How long should you wait to backfill after pouring your concrete foundation?

Short answer: at least 28 days.

Long answer:

It’s common in the construction industry to backfill a few days after pouring foundation walls. The foundation of a home not only holds the house up, but should keep moisture out, insulate from the cold, and resist the earth’s movement around it. It provides stability to the structure above it and prevents uneven settling. There’s a lot of weight on the foundation of a house, both literally and figuratively. 

Backfilling too early adds pressure to the concrete before it has had a chance to fully cure. Under ideal conditions, it takes 5-7 days for concrete walls to cure to 75%, and 28 days to be fully cured. Backfilling quickly might seem like a good idea when you’re concerned about deadlines and moving a project forward, but you only get one chance to get the foundation right. Backfilling too early can cause micro-fractures in the foundation and major problems in the future. 

The foundation of a home should be durable - it should last the next century or longer. Starting out with micro-fractures sets the foundation up for failure. The long term durability that comes from waiting the full 28 days for your foundation to cure creates benefits that far outweigh any benefits from backfilling a few weeks earlier.