Definitions for "Scratch coat"
The first coat in plastering; -- called also scratchwork. See Pricking-up.
the first coat of stucco plaster that is scratched with a rake which helps subsequent coats to bond.
Primary thin coat of sand and cement mortar applied to concrete or brickwork to shape and smooth the contours. The surface of this should be scratched with some nails in a piece of wood in order to provide a key for the final render.