What's Under a Resin Driveway in Lincoln: Limestone, Clay and Made Ground

Dig 300mm down at the top of Steep Hill and you hit rock. Dig the same hole a mile away in the Witham valley and you are into soft grey clay that shines when you cut it. Both addresses have a Lincoln postcode, both want a driveway, and the specification that suits one is genuinely wrong for the other. The Lincoln Cliff rises around 50 metres above the ground to the west of it, and that ridge is not just scenery, it is a geological boundary running straight through the middle of the city. Roughly a third of the driveways we look at sit close enough to it that the ground changes between the gate and the garage. This is a guide to what actually goes under the resin, arranged by what you are building on rather than by layer, because in Lincoln that is the question that decides everything else.

Lincoln Is Two Towns, Geologically

The escarpment locals call the Cliff, and geologists call Lincoln Edge, is formed by the Lincolnshire Limestone Formation, a hard Jurassic limestone that also happens to be the stone the Cathedral is built from. It caps the high ground on the east side. To the west and below, the land falls onto Charmouth Mudstone, a Lower Jurassic clay laid down somewhere between 199 and 183 million years ago. The valley floor on top of that carries Belton sand and gravel plus more recent alluvium and river terrace deposits along the Witham itself.

Translated into driveway terms: uphill you are usually building on something that already carries load. Downhill you are usually building on something that does not, and that changes shape with the seasons. You can look up your own address on the British Geological Survey’s geology viewer in about a minute, and it is worth doing before you read anyone’s quote.

None of this makes a resin bound driveway a bad idea in either half of the city. It just means the same price per square metre should not apply to both.

Uphill: Building on Lincolnshire Limestone

Around the Bailgate, up Nettleham Road, out towards Burton and the northern edge of the city, the limestone is often not far down. Where it is, the ground is about as good as domestic groundwork gets. It carries weight, it does not shrink and swell with the weather, and once you have dug through the topsoil you are onto something stable.

The catch is drainage, and it is the opposite of the problem people expect. Limestone can be fissured, so water sometimes disappears very readily, and sometimes hits a tighter band and sits. Neither is a disaster for a permeable drive, but they call for different answers, and the only way to find out which you have is to dig a hole and watch it.

The other uphill catch is depth. Where rock sits at 200mm you cannot simply excavate to your preferred formation level, and you should not be breaking it out either. The sensible response is to build up rather than dig down, taking the finished level higher and dealing with the consequences at the thresholds and the boundary. That is a design decision, not something to discover on the morning of the dig.

The Clay Belt West of the Cliff

Come down off the ridge and the picture reverses. Charmouth Mudstone is a plastic clay. It takes on water in winter and gives it up in summer, and it changes volume as it does so. A dry spell of the sort Lincoln gets fairly regularly, given the city sits at around 600mm of annual rainfall, well under half the UK average, will shrink it noticeably. The following winter puts it back.

Two things follow. First, whatever you build has to be flexible rather than rigid, which is a point in resin bound’s favour over a concrete slab, since a flexible construction rides small movements and a rigid one cracks at them. Second, the stone layer needs to be thicker than it would be uphill. Where 150mm of compacted open-graded stone would do on the limestone, we would generally want 200mm or more on the clay, and more again where anything heavier than a car will stand on it.

The third thing, and the one most often left out, is separation. A geotextile between the clay and the stone stops the two from working into each other. Without it, traffic pumps clay up into the voids, the voids fill, and a drainage layer quietly becomes a wet layer. It is a cheap roll of fabric that decides whether the drive is still draining in ten years.

The Witham Valley and Its Soft Ground

Along the Witham and the Fossdyke, and across a good deal of the lower city, you are on alluvium and river terrace material rather than solid Jurassic rock. It varies over short distances. Silt in one trial hole, sand and gravel in the next, occasionally something soft enough that the digger bucket tells you the answer before you have measured anything.

Where the deposits are gravelly this is decent ground and drains well. Where they are silty it can be poor, and the water table sits high enough that a soakaway is not doing much in winter. That is where a permeable drive stops being a purely permeable design and needs somewhere for overflow to go, which is a conversation about levels and outfalls rather than about resin. Our guide to drains, manholes and inspection covers in a Lincoln driveway goes into how those get handled on site.

Government guidance on permeable surfacing of front gardens is worth a read here, because it sets out plainly what a permeable surface is supposed to achieve and what to do when the ground beneath will not accept the water.

Made Ground: Terraces, Cellars and Old Quarries

Then there is the category the maps do not really cover. Lincoln has been building, quarrying and levelling for two thousand years, and a lot of what sits under front gardens is not natural ground at all. Terraces cut into the slope and backfilled behind retaining walls. Filled-in cellars and coal chutes. Rubble from the 1960s where something older used to stand. Old limestone workings on the higher ground, backfilled at some point by somebody with no reason to record it.

