Large flatwork handbook

Large flatwork is any continuous concrete pour over roughly 500 square feet. The threshold is not exact — it is where the working demands of the pour cross over from a small-slab job to a job that has to be planned as a placement operation. Above that size, four things change: the placement takes long enough that the mix truck rotation matters, the joint plan is tighter, the cure regime has to defend against wind and evaporation across a big surface area, and any single mistake costs more because it stretches across a bigger slab.

Examples of large flatwork the recorded holder pours across the Charlotte metro: a 600 sq ft entertainment patio, a 1,200 sq ft light-industrial pad, a 900 sq ft outdoor kitchen and dining slab, an 800 sq ft warehouse floor addition, a 1,500 sq ft equipment yard slab.

Placement on large flatwork is planned as a strip pattern, not as a free pour. The mix comes off the truck in strips against the reinforcement, and the crew works the strip before the next one lands.

• Strip layout — the slab is divided into 8-to-12-foot-wide placement strips along its long dimension. Each strip is placed continuously; the next strip is placed against the working edge of the first.
• No cold-joint — a continuous pour has no cold joint. Where a placement pause is unavoidable, an expansion joint or a bulkhead is planned into the layout so the pause happens at a designed joint, not at a random line.
• Truck rotation — trucks are ordered on a rotation so a truck is always at the site while placement is running. The mix's placement window is 60 minutes out-of-plant in normal weather and 45 in heat, and a slab that stops placement mid-pour because the next truck is late is a slab that gets a cold joint.
• Vibration — light vibration where the slab thickness or reinforcement density calls for it; over-vibration segregates the mix on a large flatwork pour more visibly than on a small slab.
• Screed and bull-float — mechanical screed (roller or vibrating screed) on any pour over 800 sq ft; bull-float in laps across the strips.

Large flatwork cracks whether the joints are planned or not. The joint plan on a big slab is tighter than on a small one — the loads on the panels are the same, the shrinkage is the same, but the sheer area means more cracks want to happen. Every crack has to have a joint waiting for it.

• Control joint spacing at the tight end of the rule — 24 times the slab thickness (8 feet on a 4-inch slab, 10 feet on a 5-inch, 12 feet on a 6-inch).
• Panel aspect 1:1 preferred on large flatwork; never over 1.5:1.
• Expansion joints at every abutment, at every fixed penetration (bollard, column, drain grate), and at 25-to-50-foot intervals across a long continuous run.
• Isolation joints around any support column or wall footing that carries load into or through the slab.
• Bulkhead-and-key at any planned pour break where the pour will resume against the earlier strip on a later day.
• Saw-cut in the 6-to-18-hour window; on large slabs the window opens earlier (6–10 hours) because the surface area sets faster than a small slab, and the cutting sequence starts at the earliest strip.

A large flatwork slab loses cure water faster than a small one — the surface area is larger, the wind exposure is larger, and there is no shading. The cure regime has to defend against that.

• Evaporative retarder during finishing on any pour above 600 sq ft in warm, dry or windy weather. Sprayed on the finished slab between passes.
• Cure kick-off before the crew leaves — curing compound sprayed on the surface, and on jobs above 800 sq ft, cure blankets pulled where wind is expected. Two-stage cure is the working default on a big exterior slab.
• Wet cure — soaker hose under burlap where the slab will be under sun and wind for the first 24 hours. Extra labor, better result.
• Cure window — seven days minimum, longer on structural work per engineer.

Finish is called against the application. Broom finish for exterior flatwork under foot or vehicle. Trowel finish for interior flatwork under coating. Stamped or exposed aggregate for decorative flatwork.

• Broom finish — cross-direction to the primary travel direction; light pass so the bristles mark the paste, not the aggregate.
• Trowel finish — mechanical trowel on any interior slab over 400 sq ft; hand trowel at edges.
• Sealer — penetrating on plain exterior; acrylic on decorative surfaces per product spec; epoxy or polyurethane on interior slabs under coating.

The sealer timeline follows the routine schedule on Curing and sealing on the installer playbook.

The service pours flatwork. It does not pour engineered structural slabs (which follow an engineer's spec), post-tensioned slabs (which are a different reinforcement method entirely), industrial floors for chemical or high-abrasion service (which take a specialty topping over the flatwork base), or floors with an integral radiant heat system (coordinated separately with the mechanical trade). Where a project needs one of those, the recorded holder discusses the scope at the site visit and refers out where the work is outside the six services on file.