Concrete Scope of Work: What GCs Need to Include When Buying Out a Concrete Sub

Concrete is one of the most unforgiving trades on any project — once it's poured and cured, deficiencies are expensive to correct and sometimes impossible to fix without demolition. A complete concrete scope of work defines not just what gets poured, but the mix design, the formwork requirements, the embedded items, the testing protocol, and the finishing standard — before the first truck shows up. This guide covers what to include in a concrete scope of work, organized by the trade-specific requirements, package items, and the coordination with adjacent trades that determines whether the pour goes as planned.

Mix Design and Materials

Tip: "Ready-mix concrete per structural drawings" is not a scope. Every element of the concrete mix design that matters for structural performance, durability, and constructability must be specified. The structural engineer's specifications govern — your scope confirms they're in the sub's price.

• Specified compressive strength (f'c): Specify compressive strength requirement for each element type — slab on grade, suspended slab, columns, walls, footings. Strengths are not interchangeable. Specify the test age (28-day is standard; 56-day may be specified for high-strength elements).
• Exposure class and durability: Specify concrete exposure class per CSA A23.1 or ACI 318 — this drives maximum water-cement ratio, minimum cement content, and air entrainment requirements. Concrete placed in parking structures, exterior slabs, or in contact with sulphate soils has different durability requirements than interior concrete. Specifying only f'c without exposure class results in mixes that meet strength but fail durability.
• Aggregate size and type: Specify maximum aggregate size (typically 20mm or 25mm for structural concrete; 10mm for concrete pumped through small-diameter lines). Aggregate type affects workability, finish, and durability in aggressive environments.
• Admixtures: Specify acceptable admixture types — water reducers, superplasticizers, air-entraining agents, accelerators, retarders. Confirm air entrainment requirements for all exterior concrete (minimum 4–7% air by volume for freeze-thaw exposure). Calcium chloride admixtures are prohibited in reinforced concrete — specify this explicitly.
• Supplementary cementitious materials (SCMs): Fly ash, slag, and silica fume substitutions for Portland cement — specify acceptable substitution percentages per CSA or ACI requirements. SCMs affect early-age strength gain and finishing behavior — the sub must account for this in the construction schedule.

Formwork

• Formwork design: Specify that formwork is designed and constructed to support all loads — concrete pressure, construction live loads, equipment loads, and impact — without excessive deflection. Require formwork drawings signed and sealed by a P.Eng. for formed suspended slabs, walls over 3m high, and any shored or re-shored assembly.
• Form release agents: Specify acceptable form release agent types — petroleum-based agents contaminate surfaces receiving bonded waterproofing, epoxy coatings, or architectural concrete finishes. Specify a reactive or vegetable-oil-based release agent for all elements receiving coatings or architectural finishes.
• Form removal (strip) timing: Specify minimum concrete age or strength requirement before formwork removal. Side forms on vertical elements — typically 12–24 hours at ≥3.5 MPa. Shores and re-shores under suspended slabs — must meet structural engineer's requirements and are not to be removed until slab has reached a defined percentage of f'c (typically 75%). Premature shoring removal causes slab cracking and deflection.
• Architectural concrete: Where concrete is to remain permanently exposed, specify form liner type, tie hole treatment, bug hole repair limits, form alignment tolerances (typically 3mm over 3m), and acceptable color consistency. These requirements must be in the scope before any formwork is built — not discovered at punchlist.

Reinforcement

• Reinforcement supply: Confirm whether rebar supply and installation is in the concrete sub's scope, or whether it's a separate rebar subcontract. If separate, confirm the interface — who provides placing drawings, who installs chairs and supports, and who calls the rebar inspection.
• Cover requirements: Specify minimum concrete cover for all element types — this is set by the structural drawings and exposure class. Rebar chairs that provide correct cover are the concrete sub's responsibility. Insufficient cover in slabs on grade or parking structures is the most common cause of premature reinforcement corrosion.
• Lap splices and development length: Specify that lap splices and development lengths must comply with the structural drawings. Field modifications to lap locations require structural engineer approval — this must be in the concrete sub's scope obligations.

Placement and Consolidation

• Pump vs. direct chute: Specify acceptable placement method for each element. Concrete pumped through small lines must have a mix design appropriate for pumpability — this affects aggregate size and slump requirements. Confirm pump location and line routing do not damage adjacent work.
• Slump and workability at point of placement: Specify maximum slump at the point of placement (not at the truck). Adding water to concrete at the site to increase workability reduces strength and durability — specify that no water addition is permitted at the site without written authorization from the engineer.
• Consolidation (vibration): Specify internal vibrator type, minimum vibrator head diameter, and insertion spacing and depth. Inadequate vibration produces honeycombing — a structural deficiency in columns and walls that is expensive to repair and may require element replacement.
• Cold and hot weather placement: Specify concrete temperature limits at placement — minimum 10°C for cold weather, maximum 35°C for hot weather. Cold weather protection requirements (insulated formwork, heated enclosures, extended curing) must be in scope for any pour scheduled between October and April in northern climates.

