A 20×20 slab (400 sq ft) is a common size for patios and sheds. In Kansas City, total price depends on base prep, thickness, reinforcement, access, and finish. Instead of chasing a single number, use this guide to understand the scope items that drive cost and long-term performance.
Key Cost Drivers
- Base preparation: 4–6" of compacted 3/4" minus crushed stone (DGA), proof-rolled subgrade, and geotextile if soils are soft/clayey. Slab thickness: 4" for patios/sheds; 5–6" if you expect heavier loads or want extra durability. Reinforcement: Rebar grid on chairs (common) or welded wire; dowels at thresholds/adjacent slabs. Jointing: Spacing ≈ 24–36× slab thickness (in inches) with early-entry sawcuts to prevent random cracking. Finish & curing: Broom or decorative stamp; curing compound applied immediately after finishing/jointing. Access/weather: Backyard wheelbarrow runs, pumping needs, or hot/cold weather admixtures and blankets.
What a Typical Scope Looks Like
For a patio-style 20×20 in KC neighborhoods: remove sod, excavate to subgrade, place/compact 4–6" DGA base, set forms/elevations, install rebar on chairs, order air-entrained ready-mix (3,500–4,000 PSI), place and finish with light broom, cut joints same day, cure immediately, and backfill edges after strip.
Tips to Keep Costs Predictable
- Specify the system in writing: Base material/thickness, slab thickness, rebar size/spacing, joint plan, finish, and curing method. Plan drainage: Positive slope away from structures and downspout extensions so edges don’t saturate and spall in winter. Choose a practical finish: A clean broom texture offers great traction and value; stamping adds labor and materials.
Local Considerations
Expansive clay and freeze–thaw cycles in Kansas City magnify the value of dense base, tight joints, and proper curing. take a look Skipping these to “save” often leads to edge chipping and early cracking—costs you’ll pay later.
Takeaway
Price depends on scope. Ask your contractor for a detailed, apples-to-apples proposal that spells out base prep, thickness, rebar, jointing, finish, and curing. That’s how you get a durable 20×20 slab that performs for years in Kansas City’s climate.
Authority Reference
For slab and jointing best practices, see the American Concrete Institute.