ACI Decorative Flatwork cheat sheet

Stamped concrete is typically placed at a 4 in (100 mm) nominal slab thickness over a compacted base; thicker sections (5-6 in) are used where vehicle loads occur.

Stamp patterns are imprinted when the concrete has stiffened enough to hold the tool: typically after bleed water has disappeared and the surface sustains a light thumb or hand impression without mortar sticking.

Release agent (powder or liquid) is applied between the stamp and the concrete to prevent the tool from adhering; excess powder is removed after stamping before curing and sealing.

Integral color dosage is limited by the pigment manufacturer (commonly not exceeding about 10% of cement weight); overdosing weakens the mix and causes efflorescence and dusting.

Broadcast color hardener is applied in two perpendicular passes at the manufacturer's rate (commonly 60-100 lb per 1000 sq ft total) and floated in while the surface is still plastic.

A retarder (surface-set) is sprayed to keep the top mortar green so it can be exposed by washing or brushing after the bulk concrete has set, typically 12-24 hours later.

Antiquing or accent release is removed before applying the sealer; the surface must be dry (moisture vapor emission within the sealer manufacturer's limit) before sealing.

Control joints must be cut or tooled to at least 1/4 of the slab depth and spaced per ACI guidance (commonly 24-36 times slab thickness in inches) to control random cracking.

Water-cement ratio governs strength and durability: lower w/c (typically 0.40-0.45) gives higher strength and less shrinkage; decorative mixes often specify a maximum w/c rather than a slump.

Slump for stamped or hand-finished flatwork is commonly held to about 4 in (100 mm) or less; adding water on site to increase workability reduces strength approximately 200-300 psi per 0.01 increase in w/c.

Air entrainment of 5-7% is required for exterior flatwork subject to freeze-thaw; decorative toppings must use air-entrained mixes where exposed to deicing salts.

Curing compound or wet curing must begin as soon as finishing permits; ACI 308 recommends moisture retention for at least 7 days (longer for cold weather or low temperatures).

Cold-weather concreting requires the concrete temperature at placement be maintained above about 40-50 F (5-10 C) and protected from freezing until it reaches adequate strength.

Hot-weather precautions include cooling aggregates/water, placing during cooler hours, and using set retarders; plastic shrinkage cracking occurs when evaporation exceeds about 0.1 lb/sq ft/hr.

Subgrade preparation: compacted, uniform, and moistened before placement to prevent rapid moisture loss from the slab; vapor retarder under slabs on grade reduces moisture migration.

Joints: isolation joints separate flatwork from structures; contraction joints control shrinkage cracking; construction joints are planned stopping places and must be keyed or doweled as designed.