Q.: What does the term shingling mean when describing vertical slipformed concrete?

A.: We asked slipforming consultant Leon Bialkowski to define the term. He says that the typical slipform is 4 feet high and constructed with a slight batter (1/8 to 1/4 inch) so it will be self-clearing as it slides. This makes the top of the forms slightly smaller and the bottom of the forms slightly larger than the required wall thickness. The combined effects of a full head of concrete and vibration used for consolidation can create a pressure that pushes the bottom out even further. This results in a horizontal offset that resembles shingles on a house.

In a 1973 technical report from the Cement and Concrete Association of Australia, author J. O'Brien says shingling is generally noticed at planned stops where forms have been removed at the end of the day to prevent binding. The taper on the forms leaves a slight gap between the face of the concrete and that of the form. The added effect of concrete pressure as the forms are filled the next day may increase this gap, resulting in a slight step in the wall thickness. This stepping plus the associated grout loss are particularly undesirable when special architectural effects are required.