels are wrong or the base has moved. A test hole answers it.

How to tell which one you have

Dig a hole. Genuinely — lift a few blocks at the worst point and look at what is underneath. You are looking for how deep the sub-base is, whether it is clean angular stone or a mix of soil and rubble, and whether it is damp and soft or dry and tight.

That is exactly what we do at a site visit before quoting a repair, because the alternative is guessing. A driveway with 200mm of properly compacted sub-base and one settled trench is a half-day repair. A driveway with 80mm of crusher run over topsoil is a relay, and no amount of work on the surface will change that. You deserve to be told which one you have before you spend anything.