Why is the base so important for block paving?
Block paving is a flexible surface. The blocks spread a load over a wider area, but they rely entirely on the layers below to carry it. If the base is strong, uniform and drained, the surface stays level for a long time. If it is weak in places, those places show first as dips, ruts or rocking blocks.
The base is also the part nobody sees once the job is finished, which is why faults there are common. A driveway can look excellent on the day it is handed over, with straight lines and clean joints, while the sub-base underneath is already too thin for the cars that will use it. The surface only tells the truth later.
What happens when the sub-base is too thin?
A thin sub-base cannot spread wheel loads far enough before they reach the natural ground. The ground then deforms under each pass, and over time the surface follows it down. On a driveway the result is usually twin ruts along the tyre lines; on a path used by a delivery vehicle, it may be a single dished strip.
The right thickness depends on the ground, the traffic and the materials, and it is a design decision. Our network does not draft projects; for traffic loads in general, our driveway site has a guide to bases for traffic loads. In a repair, the correction is to excavate the weak area and rebuild it with suitable granular material, compacted properly, so it matches the use the surface actually gets.
Why does compaction in layers matter?
Granular material only becomes strong when it is compacted, and compaction equipment only reaches so far down. If a deep layer is tipped in one go and compacted from the top, the upper part may be firm while the lower part stays loose. That loose layer then settles under traffic and rain.
From the surface, poor compaction tends to show as broad, uneven settlement that appears within the first year or two, often described by owners as the new drive falling apart. In a repair we remove the loose material and replace it in thinner lifts, compacting each one before adding the next. It is slower, but it is the only way to get a uniform result.
What is wrong with leaving soil or roots in the formation?
The formation is the ground the sub-base sits on. Topsoil, vegetation and old roots should be removed before the base goes down, because they compress and decay. If they are left, the base above slowly loses support, and the surface develops soft spots that often feel springy before they visibly sink.
When we open paving with this fault, we usually find a dark, organic layer directly under the granular material. The fix is to dig it out, bring the formation down to firm natural ground and rebuild the base. In gardens, a geotextile is sometimes laid to separate the base from the soil and stop fines migrating between the two.
Can the bedding layer itself cause sinking?
Yes. The bedding layer is meant to be thin and even. It gives the blocks a level seat; it is not there to make up for an uneven base. When an installer uses extra bedding to fill hollows in the sub-base, the thick areas compress more under load than the thin ones, and the surface ripples.
Unsuitable bedding material causes similar trouble. Very fine sand can wash out through the joints when water flows over it, and material with a lot of dust can hold water and lose strength. In a repair, the old bedding is always removed and replaced, because it is impossible to tell how much of it has migrated or been contaminated.
Why do missing or weak edges lead to sinking?
Block paving only works if the blocks are held tightly together. That is the job of the edge restraint: a kerb, an edging course or a solid wall that stops the outer rows from moving. Concrete kerbs are covered by UNE-EN 1340 with the Spanish complement UNE 127340; natural stone kerbs by UNE-EN 1343.
When the edge is missing, set too low or not haunched firmly in concrete, the outer blocks creep outwards under traffic. Joints open, the interlock is lost and the blocks near the edge drop. Repairs include resetting or replacing the edging; new edging as a stand-alone job is covered on the kerbs and edge restraint page.
How does trapped water undermine an otherwise good base?
Even a well-compacted base can fail if water gets in and cannot get out. Water arrives through joints, from downpipes or from higher ground, and in a build-up with no outlet it sits in the base and softens it. Under traffic, saturated material loses strength quickly.
The correction is usually a combination of measures: setting the surface falls so water runs off, adding or clearing a channel drain or gully, and redirecting downpipes away from the paving. Where water still collects, our drainage and standing water service looks at where the surface water can realistically go.
Is a concrete base better than a granular sub-base?
