What the sub-base actually does
The sub-base spreads the point load of a vehicle wheel across a much wider area of ground. Without enough depth of well-compacted stone, that load concentrates and the sub-grade below deforms — which is what rutting, dipping and cracking really are.
It also keeps water moving. A well-graded, properly compacted stone layer stays stable when wet; soil and unsuitable fill do not.
Depth is dictated by the ground and the use
There is no single correct depth. Firm, well-draining sub-grade under a light car needs less than soft clay under a van, and Newcastle has plenty of both.
The right approach is to dig, look at what is actually there, and specify accordingly. Any quote that names a depth before the ground has been seen is guessing.
Membranes and layers
Where the sub-grade is soft, a geotextile membrane between soil and stone stops the two mixing. Without it, the expensive stone slowly disappears into the clay and the base thins over the years.
Compaction has to be done in layers. Stone tipped to full depth and rolled once looks compacted at the surface and is loose underneath — a failure waiting for its second winter.
- Geotextile membrane on soft or clay sub-grades
- Compaction in layers rather than one deep lift
- Well-graded crushed stone, not builders' rubble
- Edge restraints installed onto the compacted base
How to spot a thin quote
Look for three things: excavation depth, sub-base material and depth, and edge restraint detail. If they are absent, the quote is describing a surface, not a driveway.
It is also fair to ask what happens if the ground turns out worse than expected. We would rather agree that in advance than have an awkward conversation on day two.
Frequently asked questions
Can you lay a new surface over my old driveway?+
Sometimes, if it is structurally sound and drains properly. Overlaying a failing base just hides the problem for a season.
What if you find something unexpected when digging?+
We stop, show you, and agree the approach before continuing. No work goes ahead unagreed.
Is builders' rubble acceptable as sub-base?+
No. Uncontrolled fill does not compact predictably and is a common cause of later settlement.
Does a patio need the same base?+
Similar principles, generally less depth, since there is no vehicle loading — but falls and bedding matter more.
Want a quote with the base spec in writing?
That is how we quote as standard — excavation depth, sub-base, edging and drainage all listed.