When should the slab be placed after subbase placement?

• A. After 24 hours
• B. After 3 days
• C. It depends on weather
• D. As soon as possible

Answer: (D)

Placing the slab as soon as possible after the subbase is prepared keeps the bearing surface stable and consistent. Once the subbase is compacted and finished, delaying the pour allows moisture loss, dust, or surface contamination to alter its density and profile, which can lead to uneven support and potential cracking in the slab. Pouring promptly helps ensure the subbase and slab cure together under similar conditions, reducing the risk of differential movement between layers. If weather or other conditions require tweaks, you still aim to avoid unnecessary delays and protect the site, but the preferred approach is to pour as soon as the subbase is ready.