A. The forms should remain in place for at least 8 to 12 hours after the wall is poured, if the temperature is above 50° F. You can begin laying your sills and joists, and building light frame walls, immediately thereafter. But avoid backfilling or other work that places a lot of stress on the foundation walls, for at least seven days after the pour. By this time, the concrete should reach 80% of its ultimate strength. If the concrete is placed in cold weather, you should wait longer before building and backfilling to compensate for the delay in the setting reaction.

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