Not automatically. A concrete slab gives a rigid support, which can help under heavy loads, but it needs its own falls and drainage, because water reaching the bedding has nowhere to go. A granular sub-base is flexible and free-draining if built properly. Each has its place, and our pillar site explains the concrete base option.
For repairs, we generally rebuild with the same type of support that the surrounding paving uses, so the repaired area behaves like the rest. Mixing a rigid patch into a flexible surface can create a hard spot with a step at its edges once the surrounding paving moves.
Which base faults can be fixed locally and which cannot?
Faults with a clear boundary can usually be corrected locally: a soft spot over buried organic material, a short length of failed edging, a poorly compacted ring around a chamber. Faults that run through the whole build-up, such as a sub-base that is uniformly too thin for the traffic, are a different matter and usually call for a wider relay.
The repair or replace guide sets out how we make that call. What matters is that the decision is based on what the base looks like when it is opened in more than one place, not only on how bad the worst dip appears from the surface.
How can you spot base faults before you hire someone?
You cannot see the base, but you can ask the right questions and look for the right signs. A contractor should be able to explain what they will put under the blocks and how they will compact it. When you look at existing paving, these clues point to base faults:
- settlement within the first year or two after laying
- ruts that follow wheel lines
- blocks creeping outwards at an edge
- soft or springy areas when walked on
- joints that keep emptying after being refilled
If you recognise these signs, our subsidence diagnosis or a lift and relay repair are the natural next steps. Send us a photo and the approximate m² – free, no-obligation quote. Photos of the edges and of any ruts are especially useful at the first stage.
Frequently asked questions
What are the signs of poor sub-base installation?
Early settlement within a year or two, ruts along the tyre lines, soft or springy patches, blocks spreading at the edges and joints that keep opening are the usual signs. Together they suggest the sub-base was too thin, poorly compacted or laid on unsuitable ground.
Can a defective sub-base be fixed without replacing the blocks?
Yes. The blocks are lifted and set aside, the defective sub-base is dug out and rebuilt, new bedding is laid, and the same blocks go back in their pattern. Only damaged blocks need replacing.
How deep should a garden path sub-base be?
It depends on the ground, the use and the materials, and it is a design decision rather than a fixed number. A path used only on foot needs less than a route a vehicle might cross. We assess the existing build-up and the use when we open the paving.
Is a concrete base better than a sub-base beneath block paving?
Neither is better in every case. A concrete base is rigid and suits some heavy-load situations, but it needs its own drainage. A properly built granular sub-base is flexible and free-draining. In repairs we normally match the support used under the surrounding paving.
Why does thick bedding make paving uneven?
Bedding compresses under load. Where it is thick, it compresses more than where it is thin, so the surface ripples. Bedding is meant to be a thin, even seat, not a filler for hollows in the base. Uneven bases should be corrected before bedding is laid.
What does edge restraint have to do with sinking?
Block paving relies on the blocks being held tight against each other. Without a firm edge, outer rows creep outwards, joints open, the interlock is lost and blocks near the edge drop. Fixing the edge is usually part of repairing sinking at the sides.
Why did my new driveway start sinking after nine months?
Early sinking usually points to a construction fault rather than wear: insufficient or poorly compacted sub-base, soil left in the formation, thick bedding or missing edges. Opening the paving in the worst area normally shows which one, and the repair corrects that layer.
Can water ruin a properly built base?
A well-built base drains, but if water keeps arriving and cannot escape, it saturates the material and weakens it. That is why falls, channel drains and downpipe outlets matter as much as compaction when you want paving to stay level.
Do you draw up designs for new bases?
No. We are a contractor that carries out the works; we do not draft projects or geotechnical studies. For repairs we rebuild the base to suit the existing use and surroundings, and where a project is needed it has to come from a qualified professional.
Is a geotextile always needed under the sub-base?
Not always. A geotextile helps separate the base from soft or clay-rich soil and stops fine particles mixing into the granular layer. Whether it is useful depends on the ground found when the area is opened, so it is decided case by case.