Made ground is unpredictable rather than uniformly bad. Some of it is well compacted and perfectly serviceable. Some of it is voids and half-rotted timber. The only way to know is to open it up, and the honest answer at quote stage is a provisional allowance rather than a fixed price, with an agreed rate for what happens if the ground turns out to be poor.

Be suspicious of a quote that prices a Victorian terrace conversion to the penny without anyone having dug anything. Either they know something you do not, or they have not thought about it and the conversation will happen later, on site, with the digger already hired.

The Layers Themselves, and What Each One Is For

With the ground understood, the build-up itself is straightforward. From the bottom up on a new-build drive: prepared formation, geotextile where needed, compacted open-graded stone, a porous base course, then the resin bound wearing course at roughly 15mm to 25mm depending on aggregate size.

Two details matter more than the numbers. The first is the choice of stone. MOT Type 1 compacts into something close to impermeable because it is graded with fines, which is exactly what you want under a road and exactly what you do not want under a drive designed to drain through. Open-graded stone, whether that is a clean single size or Type 3, keeps the water path open. Guidance from Interpave, the precast concrete paving association, covers permeable pavement design in more depth if you want the engineering behind it.

The second is compaction in layers. Stone laid 200mm deep and whacked once is not a 200mm sub-base, it is a firm top and a loose bottom. Done properly it goes in and gets compacted in lifts, which takes longer and is the first thing to disappear when someone is working to a tight price.

Reading a Quote to See If the Base Was Thought About

You cannot inspect the base once the resin is down. The quote is your only chance to see it, so it should say something. Look for an excavation depth, a description of the stone rather than just the word hardcore, a compacted thickness, whether a membrane is included, what the base course is, and what happens if the ground under your front garden turns out to be worse than expected.

Groundwork is where the price gap between two honest installers opens up, because each has assumed something different about what is down there. Nine times out of ten the higher figure belongs to whoever went and checked. It is also the drive that is still flat in fifteen years.

If you want to know what is under your own front garden before anyone quotes at all, dig a hole in a corner of the lawn, 300mm or so, and look at what comes out. Rock, orange-brown silty clay, grey plastic clay, sand and gravel or a mixture of brick and rubble each point at a different job.

Want to know before you commit? Get a free quote for a resin driveway in Lincoln. We dig a trial hole at the site visit, tell you what your ground actually is, and price the base for that rather than for an average.

Frequently Asked Questions

How deep should the sub-base be under a resin driveway in Lincoln?

On firm ground, which uphill Lincoln usually gives you, 150mm of compacted open-graded stone under a car-only drive is a sound working figure. On the Jurassic clay west and south of the Cliff, or anywhere a van or motorhome parks, 200mm to 250mm is more realistic. Depth is not the only variable though - the stone has to be angular and clean so it locks together and still lets water through, and it has to be compacted in layers rather than tipped and rolled once.

Does Lincoln’s clay ground cause problems for resin driveways?

It causes problems for badly built ones. Charmouth Mudstone and the clays around the lower city shrink in a dry summer and swell again in winter, so anything sitting directly on them moves. The fix is not a thicker slab of concrete, it is a deeper stone layer with a geotextile between the stone and the clay, so the two never mix and the movement is absorbed rather than transmitted straight to the surface.

Can you lay a resin driveway straight onto soil?

No. Resin bound is a wearing surface between 15mm and 25mm thick and it has no structural strength of its own - it does exactly what the layer beneath it does. Laid on soil it will crack, dish and hold water within a season. It needs either a properly built stone and porous asphalt base, or a sound existing concrete or tarmac slab that has been checked over first.

What is MOT Type 1 and why do some Lincoln installers avoid it?

Type 1 is a closed-graded crushed stone with fines in it, designed to compact into something almost impermeable. That makes it excellent under roads and a poor choice under a permeable resin drive, because water passing through the resin then reaches a layer that will not let it go. Open-graded stone, a clean single-size or Type 3, keeps the drainage path open all the way to the ground.

Do I need a geotextile membrane under a resin driveway?

On anything soft, yes. Its job is separation rather than strength. Without it, clay or silt works up into the voids in the stone under traffic and the layer gradually turns from free-draining stone into a sludge that neither drains nor supports. On the alluvium in the Witham valley and on the mudstone west of the Cliff it is not an optional extra.

How can I tell if a Lincoln driveway quote has taken the ground into account?

It will give you numbers. A quote that names an excavation depth, a stone type, a compacted sub-base thickness, whether a membrane is included and what the base course is has been priced against your ground. One that says supply and lay resin bound surfacing and gives a square metre rate has been priced against an average, and your ground may not be average.