What is the meaning of "keying" a plaster surface?

• A. Creating a smooth finish
• B. Creating a roughened surface or grooves to improve adhesion between coats
• C. Applying waterproofing
• D. Painting with key pigments

Answer: (B)

Keying a plaster surface means roughening it to give the next layer something to grip. The “key” is the rough texture—grooves or scratches—that creates a mechanical interlock between coats, so the finish adheres strongly and won’t pull away as it dries and moves. This is usually done on the base coat or when applying new plaster over an existing surface by scratching or scoring with a trowel, comb, or other tool to leave shallow lines or a roughened texture. It’s about improving adhesion, not making a smooth finish, applying waterproofing, or painting.