What is the typical bond strength challenge when plastering over smooth concrete?

What is the typical bond strength challenge when plastering over smooth concrete?

• A. It bonds easily with no additives
• B. It cannot be plastered
• C. It requires only a primer
• D. It requires bonding agent and possibly a scratch or bond coat to ensure adhesion

Answer: (D)

Bond strength when plastering over smooth concrete is weak because the surface is non-porous and lacks a mechanical key for the plaster to grab onto. To make adhesion reliable, you need to establish both chemical and physical bonding. A bonding agent helps the plaster chemically adhere to the concrete, while a scratch coat (or bond coat) roughens the surface to create a mechanical key and better suction for the plaster to grip. That combination—bonding agent plus a scratch or bond coat—is what actually ensures the plaster will adhere over smooth concrete. Relying on a primer alone isn’t enough, and saying it bonds easily with no additives or that it cannot be plastered ignores the practical prep steps that make adhesion possible.

Bond strength when plastering over smooth concrete is weak because the surface is non-porous and lacks a mechanical key for the plaster to grab onto. To make adhesion reliable, you need to establish both chemical and physical bonding. A bonding agent helps the plaster chemically adhere to the concrete, while a scratch coat (or bond coat) roughens the surface to create a mechanical key and better suction for the plaster to grip. That combination—bonding agent plus a scratch or bond coat—is what actually ensures the plaster will adhere over smooth concrete. Relying on a primer alone isn’t enough, and saying it bonds easily with no additives or that it cannot be plastered ignores the practical prep steps that make adhesion possible.