What Do You Put Down Before Laying Concrete? (Kansas City Base Prep Guide)

The layer beneath your slab determines whether it stays flat and crack-controlled or settles and scales. In Kansas City—with expansive clays, spring storms, and freeze–thaw—subbase design matters as much as the concrete mix. Here’s exactly what to put down before you pour, and why it pays off for decades.

Remove organics, topsoil, and soft spots until you reach undisturbed, competent subgrade. Proof-roll (drive or compact) to identify pumping or deflection. If the ground yields beneath your feet, it will yield under the slab.

On particularly soft or wet clays (common in parts of KC, Gladstone, and Raytown), roll out a nonwoven geotextile before placing base stone. It spreads load and prevents your aggregate from sinking into the mud during compaction.

For basements, garages receiving coatings, or interior shop slabs, install a vapor retarder directly beneath the slab to protect finishes and reduce moisture transmission. Discuss a blotter layer (thin sand) with your contractor only if specified to balance curl vs. moisture control.

Set forms square and true with string lines or laser. Target slope 1/8–1/4 inch per foot away from structures. Plan transitions at doors, garages, and sidewalks to avoid puddles and trip points. Extend downspouts so runoff doesn’t saturate slab edges—the first area to spall in winter.

Install rebar on chairs (not laid on dirt) with ties and proper spacing—often #3/#4 bars at 18–24" for residential slabs. Dowel through thresholds and construction joints to maintain load transfer and reduce differential settlement.

Before explore this you lay concrete in Kansas City, you lay the system: compacted granular base, optional geotextile, correct slopes, supported steel, and a joint plan. Get those right and even a standard 4,000 PSI check this out mix will perform for decades despite KC’s tough climate.