A plate compactor is primarily a dirt tool, but its role in municipal asphalt patching is absolutely critical. However, if you take a standard dirt plate and drop it directly onto fresh Hot Mix Asphalt (HMA), you are going to create a catastrophic mess. Asphalt at 150°C [approx. 300°F] is incredibly sticky. The hot bitumen will instantly bind to the cold steel base plate. Within three passes, your flat plate will be caked in a thick, jagged layer of hardened tar, which will then tear the tender asphalt mat to shreds, ruining your finish and destroying the structural integrity of the patch.
To use a gasoline plate compactor on blacktop, it must be equipped with a high-capacity water suppression system. Commercial asphalt plates feature a heavy-duty polyurethane tank mounted directly above the engine, holding anywhere from 10 to 15 liters [approx. 2.6 to 4 gallons] of water. This tank feeds a drip bar positioned across the front of the base plate. Before I ever touch the hot mat, I open the petcock and ensure a steady, even sheet of water is coating the entire steel plate. The water acts as both a thermal barrier and a non-stick lubricant.
There is an art to it, though. If you flood the plate, the excess water will rapidly cool the top layer of the asphalt, creating a brittle crust while the material beneath remains soft, leading to immediate surface cracking. You need just enough water to keep the steel slick. Furthermore, the edges of the base plate on a dedicated asphalt machine are slightly curved or radiused. A sharp, 90-degree square edge will dig into the hot asphalt every time you turn the machine, leaving deep gouges. A radiused edge glides over the "slump" of the asphalt, leaving a tight, glass-smooth finish that seamlessly ties into the existing roadway.
