When we do heavy-duty industrial floors or high-end stamped concrete, we often use "dry shake" color hardeners or metallic surface hardeners. These are fine powders broadcast over the surface of the wet concrete to create a heavily armored, colored skin. The only way to successfully integrate these powders into the slab is through the brutal, mechanical force of a gasoline power trowel.
If you just throw the powder on and try to hand-trowel it, the powder will just sit on the surface, eventually delaminating and peeling off under forklift traffic. The technique requires timing and raw machine weight. We broadcast the powder right as the bleed water disappears. Then, I drop the walk-behind trowel onto the slab equipped with a wide float pan. The pan does not cut the concrete; instead, the massive weight of the machine combined with the rotational friction forces the dry powder deep into the wet cement paste.
The commercial gas engine will audibly bog down during this process because the dry shake sucks the moisture out of the surface, turning the mud incredibly stiff and sticky. We have to make multiple passes—broadcast, pan, broadcast, pan—until the surface is a uniform color and the hardener is fully wetted out by the slab's internal moisture. Only then do we pull the pan off and use the finishing blades to close it up. The power trowel isn't just a smoothing tool here; it is the mechanical press that manufactures the armored skin of the floor.
