What Sub Base Does a Resin Driveway Need?
Updated: 3 days ago
A resin bound driveway has to go on a solid, bound base: either a new build of compacted stone sub-base topped with tarmac (porous asphalt if you want it to drain) or concrete, or an existing tarmac or concrete drive that is sound, level and not cracked. It cannot go straight onto loose stone, soil, block paving or slabs. The resin is only around 18mm thick on a drive, so the base does all the structural work.
Why the base matters more than the resin
Resin bound is a wearing course, not a structure. It is slightly flexible, it binds the stone together, and it drains if what is under it drains. But it copies every movement, crack and dip in the layer below. Most cracked or sunken resin drives have a base problem, not a resin problem, which is why the base comes first in any answer to are resin driveways any good.
That is why two quotes from resin bound driveway installers for the same drive can differ so much: one may include digging out and building a proper base, the other may be pricing an overlay on whatever is there.
Option 1: a new permeable base
This is the full build, and the only one that gives you a driveway that drains straight through.
Dig out the old surface and soil to the depth the build needs.
Geotextile membrane over the formation, to separate the stone from the ground.
Open-graded sub-base. A clean, no-fines stone such as MOT Type 3 or a 4/20 aggregate, compacted in layers. The government's permeable front gardens guidance describes about 150mm of sub-base laid over the geotextile and compacted, and explains that these open-graded materials have space between the stones to store water.
Porous asphalt binder course. One resin supplier's guidance, for example, gives 50mm of 14mm porous close-graded macadam, over a well-compacted Type 3 sub-base.
Edging fixed and set slightly proud of the base, so the resin finishes flush against it.
Resin bound surface, trowelled at around 18mm for a driveway.
Our resin bound driveway in Claregate is an example of this kind of build: laid over an open-grade tarmac base with Type 3 stone and finished with Daltex resin.
Why not Type 1? Standard MOT Type 1 contains fine material that compacts into a dense, tight layer. Interpave, the precast paving trade body, notes that Type 1 is not permeable when compacted. Under resin that is meant to drain, it defeats the point.
Option 2: a new non-permeable base
A new base of dense tarmac over a Type 1 sub-base, or a concrete slab, is also a sound substrate for resin. Pavingexpert's guidance for one major resin system names a minimum 50mm compacted layer of 14mm or smaller dense bitmac as the preferred substrate for driveways; one supplier's concrete option is 100mm of C25 smooth brushed concrete, fully cured and primed before the resin goes on.
The catch is drainage. Water cannot pass through a solid base, so the drive needs falls and somewhere for the water to go: a channel drain, a soakaway, or a lawn or border.
Option 3: overlaying existing tarmac or concrete
Can you lay resin over tarmac? Yes, if the tarmac is sound: firm, not crumbling, not rutted, roughly level and well bonded. Minor level variation can be taken up in the resin layer; significant dips should be corrected with bituminous material first.
Can you lay resin over concrete? Yes, on the same terms: solid, not cracked or lifting, clean and primed. Cracks in the old slab are the main risk, because they reflect up through the resin. Supplier guidance calls for cracks to be treated (for example with a cross-layer membrane) and badly damaged areas to be broken out and reinstated before overlaying.
Either way, the surface must be completely dry and thoroughly cleaned, and there must be an edge for the resin to finish against.
The planning catch with overlays
In England, a new or replacement hard surface over 5 square metres in a front garden needs planning permission unless it is permeable or drains to a lawn or border (see the government guidance on permeable front gardens). Resin over solid tarmac or concrete is not permeable as a whole, however porous the resin layer is. So an overlay on a front drive needs its water directed onto a lawn, border or soakaway, or it falls outside permitted development. A new permeable base avoids that problem entirely.
Resin over block paving or paving slabs
The short answer is usually no. Block paving and slabs are separate units on a bed of sand or mortar, and each one moves slightly on its own. Pavingexpert warns that these elemental pavings are usually not suitable under resin because of reflective cracking: the joint pattern comes up through the resin as a grid of cracks.
Overlaying very well-bedded block paving is sometimes attempted. It is a risk, and if it fails there is little you can do except take the lot up. Lifting the blocks and building a proper base is the reliable route.
When an existing base is too far gone
Signs that an old drive cannot be overlaid:
Cracks wider than a hairline, or cracks that move when you drive over them.
Ruts, dips or sunken areas, especially in the wheel tracks.
Crumbling or loose tarmac, with stone coming away.
Rocking slabs or uneven blocks.
Water standing where it has nowhere to go, if the new drive needs to drain.
Levels at the house that would bring the finished surface too close to the damp proof course.
If the old base fails on any of these, overlaying just postpones the problem. The resin will copy the defect within a season or two.
How deep is a resin driveway build?
There is no single legal depth for a driveway; it depends on the ground, the traffic and the system. As a guide, a full permeable build is the sub-base (the government guidance describes about 150mm), plus a porous asphalt layer, plus around 18mm of resin. Our Pendeford resin driveway was laid over 100mm of permeable base. Soft or clay ground and heavier vehicles can call for more.
Resin base questions, answered
Does the base affect the price much?
More than anything else. Our post on whether resin driveways are expensive explains why overlay and new-build quotes are so far apart.
Is the base the same for a patio?
The principles are the same, but foot traffic needs a lighter build and a thinner resin layer (about 15mm). Our resin patio post covers patio bases.
Can resin go on a gravel or MOT surface?
Not directly. Loose or unbound stone needs a bound layer of porous asphalt or concrete on top before resin bound goes down, except for specialist tree-pit systems.
Pete and the team will tell you at a free site visit around Wolverhampton whether your existing drive can be overlaid or needs a new base, and price it accordingly. If a rigid finish suits the ground better, exposed aggregate driveways are the other option to compare.
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