True or False: Vibrating sticky concrete should be avoided because it tends to bring excessive fines to the surface.

True or False: Vibrating sticky concrete should be avoided because it tends to bring excessive fines to the surface.

• A. True
• B. False
• C. Not sure
• D. It depends

Answer: (B)

Vibration is a tool to consolidate concrete and push out trapped air. In a sticky, cohesive mix, the paste and fines are already well bonded, so vibration does not inherently drag excessive fines to the surface. The surface problem most often tied to fines comes from bleeding (water rising) and too wet a mix, which can create laitance if finished too early or too aggressively. With a sticky mix, bleeding is typically limited, and proper timing of vibration and finishing helps achieve a dense, uniform surface without an excess skim of fines. So, vibrating sticky concrete is not something you should avoid solely because it brings fines to the surface; when used correctly, vibration aids proper consolidation and surface quality.

Vibration is a tool to consolidate concrete and push out trapped air. In a sticky, cohesive mix, the paste and fines are already well bonded, so vibration does not inherently drag excessive fines to the surface. The surface problem most often tied to fines comes from bleeding (water rising) and too wet a mix, which can create laitance if finished too early or too aggressively. With a sticky mix, bleeding is typically limited, and proper timing of vibration and finishing helps achieve a dense, uniform surface without an excess skim of fines. So, vibrating sticky concrete is not something you should avoid solely because it brings fines to the surface; when used correctly, vibration aids proper consolidation and surface quality.