Finishing and Curing

• Floor slab finishing: Specify floor flatness (FF) and floor levelness (FL) requirements per ASTM E1155 for each area of the project. Warehouse floors receiving fork truck traffic require FF35/FL25 minimum. Office floors under raised access flooring require FF50/FL30. Specify the floor flatness measurement protocol and who performs it.
• Surface treatment: Specify surface treatment for exposed concrete floors — hard trowel only, dry shake hardener, penetrating densifier, or topical sealer. The choice affects surface hardness, dust generation, stain resistance, and chemical resistance. Specify by area on the finish schedule.
• Curing method and duration: Specify curing method (wet curing, curing compound, polyethylene sheeting) and minimum duration by element type. Minimum 7 days moist curing for structural concrete; minimum 10 days for concrete in aggressive exposure conditions. Curing compound must be compatible with any subsequent floor coating or surface treatment — many curing compounds prevent bonding of epoxy coatings.
• Joint layout: Specify control joint spacing and sawcut timing for slabs on grade. Sawcut joints must be cut within 4–12 hours of finishing (before random cracking initiates). Provide a joint layout drawing approved by the structural engineer — do not allow the concrete sub to lay out joints in the field without a drawing.

• Testing and inspection: Specify the concrete testing program — cylinder samples (minimum 3 per 50m³ or per truck load on critical pours), slump tests at the truck and at point of placement, air content tests, and concrete temperature tests. Confirm who pays for testing — typically the GC carries testing costs as a direct cost, but this must be stated explicitly. Failed cylinder results must trigger a defined response protocol.
• Embedded items coordination: The concrete sub must coordinate all embedded items — MEP sleeves, anchor bolts, embed plates, conduit, drain bodies — before any pour. Require the sub to produce a pre-pour checklist signed by the GC confirming all required embedded items are in place. This single requirement eliminates the majority of core drilling after pours.
• Pumping costs: Concrete pump mobilization, setup, and operation is a significant cost on high-rise and podium projects. Confirm whether pump costs are in the concrete sub's scope or carried as a separate GC cost. Pump location and access must be confirmed before the pour — pump booms cannot be located on structural slabs without engineering review.
• Winter and summer protection: Cold weather heating, insulated blankets, and extended monitoring are costs that vary significantly with weather conditions. Specify the concrete sub's responsibility for weather protection and confirm whether the GC carries the cost of extreme weather events or whether it's included in the sub's lump sum price.
• Surface repairs: Specify the acceptable repair method for honeycombing, cold joints, and bug holes — typically SIKA, Emaco, or equivalent structural repair mortar applied per the manufacturer's system. Cosmetic patching of structural honeycombing is not acceptable — require a repair method approved by the structural engineer.
• Shoring and re-shoring schedule: For multi-level concrete structures, specify the shoring and re-shoring configuration required to distribute loads from upper pours to lower slabs. The structural engineer must design the shoring layout — confirm it's in the structural package and the concrete sub's scope to execute it.

• Structural engineer: Require the concrete sub to submit a pre-pour inspection request 48 hours before any structural pour. The structural engineer of record (or their designated inspector) must sign off on reinforcement placement, embedded items, and formwork before concrete is placed. No pour should proceed without this sign-off.
• MEP trades: All MEP sleeves, conduit, and drain bodies must be confirmed installed and inspected before the pour. Require a signed pre-pour checklist. The consequences of a missed sleeve — core drilling through post-tensioned slabs — can be structural as well as costly. Best practice: hold a pre-pour meeting for every major slab pour with all trades who have embedded items.
• Rebar sub (if separate): Confirm the rebar sub has completed placement, inspection, and tie-off before the concrete sub begins formwork closure and pour preparation. Define the interface at the pre-pour inspection — the concrete sub cannot pour until the rebar sub's work is inspected and accepted.
• Waterproofing: Below-grade concrete elements receiving waterproofing treatment must be inspected before waterproofing is applied. Confirm that the concrete surface quality meets the waterproofing manufacturer's requirements. Cold joints, honeycombing, and surface contamination are incompatible with most bonded waterproofing systems — identify and repair before waterproofing proceeds.
• Surveying: Slab elevation survey before and after pour is required for slabs with flatness requirements. The survey establishes the pre-pour substrate condition and confirms the poured slab meets specified tolerances. Specify who provides the survey — typically the GC or the concrete sub on projects with strict flatness requirements.
• Masonry and cladding: Anchor bolt locations cast into concrete for masonry and cladding attachment must be confirmed against the masonry/cladding shop drawings before the pour. Mislocated anchor bolts in concrete are expensive to relocate — they cannot simply be moved after the pour.