Where should the gap be measured when using a straightedge to check flatness?

Where should the gap be measured when using a straightedge to check flatness?

• A. In the middle.
• B. At the edge.
• C. At a corner.
• D. At the joint.

Answer: (A)

When checking flatness with a straightedge, the gap is read where the straightedge spans the surface and the potential deviation is most pronounced. With the straightedge supported at its ends, any dip in the concrete shows up as the largest gap at the midspan. Measuring in the middle therefore gives the best indication of flatness across the panel. Edges, corners, or joints can be influenced by formwork, finishing, or construction features and don’t reflect the overall flatness as reliably.

When checking flatness with a straightedge, the gap is read where the straightedge spans the surface and the potential deviation is most pronounced. With the straightedge supported at its ends, any dip in the concrete shows up as the largest gap at the midspan. Measuring in the middle therefore gives the best indication of flatness across the panel. Edges, corners, or joints can be influenced by formwork, finishing, or construction features and don’t reflect the overall flatness as reliably.