How Is Imprinted Concrete Laid? From Dig-Out to Sealer

Laying imprinted concrete splits into two very different halves. The first is ordinary groundwork: dig out, build and compact a stone sub-base, set up forms to the right falls. The second is a race against the concrete setting: pour, level, trowel in a colour hardener, spread a release agent and stamp the pattern with rubber mats, all within a few hours on the same day. Then come the slower jobs: cutting joints, washing off and sealing.

Here's what happens at each stage when we lay pattern imprinted concrete driveways on a typical home, and what to look for if you're watching it happen on yours.

Stage 1: Survey, levels and drainage

Before anything is dug, the levels are set. Concrete isn't permeable, so every drop of rain has to run off the surface to somewhere useful.

• Falls away from the house. LABC Warranty guidance is a fall of no less than 1:80 and no more than 1:12 away from the building.

• Below the damp course. The finished surface should sit at least 150mm below the damp proof course.

• Where the water goes. A lawn or border, a gully, or a channel drain across the entrance. On a front garden in England over 5 square metres, run-off has to go to a permeable area on your property for the work to be permitted development.

Get this stage wrong and nothing that follows can fix it.

Stage 2: Dig-out and sub-base

The old surface and soil come out to the depth of the sub-base plus the slab. For a car driveway on decent ground that's at least 200mm below finished level, more on clay.

The sub-base is crushed stone, compacted in layers with a plate or roller. LABC gives 100mm as the minimum for a light-duty drive and 150mm for medium duty. Pavingexpert's guidance for imprinted concrete is to level the formation to within plus or minus 12mm, because every dip becomes a thin spot in the slab.

On many jobs a damp proof membrane goes down over the sub-base so the stone doesn't suck water out of the fresh concrete.

Stage 3: Forms, mesh and joints planned

Timber or steel forms are fixed around the edges to the exact finished levels and falls. Isolation strips go against the house and any walls so the slab can move without pushing on the building. Where reinforcement is going in, mesh is set on spacers so it sits in the slab, not on the ground.

This is also when the joint layout gets planned: where the sawn control joints will run so they fall on pattern lines and split the drive into sensible bays. LABC limits in-situ bays to 20 square metres and 6m long.

Stage 4: The pour

Ready-mixed concrete arrives by lorry, or by dumper or pump where access is tight. Pavingexpert describes typical imprinted mixes as fairly high strength, with small (10mm) aggregate and polyester fibres to reduce micro-cracking.

The slab goes in at full depth (100mm minimum for cars, 150mm on poor ground or clay), is levelled off the forms and floated flat. From here the clock is running.

Stage 5: Colour hardener

A powdered colour hardener is broadcast by hand over the wet surface, about 1.5kg per square metre according to pavingexpert, in more than one pass. It soaks up moisture from the concrete and is trowelled in, creating a dense, coloured, hard-wearing top layer a few millimetres thick. This is where your chosen base colour comes from.

Stage 6: Release agent and stamping

A release agent goes on next, in a contrasting colour, at about 200g per square metre. It stops the mats sticking and leaves darker tones in the grooves, which is what gives the pattern its depth.

Then the stamping. Rubber mats (from about 300x300mm up to 900x900mm) are laid in sequence and tamped into the surface, with flexible "floppy" mats and hand tools for the edges, corners and around drains. The timing is everything: too early and the pattern slumps; too late and it won't take. A border in a different pattern or colour is stamped at the same time.

This is why imprinted concrete is not a DIY job. Colour, release and stamping on a whole drive have to be done by an experienced team in one window that the weather and the mix set, not the clock.

Stage 7: Wash off and seal

Between 24 and 96 hours after the pour, the surface is washed down to remove the excess release agent. That reveals the final two-tone colour. Once the slab is dry, one, preferably two, coats of clear acrylic sealer go on. The sealer locks in the colour and keeps oil and water out, and it's the part that will need renewing every few years. Forms come off after 3 to 7 days in pavingexpert's guidance.

Stage 8: Cutting the joints

On residential drives the control joints are usually sawn at the end of the job, a week or more after sealing, once the concrete has cured enough not to spall at the cut edges. They run along pattern lines where possible, to a quarter to a third of the slab's depth. Pavingexpert's rule of thumb is a joint roughly every 30 times the slab thickness, so about every 3m on a 100mm slab.

Stage 9: Handover

Foot traffic is usually fine after a day or two. Pavingexpert puts an imprinted drive as safe to traffic usually 4 to 7 days after laying, so plan for a week off it; our post on how long concrete takes to dry explains the curing times in detail. Heavy vehicles wait 28 days.

Imprinted concrete process questions, answered

How long does the whole job take?

It depends on the size, the dig-out and the weather. The pour and stamping are a single day; the groundwork before and the washing, sealing and curing after take the rest.

Can it be laid in winter?

Not in frost. Fresh concrete must not freeze, so pours are planned around the forecast. Cold, damp weather also slows washing off and sealing.

What's different about exposed aggregate?

The groundwork and slab are the same. Instead of colour and stamping, a surface retarder is sprayed on and the top layer washed away the next day to reveal the stones; see exposed aggregate concrete.

Every imprinted drive Drive Tech lays in Wolverhampton goes through these stages with our own team, from breaking out the old surface to the final coat of sealer. The groundwork and slab are the bulk of the price, which our concrete driveway cost post breaks down.