Last updated: October 2026
Quick answer
A commercial concrete slab is typically 4 to 6+ inches thick depending on loads, poured on a compacted granular base, reinforced with rebar, wire or fiber, and cut with control joints spaced roughly 2 to 3 times the slab thickness (in feet). Interior slabs that get flooring or coatings usually need a vapor retarder. Final specs come from the project's plans or engineer. Happy Valley Concrete pours commercial slabs, pads and flatwork in Happy Valley and the Portland area; call (503) 782-6069.
What makes a commercial slab different
A residential patio and a warehouse floor are both "concrete slabs," but they are built for very different jobs. Commercial concrete slabs carry forklifts, delivery trucks, pallet racking, equipment and heavy foot traffic, often for decades. They also tend to be inspected, follow plans or engineering, and have tighter tolerances for flatness, drainage and joint layout. This guide covers the basics owners and builders ask about before a commercial pour in the Portland area.
Thickness
- 4 inches: sidewalks, light-duty pads, small office or retail floors with foot traffic only.
- 5 to 6 inches: shop floors, parking pads and aprons, light vehicle traffic, light racking.
- 6 inches and up: forklift traffic, trucks, dumpster pads, heavy racking and equipment. These should be designed for the actual loads.
Thickness matters more than almost anything else for load capacity; an extra inch adds a lot of strength. Thickened edges and footings under racking or columns are common.
Base and subgrade
Many slab failures start below the concrete. Soft spots, organic soil, poor compaction and water under the slab cause settling and cracking. A proper commercial slab sits on a compacted subgrade and a compacted crushed-rock base, with drainage handled so water does not sit underneath. In the Portland area's wet winters and clay soils, base preparation is critical; see our wet-climate concrete guide.
Concrete mix and strength
Commercial flatwork is commonly specified around 3,500 to 4,500 PSI, with air entrainment for exterior concrete exposed to freezing. Lower water content makes stronger, more durable concrete. Plans, engineers or the general contractor usually set the mix; we follow the spec and keep delivery tickets.
Reinforcement
Rebar, welded wire mesh and fiber reinforcement each have a place. Reinforcement does not stop concrete from cracking; it holds cracks tight and adds load capacity. Dowels at construction joints help transfer loads between pours so slab edges do not curl or break under forklifts.
Control joints and layout
Concrete shrinks as it cures, and it will crack somewhere. Control joints decide where. A common rule is joint spacing in feet of about two to three times the thickness in inches, laid out in squares rather than long thin panels. Joints are saw-cut soon after finishing. For floors that will see forklifts, joint filler choice matters too.
Vapor retarders for interior slabs
If the slab will get flooring, coatings or moisture-sensitive storage, a vapor retarder under the slab reduces ground moisture coming through. Without it, epoxy coatings and flooring adhesives can fail years later.
Finish, curing and protection
Interior slabs are usually steel-troweled smooth; exterior slabs get a broom finish for traction. Proper curing keeps the surface strong and reduces dusting and cracking. Traffic should be kept off until the concrete has gained enough strength for the loads.
Commercial concrete in Happy Valley and Portland
Happy Valley Concrete pours commercial slabs, shop and warehouse floors, pads, aprons and sidewalks across Happy Valley, Clackamas, Portland, Gresham and nearby towns. See our commercial concrete service page, the project process and cost guide (national published ranges, not our prices).
Frequently Asked Questions
How thick should a commercial concrete slab be?
It depends on the loads. Light commercial floors and sidewalks are often 4 to 5 inches; slabs for forklifts, trucks or racking are commonly 6 inches or more and are designed by an engineer for the specific loads and soil.
What PSI concrete is used for commercial slabs?
Commercial flatwork is commonly specified somewhere around 3,500 to 4,500 PSI, and exterior concrete in freeze-thaw areas is usually air-entrained. The project's engineer or plans set the actual mix.
Do commercial slabs need rebar?
Most do. Rebar, welded wire or fiber reinforcement is chosen based on loads, slab thickness and the engineer's design. Reinforcement controls crack width; joints control where cracks form.
How far apart should control joints be in a commercial slab?
A common rule of thumb is joint spacing in feet of no more than about two to three times the slab thickness in inches, so roughly 10 to 15 feet for a 5- to 6-inch slab. Plans and engineers set the final layout.
Do interior commercial slabs need a vapor barrier?
Slabs that will receive flooring, coatings or moisture-sensitive storage usually get a vapor retarder under the slab. It reduces moisture moving up from the ground, which can ruin adhesives and coatings.
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