Typical reason for surface dusting after curing and how to prevent?

Typical reason for surface dusting after curing and how to prevent?

• A. Too much curing; prevent by delaying sealing.
• B. Insufficient curing or overfinishing; prevent by proper curing, sealing or densifying, and avoiding excessive abrasion.
• C. Overwatering during finishing; prevent by more aggressive finishing.
• D. Using too fine aggregate; prevent by using coarser aggregate.

Answer: (B)

Dusting on a cured surface happens when the top layer of cement paste is weak or has excess fines, often from not keeping the concrete adequately moist during early curing or from finishing too aggressively after the surface has begun to set. The surface needs moisture to complete hydration and develop a solid, dense laitance that won’t powder off. If finishing is too harsh or performed too soon, fines and weak paste are pushed to the surface, creating a powdery layer that dusts off. Prevention centers on two things: first, proper curing to maintain moisture long enough for the paste to hydrate and gain strength; this can involve curing compounds, wet blankets, fogging, or plastic sheets. Second, after curing, hardening the surface through sealing or densifying helps resist dusting, and you should avoid excessive abrasion during finishing by using appropriate timing and less aggressive tools. The other options don’t address the root cause—either they misstate what causes the dusting or suggest remedies that don’t effectively prevent it.

Dusting on a cured surface happens when the top layer of cement paste is weak or has excess fines, often from not keeping the concrete adequately moist during early curing or from finishing too aggressively after the surface has begun to set. The surface needs moisture to complete hydration and develop a solid, dense laitance that won’t powder off. If finishing is too harsh or performed too soon, fines and weak paste are pushed to the surface, creating a powdery layer that dusts off.

Prevention centers on two things: first, proper curing to maintain moisture long enough for the paste to hydrate and gain strength; this can involve curing compounds, wet blankets, fogging, or plastic sheets. Second, after curing, hardening the surface through sealing or densifying helps resist dusting, and you should avoid excessive abrasion during finishing by using appropriate timing and less aggressive tools. The other options don’t address the root cause—either they misstate what causes the dusting or suggest remedies that don’t effectively prevent it.