You are finishing a concrete surface; defects such as crazing, dusting, and spalling are caused by which condition?

You are finishing a concrete surface; defects such as crazing, dusting, and spalling are caused by which condition?

• A. not working the surface enough
• B. waiting too long to start the floating process
• C. improper consolidation
• D. overworking the concrete surface

Answer: (D)

Overworking the surface during finishing creates a weak, paste-rich layer at the top of the concrete. When you keep troweling after the surface has stiffened, you push cement paste and fines toward the surface and drive out bleed water, forming this thin laitance. That weak outer layer can wear away easily and leads to defects like crazing (fine surface cracks from shrinkage and rapid drying), dusting (powdery surface where the weak paste is removed), and spalling (surface flakes when the weak layer is stressed or exposed to freezing and impact). The other finishing actions described in the options don’t produce that thin, weak surface layer in the same way, so overworking is the primary cause of these surface defects.

Overworking the surface during finishing creates a weak, paste-rich layer at the top of the concrete. When you keep troweling after the surface has stiffened, you push cement paste and fines toward the surface and drive out bleed water, forming this thin laitance. That weak outer layer can wear away easily and leads to defects like crazing (fine surface cracks from shrinkage and rapid drying), dusting (powdery surface where the weak paste is removed), and spalling (surface flakes when the weak layer is stressed or exposed to freezing and impact). The other finishing actions described in the options don’t produce that thin, weak surface layer in the same way, so overworking is the primary cause of these surface defects.