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Site Preparation and Placement Environment for Commercial Floors

All concrete slabs-on-ground require good subbgrade or base beneath to support the concrete. But note that the critical thing is uniform support. Soft spots are the death of any slab. Here are a few things to keep in mind about the subgrade (the ground beneath the slab) and the subbase (an optional compacted gravel layer between the concrete and the subgrade):

Good compaction and grading of the
subbase is essential to a good floor. Daniel Dorfmueller

Grading of the subgrade—or rough grading--should meet a tolerance of +0 inch/–1½ inches. Get a rod and level survey done to make sure the subgrade complies with this tolerance before the excavation equipment is taken off site. Take measurements at 20-foot intervals in two perpendicular directions.
Base tolerances—or fine grading--should meet a tolerance of +0 inch/–1 inch for floor Classes 1 to 3 and +0 inch/–3/4 inch for floor Classes 4 to 9. This elevation is measured from the specified bottom of the slab.
The base material should be compactable, easy to trim, granular fill that will remain stable and support construction traffic. To test this, perform proof rolling on a grid pattern for the entire slab area.


When proof-rolling reveals soft spots like these, recompaction is necessary. Daniel Dorfmueller

Proof-rolling is the most effective ways to determine if the soil-support system will provide uniform and adequate bearing support during construction and for the life of the slab. Proof rolling involves driving a fully loaded dump truck or ready mix truck across the subgrade or subbase. If any of the wheels sink in deeper than ½ inch, that area will need to be recompacted.
Vapor barriers are essential beneath most interior concrete floors, especially if there is any intention of installing moisture-sensitive floor coverings (tile, wood, vinyl, etc.). In general, the vapor barrier should be directly beneath the concrete. Learn more about vapor barriers.
Learn more about subgrades and subbases.
Whenever possible, install floor slabs in a controlled environment. Ideally the roof should be on and the walls in place—protecting the soil support system and the concrete slab from wind, rain, sun, and extreme temperatures will greatly improve the slab. Learn more about cold weather techniques and hot weather techniques.