When a client walks into a new commercial warehouse or a residential garage and marvels at a concrete floor that reflects the overhead lights like a mirror, they are looking at a properly "burnished" slab. Achieving this dark, dense, glossy finish is the ultimate test of both the operator's skill and the capability of the walk-behind gasoline power trowel.
Burnishing happens at the very end of the pour. The concrete is now incredibly hard; you can walk on it without leaving any footprint at all. For this final stage, we remove the float pans and transition to specialized finishing blades made of high-carbon spring steel. I pitch the blades to their absolute maximum, almost standing them up on their edges.
Because the concrete is hard, there is very little friction, so I push the gasoline engine throttle wide open, spinning the spider assembly at its maximum speed—often over 130 RPM. The high-speed friction and extreme downward pressure of the pitched steel blades essentially iron the concrete. The heat generated by this friction actually melts the microscopic silica and cement particles together, creating an incredibly dense, non-porous skin. This burnished skin is highly resistant to tire marks, oil spills, and dusting. It requires a heavy machine, a powerful engine, and an operator who knows exactly how to overlap their passes without letting the blades "chatter" or burn the floor.
