If blisters form, which step is recommended for surface repair before further finishing?

If blisters form, which step is recommended for surface repair before further finishing?

• A. Flatten the trowel blades or reopen the surface with a wood float and delay finishing
• B. Increase troweling pressure with the same blades
• C. Sand the surface aggressively and continue finishing
• D. Apply sealer over the blistered area and finish

Answer: (A)

When blisters appear, the surface must be reopened and flattened to remove the trapped air and any excess moisture before finishing. Using the trowel blades to flatten the surface or reopening the area with a wood float helps level the ridges and break the blister skin, bringing the paste back into the pores and creating a uniform surface. Then delay finishing so bleed water can dissipate and the concrete can recompact, reducing the risk of finish defects like pinholes or scaling. Why not push more trowel pressure, sand aggressively, or seal over the blistered area? Increasing pressure can push air and moisture deeper and worsen the problem; aggressive sanding may tear the surface and leave an uneven or damaged finish; applying a sealer over a blister traps moisture and can lead to later cracking or delamination.

When blisters appear, the surface must be reopened and flattened to remove the trapped air and any excess moisture before finishing. Using the trowel blades to flatten the surface or reopening the area with a wood float helps level the ridges and break the blister skin, bringing the paste back into the pores and creating a uniform surface. Then delay finishing so bleed water can dissipate and the concrete can recompact, reducing the risk of finish defects like pinholes or scaling.

Why not push more trowel pressure, sand aggressively, or seal over the blistered area? Increasing pressure can push air and moisture deeper and worsen the problem; aggressive sanding may tear the surface and leave an uneven or damaged finish; applying a sealer over a blister traps moisture and can lead to later cracking or delamination.