Make Sure The Subgrade is Compacted

Related Links:

Why Build a High Quality Slab on Grade

Make Sure the Subgrade is Compact

Use a Low Water to Cement Ratio– How to Calculate Water to Cement Ratios

Properly Curing Concrete Slabs

The Three Types of Foundations

A case for allowing the time in the schedule to water cure

Special considerations for driveways, walkways, and patios

Be active in deciding where control joints will be placed

The Foundation Construction Process

Preventing Concrete Cracks

Excavations beneath the slab that are not to be filled with concrete (usually plumbing or other mechanical trenches) should be brought back to grade in compacted lifts. This means a 24" trench would be backfilled 6" at a time, each "lift" being mechanically vibrated so it is left compact.

If these excavations are not compacted when backfilled, this loose soil will settle over time leaving the concrete over that area with no earth under it. This becomes a prime place for concrete to settle. Since the soil next to these excavations is native soil, the uncompacted trench can literally become a thoroughfare for water.

Most rental yards have compacting equipment and it is worth the investment to use it.

Excavations from the house to the street for utilities should also be backfilled and compacted in the same manner so areas under the driveway concrete don't sink. Uncompacted areas under lawns can be identified by areas of sunken grass-so it is good idea to compact trenches even under areas not receiving concrete.

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