Which of the following is not a characteristic of "flashing"?

Flashing refers to a specific application technique used to enhance the surface quality and performance of refractories. The characteristic that identifies flashing is that it is applied after the initial setting of the refractory material.

When discussing the options provided, choosing to apply flashing before the refractory is set contradicts the very definition and purpose of flashing. The essence of flashing is to provide an additional layer or coating that acts upon an already set refractory surface, allowing for improvements in physical properties or visual aspects through methods such as gunning or troweling. This practice can help in areas that may have imperfections or where a more refined surface is needed for enhanced durability or performance.

The other characteristics highlight how flashing is distinctly utilized over existing refractory material rather than as an initial layer. It emphasizes the timing of application in relation to the setting phase of refractories, reinforcing the idea that flashing is meant for post-set application, which makes the incorrect choice about its timing evident.