Three contractors can walk the same job site, look at the same set of plans, and hand you bids that differ by $8,000 or more. The cheapest number isn’t automatically hiding a shortcut, and the most expensive one isn’t automatically the best-built foundation. The only way to know what you’re actually paying for is to break each bid down into its parts and compare those parts against each other, not the totals against each other.
Start by matching the scope, not the price
Before you look at a single dollar figure, line up what each contractor is actually proposing to do. A bid for a 30×40 slab foundation might include excavation, gravel base, vapor barrier, rebar, forms, pour, and finishing from one contractor, and just the pour and finishing from another who assumed you’d hire an excavator separately. Those aren’t comparable numbers even though they’re both labeled “foundation bid.”
Make a simple checklist and mark what each bid covers:
- Site excavation and grading
- Gravel or compacted fill base and its depth
- Vapor barrier or moisture barrier
- Rebar size and spacing, or wire mesh
- Concrete mix strength (measured in PSI)
- Slab or footing thickness
- Forms, pouring, and finishing labor
- Cleanup and haul-away of debris and excess material
- Permits and inspection fees
If one bid is silent on any of these, call the contractor and ask directly. Don’t assume it’s included just because it seems standard. Assumptions are where change orders come from later.
Compare the actual specs, not just the labels
Two bids can both say “4-inch slab with rebar” and still describe very different foundations. A 3,000 PSI mix costs less than a 4,000 PSI mix, and the difference matters if the slab will support a garage, a shop with heavy equipment, or freeze-thaw cycles in a colder climate. Rebar spaced on 24-inch centers uses less steel than rebar on 12-inch centers, and #3 rebar (3/8 inch) is lighter and cheaper than #4 rebar (1/2 inch).
Ask each contractor to write the PSI rating, rebar size and spacing, and slab thickness directly on the bid, not just “reinforced concrete.” If a contractor won’t specify these numbers in writing, that’s worth a follow-up conversation before you sign anything. A bid that’s $2,000 cheaper because it uses 3,000 PSI mix instead of 4,000 PSI and skips the vapor barrier isn’t a better deal, it’s a different product.
Ask how each contractor prices materials and labor
Concrete pricing moves with the market, and a bid that was accurate in March can be off by 10-15% by June if it doesn’t account for material cost swings. Ask each contractor whether their bid is a fixed price or subject to adjustment if concrete, steel, or lumber prices change before the pour date. A fixed bid protects you from surprises but sometimes carries a built-in cushion. A bid with an escalation clause might start lower but expose you to increases later.
Also ask how labor is structured. Some contractors carry their own concrete finishing crew, and others subcontract that work out. A sub-contracted crew isn’t automatically worse, but it adds a layer of coordination and sometimes a markup you can’t see in the line-item price. Knowing who is physically doing the work, and whether that crew is employed directly or brought in for the job, tells you something about accountability if a problem shows up in the finished slab.
Check the timeline and what happens if weather delays the pour
A bid that looks $3,000 cheaper can still cost you money if it stretches your project timeline by three weeks. Ask each contractor for a specific start date and pour date, not just “we’ll get to it soon.” Concrete work is weather-dependent, and a contractor with three other jobs stacked ahead of yours may not be able to pour until conditions are right, which pushes your framing crew, your inspection schedule, and every trade behind them.
Ask directly what happens if rain or freezing temperatures delay the pour. A contractor with a clear plan for covering and protecting a site, or rescheduling without penalty, is telling you something about how they manage a job when conditions aren’t ideal. A vague answer here often predicts a vague answer to other problems later.
Look for what’s missing, not just what’s listed
The bids that cause the most trouble later are rarely the ones that look obviously wrong. They’re the ones that leave things out. Watch for these gaps:
- No mention of permit responsibility (who pulls it and who pays the fee)
- No warranty language on cracking, settling, or workmanship
- No allowance for soil testing or engineering review on tricky sites
- Vague payment terms, like “50% up front” with no schedule for the rest
- No named point of contact for questions during the job
A missing warranty clause is a real cost even though it doesn’t show up as a number on the page. If a slab cracks beyond normal shrinkage cracking eight months after the pour, you want to know in writing whether that’s covered and for how long, typically one to five years depending on the contractor and the region.
Once you’ve matched scope, specs, material terms, timeline, and warranty coverage across all your bids, write the three or four differences that actually explain the price gap on a single sheet of paper. Bring that sheet to the contractor you’re leaning toward and ask them to confirm each point in writing before you sign the contract.
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