What finish should a slab on grade have if used for a casting platform?

• A. Hard Trowel
• B. Float finish
• C. Broom finish
• D. Exposed aggregate

Answer: (A)

A casting platform needs a hard, very smooth surface to cast concrete panels cleanly. A hard trowel finish creates a dense, low-porosity bed with minimal surface roughness, which helps the panel bottom seat evenly, releases easily from the bed, and avoids imprinting flaws or voids into the underside. It also resists sticking and damage during stripping.

A float finish is smoother than a broom finish but still has enough texture to create surface irregularities. A broom finish intentionally leaves ridges for slip resistance, which would transfer to the panel bottom and hinder proper release and flatness. Exposed aggregate introduces visible stones and a rough texture that would mar the panel underside and complicate demolding. Hence, the hard trowel finish is the best choice for a casting platform.