Concrete @ your Fingertips

Power-trowel shadow

This appears as a helicopter-blade-like shadow on power-trowelled concrete floor surfaces.  It is caused by leaving the power-trowel on the slab as it cures. Possibly more promenant when left on a floor that has a spray-on curing agent. 

Acknowledgement: Concrete Society

Concrete Bookshop - Members receive 40% discount on Concrete Society publications

Visual Concrete: Control of blemishes