A concrete slab is one of the most versatile and durable surfaces you can build. Garage floors, workshop pads, equipment pads, covered patios, barn floors — they all start with the same fundamentals: a solid base, the right mix, accurate volume, and proper finishing. Here's how to get it right from start to finish.

Base Preparation: The Most Important Step

Concrete doesn't float — it follows the shape of what's underneath it. A poorly prepared base leads to cracking, settling, and water infiltration. Before you order concrete, your base needs to be right.

Remove all organic material (topsoil, roots, vegetation) — organic material compresses and causes settling
Compact the subgrade with a plate compactor or roller
Add 4–6 inches of compacted gravel base (crusher run or #57 stone)
Grade the base to your finished slab elevation, accounting for slope for drainage
Install a vapor barrier (6-mil poly) for interior slabs to prevent moisture migration

Choosing the Right PSI and Mix

For most residential slabs, 3,000–3,500 PSI is the right range. Garage floors that will see vehicle traffic, oil, and deicing salts benefit from 4,000 PSI and a low water-to-cement ratio for better surface durability.

3,000 PSI — patios, walkways, light-use pads
3,500 PSI — garage floors, standard residential
4,000 PSI — heavy-use garage floors, shop floors, equipment pads

Consider adding synthetic fiber to the mix for crack control, especially on larger slabs. It's a low-cost add-on that reduces plastic shrinkage cracking during the cure.

Calculating Your Volume — and Why to Order Extra

Measure length × width × depth (in feet), divide by 27 for cubic yards. A 24 ft × 24 ft garage slab at 4 inches thick: 24 × 24 × 0.33 ÷ 27 = 7.1 cubic yards.

Always add 5–10% overage. Your base is never perfectly level — low spots and edges consume more concrete than your calculation assumes. On a 7-yard pour, order 7.5–8 yards. Running short means stopping mid-pour, which creates a cold joint — a visible, structural weak point in your slab.

Reinforcement

Wire mesh (6×6 W1.4/W1.4 welded wire fabric) is the standard for residential slabs. Place it on chairs or dobies so it sits in the middle third of the slab depth — not on the ground where it does nothing. For heavier loads, use #3 or #4 rebar on an 18-inch grid.

Control Joints

Concrete shrinks as it cures. Control joints — tooled or saw-cut grooves — give it a place to crack in a straight line rather than randomly. Space them no more than 2–3 times the slab thickness in feet (so every 8–10 feet for a 4-inch slab). Cut saw joints within 4–12 hours of finishing.

Finishing the Slab

Screed: strike off the surface to the correct elevation with a screed board
Bull float: smooth the surface and embed aggregate
Wait for bleed water to evaporate before finishing — working wet concrete weakens the surface
Hand float or power trowel for a smooth finish; broom finish for exterior traction
Apply curing compound immediately after finishing, or keep moist for 7 days

Timing Your Pour

In Charlotte's summer heat, schedule pours for early morning. High temperatures accelerate set time, leaving less time to place and finish. Ask about retarder admixtures for afternoon pours or large slabs. In cooler months, accelerators can help you hit your finishing window.

UNO Concrete delivers slab mixes across the Charlotte metro — residential, commercial, and everything in between. Call us with your dimensions and we'll help you calculate the right volume, choose the right mix, and schedule delivery when you're ready.

Pouring a Concrete Slab: Everything from Base Prep to Finishing