Coupage (~ cutting / raping)

Description

The coupage - or finition coupée - (cutting - or cut finish -) gives a flat surface with a stone like texture that captures light very well.
As the plaster begins to set you can start the coupage with the berthelet. If the plaster clings to the berthelet, stop, wait giving opportunity for the plaster to set further before trying again.
Check for bulges on the surface with the rule and eliminate them.
Make sure the entire surface is scraped. Otherwise, unscraped portions will dry significantly lighter often results in a blotchy, unsightly finish that requires a sanding of the entire surface to eliminate.

Select a double sided berthelet as pictured.
Most of the cutting is done later as the plaster sets harder and the grain becomes finer. Often coupages proceeds in two steps: the first fully prepares the surface, the second refines the finish.
In the case of poorly applied coatings, the surface can be first worked by grattage with a nail board then make the coupage as before with the berthelet to refine the finish.