Which coat is applied directly to the prepared surface to establish bonding with the substrate?

Which coat is applied directly to the prepared surface to establish bonding with the substrate?

• A. Finish coat
• B. Scratch coat
• C. Brown coat
• D. Bonding coat

Answer: (D)

The main idea is that the bonding coat is the layer that grabs onto the substrate and forms the initial adhesion for the plaster system. It’s applied directly to a properly prepared surface so the plaster can bite into it and create a reliable bond with whatever is underneath, whether it’s concrete, masonry, or a prepared substrate on lath. This coating often includes bonding agents and is slightly rough or keyed to give the next coats something to grip. The other coats have different roles: the scratch coat (the first built-up layer above the bonding coat) provides a rough key for the next layer; the brown coat adds bulk and strength; the finish coat is the thin, final layer that gives the smooth, finished surface.

The main idea is that the bonding coat is the layer that grabs onto the substrate and forms the initial adhesion for the plaster system. It’s applied directly to a properly prepared surface so the plaster can bite into it and create a reliable bond with whatever is underneath, whether it’s concrete, masonry, or a prepared substrate on lath. This coating often includes bonding agents and is slightly rough or keyed to give the next coats something to grip.

The other coats have different roles: the scratch coat (the first built-up layer above the bonding coat) provides a rough key for the next layer; the brown coat adds bulk and strength; the finish coat is the thin, final layer that gives the smooth, finished surface.