Slab-on-Grade
CSI Division 03, Concrete
A concrete floor system poured directly on top of prepared ground, rather than suspended over a crawl space or basement, typically used for the ground floor of a building where the site's soil and drainage conditions support it.
Why it matters
Because it sits directly on the ground, a slab-on-grade's performance depends heavily on what's underneath it: proper soil compaction, a vapor barrier, and adequate drainage all have to be right before the concrete goes down, since fixing a problem underneath a finished slab means breaking it out.
On a real project
Before pouring a warehouse's slab-on-grade floor, the crew compacts the sub-base soil, installs a vapor barrier to block moisture from wicking up through the concrete, and sets reinforcing steel, all inspected before the concrete truck arrives.
Who this matters most to
A Concrete Worker places and finishes the slab itself, but the site prep underneath it, such as compaction, vapor barrier, and reinforcing, is just as critical to the finished product's performance. A Quality Control Manager inspects that sub-slab prep work before the pour, since none of it can be verified once the concrete is down.
Where this goes wrong
A crew pours a slab-on-grade without a vapor barrier to save a day of schedule, assuming the site's soil is dry enough. Months after the building is occupied, moisture wicking up through the slab causes a moisture-sensitive flooring finish to bubble and delaminate, a problem that traces directly back to a step skipped before the pour.