Which practice is most associated with preventing surface blisters during finishing?

Which practice is most associated with preventing surface blisters during finishing?

• A. Keep float blades flat and delay troweling as long as possible
• B. Trowel as soon as possible with a high-angle blade
• C. Use a rough float and finish immediately
• D. Add extra water to the surface

Answer: (A)

Preventing surface blisters comes from controlling moisture and trapped air as you finish. Using a flat float blade to smooth the surface keeps the top layer from digging in or pushing water and air around, delivering a uniform, gentle finish. Waiting to trowel until the surface has started to stiffen allows the bleed water to rise and evacuate rather than being sealed under a newly compacted film. Finishing too soon with a high-angle blade or using a rough float can trap air and moisture beneath the surface, creating pockets that form blisters as the concrete continues to hydrate. Adding extra water only supplies more surface water, increasing the risk of trapped moisture and blistering.

Preventing surface blisters comes from controlling moisture and trapped air as you finish. Using a flat float blade to smooth the surface keeps the top layer from digging in or pushing water and air around, delivering a uniform, gentle finish. Waiting to trowel until the surface has started to stiffen allows the bleed water to rise and evacuate rather than being sealed under a newly compacted film. Finishing too soon with a high-angle blade or using a rough float can trap air and moisture beneath the surface, creating pockets that form blisters as the concrete continues to hydrate. Adding extra water only supplies more surface water, increasing the risk of trapped moisture and blistering.