How to Compare Concrete Bids: The Scope Items Most GCs Miss

Concrete looks like a commodity. It comes in yards, it costs a price per yard, and three contractors quoting the same slab should be in the same ballpark. Except they're almost never in the same ballpark — and the differences that explain the variance are almost never visible in the summary price.

On a typical commercial concrete scope — parking structure, slab on grade, or foundation system — the spread between the low and high bid commonly reaches 25-40%. That spread isn't random. It comes from specific differences in mix design, reinforcement specifications, finishing standards, and which contractor actually read the geotechnical report.

Here's what to check when you're comparing concrete bids — and the scope items that turn the low bid into the expensive bid.

Why Concrete Bids Are Hard to Compare

Concrete bids are difficult to compare because the cost is distributed across materials, labor, and equipment in proportions that vary significantly by project type and contractor approach. Mix design alone — the specific concrete formulation — can account for $8-15 per cubic yard difference in material cost on a single pour.

Reinforcement is where the largest scope gaps hide. Some contractors bid 'rebar per plan' — meaning they priced what's shown on the drawings, no more. Others read the structural notes more carefully and priced the additional tie beams, grade beams, or thickened edges called out in specifications but not shown prominently on plans. You won't know which approach each contractor took until you ask.

Site conditions are another source of variance. A contractor who reviewed the geotech report knows the soil is expansive and has priced moisture barrier, compaction, and underslab prep accordingly. A contractor who didn't read the report quoted a standard slab package and will come back with change orders when they start digging.

Mix Design and Concrete Specifications

Not all concrete is created equal, and not all contractors price the same mix. Standard compressive strength for residential slabs is 3,000 psi. Commercial slabs often require 4,000 psi or higher. High-traffic areas may require air-entrainment, fiber reinforcement, or fly ash additives. Each specification affects cost.

Reinforcement Scope

Reinforcement is the most common source of concrete bid variance. What's priced by one contractor as "rebar per structural drawings" may mean different things depending on which drawings they referenced, how they read the bar schedule, and whether they included all the steel shown in the details.

Rebar vs. Wire Mesh vs. Fiber

Traditional rebar reinforcement is more expensive than welded wire mesh or fiber reinforcement, but the structural performance differs. Some contractors will substitute where they think they can get away with it. Confirm each bid specifies the exact reinforcement type, size, and spacing called for in the structural drawings.

Grade Beams and Thickened Edges

Grade beams and thickened slab edges are often shown in structural details but not highlighted on the plan sheets. Contractors who read the full drawing set price them; contractors who read only the plans may miss them entirely. On a commercial foundation, omitted grade beams can represent $15,000-30,000 in missing scope.

Finishing Standards and Surface Preparation

Concrete finishing cost varies enormously based on the final surface requirements. A basic broom finish for a utility slab costs roughly $0.50-0.75 per square foot in labor. A steel-trowel finish for a warehouse floor costs $1.50-2.50. A super-flat floor with a specified F-number tolerance can reach $4-6 per square foot.

Some contractors will bid broom finish when the specs call for steel trowel, because broom finish is what they default to when specs aren't explicit. Confirm finishing specifications are called out clearly in your RFB and that each contractor has priced the correct finish type.

• Finish type: broom, steel trowel, or super-flat (specify F-number)
• Curing method and duration (wet cure, curing compound, blankets)
• Joint sawcutting timing and depth requirements
• Sealers or coatings included vs. excluded
• Protection during cure period (in cold or hot weather)

Site Preparation and Subgrade Work

Concrete bids often diverge most on site prep — the work that happens before any concrete is placed. Compaction requirements, moisture barrier specifications, gravel base depth, and import material requirements are all line items that some contractors include and others don't.

Before comparing concrete bids, confirm which contractors have received and reviewed the geotechnical report. The ones who haven't aren't pricing the same project. Comparing bids on equal terms requires that every contractor is working from the same information.