What spray sealing actually involves

A spray seal is a thin layer of bituminous binder sprayed onto a prepared pavement, with a single-sized aggregate rolled into it while the binder is still hot. It is not asphalt. It has no structural depth of its own. What it does is keep water out of the pavement underneath and give tyres something to grip, and across regional Australia it is by far the most common sealed surface on the road network.

The process looks simple from the roadside. The sprayer runs a bar of nozzles across the surface at a set rate, the aggregate truck follows and spreads stone, and the rollers seat it. Then the sweepers come through and lift the loose. What you cannot see is how much has to be right for it to hold: the binder application rate for that aggregate size and that traffic, the surface temperature at the time of spraying, the moisture in the stone, and the rolling window before the binder cools.

Get any of those wrong and the seal strips within a season. Too little binder and the stone plucks out under traffic. Too much and it bleeds in summer, flushing to the surface and losing its texture. Spray on a cold pavement and the binder never wets the aggregate properly in the first place.

That is why we run spray seal as its own discipline rather than a job the asphalt crew does when there is a gap. Primer seals to new pavements, reseals to existing networks, and sealed surfaces under sporting courts are each different problems, and the planning is where most of them are solved. On a subdivision, that means sequencing the seal so the last house lot does not get built on top of it. On a rural network, it means reading the weather three days out and being honest with the client when the window has closed.