The exposed aggregate specification

Standard

Work is carried out with reference to AS 3727.1, the Australian Standard for residential pavements. At the crossover, the section between your boundary and the road, each council's nominated standard drawing governs, and Melbourne's eastern councils each publish their own. Where a council drawing and this page differ at the crossover, the council drawing wins.

Preparation and base

The existing surface is removed and the area prepared to suit the ground: soft spots and organic material taken out, and compacted base material brought in where the site needs it. Much of Melbourne's east sits on reactive clay that swells in winter and shrinks through summer, and the base and drainage do more for the life of a slab on that clay than any amount of extra concrete. Sandy bayside blocks drain faster but still need proper compaction.

Membrane and reinforcement

A membrane is laid where the site requires it, and every slab is reinforced with steel mesh placed on chairs so the steel sits within the slab and can do its job.

Concrete and the decorative mix

Driveways are poured at a minimum of 25 MPa. The decorative mix is designed before the truck is booked: stone type and size, 7mm, 10mm or 14mm, the blend proportions, and the oxide that colours the cement paste, all confirmed from the samples viewed on site. The mix is ordered from the batching plant to that design, because the stone cannot be changed once it is in the truck. The colours and stone guide covers the choice itself.

Joints

Control joints are cut to direct any movement to planned lines, with isolation joints against the garage slab, house footings and existing concrete where needed. On exposed aggregate the joint layout is agreed before the pour, because joints read as part of the finished pattern.

Drainage and fall

Every surface is set with a fall away from the house. Where a block falls towards the garage, a grated strip drain is formed in across the threshold and connected to stormwater rather than left as someone else's problem. Patios and alfresco areas fall away from the building line, and pool surrounds fall away from the water.

Crossovers

The crossover is built to the council's standard drawing. Most eastern councils require a vehicle crossing permit before the crossover is touched, and several inspect the boxing before the pour. Which permit and inspections your job needs is identified at the site measure and confirmed in writing with the quote; council application fees belong to the council and are not part of the quoted price.

The exposed aggregate process

This is the section that separates the finish from plain concreting, and it is where the job is won or lost.

Placement. The decorative mix is poured and screeded like any structural slab, then finished only as far as the surface needs: overworking the top drives stone down and paste up, and the stone is the point.

Surface retarder. As soon as the surface is ready, a chemical retarder is applied across the top. It holds the top few millimetres of cement paste soft while the body of the slab cures hard underneath.

The wash-off. Hours later, inside a window that moves with the weather, the day's temperature and the mix, the soft paste is washed away under controlled pressure to reveal the stone evenly across the whole surface. Wash timing is the single point where the finish is won or lost: too early and stone tears out of the surface, too late and the paste locks in and no pressure will move it. The pour day is planned backwards from this window, which is why pour times move with the forecast.

Cure. After the wash, the slab is kept curing. Vehicles stay off a new driveway for seven days as a guide, foot traffic sooner.

Sealing. Once the surface has cured and dried it is sealed, penetrating or film as agreed at quote, with a grip additive in film systems on slopes. The sealing guide explains the choice, and the reseal interval, three to five years as a working guide, is put in writing at handover.

What this means for a quote

If a competing quote is materially cheaper, the difference is usually in the preparation, the mesh, the mix design or the crew's wash-off discipline, and only the first three can be checked on paper. Ask for the base, the mesh and the mix in writing and compare them against this page, the cost guide and the calculator. Then ask who does the washing, because that is the part you will look at for twenty years.