A bad foundation interview can cost you tens of thousands in rework or structural problems down the line. Asking the right questions upfront separates contractors who cut corners from those who deliver solid, code-compliant work. Here's how to interview concrete foundation contractors and actually know what you're getting.
Request References Tied to Your Soil Type
Don't just ask for three random job sites. Ask for references where the contractor worked in your soil composition—clay, sandy loam, or bedrock. Soil conditions directly affect foundation depth, footing width, and drainage requirements. A contractor who's built 50 houses on sandy soil might be inexperienced with clay-heavy ground that demands different compaction and moisture management. Call those references and specifically ask whether the foundation has shown any settling, cracking, or water intrusion since completion.
Confirm Their Licensed Status and Insurance
Verify the contractor holds a current general contractor or concrete license in your state (requirements vary by location). Request proof of liability insurance ($1–2 million is standard) and workers' compensation. Ask your local building department directly whether the contractor has open complaints or past violations. This takes 10 minutes and eliminates fly-by-night operators who vanish when problems surface.
Understand Their Soil Testing Protocol
Ask what soil testing they perform before breaking ground. Legitimate contractors typically order a soil boring or professional geotechnical report, which costs $800–$2,000 but reveals bearing capacity and frost depth—critical numbers for footing design. If a contractor says "we don't need soil testing; we just go by what worked on the last job," that's a red flag. Frost depth alone varies by region (4 feet in Minnesota, 2 feet in North Carolina), and footings placed too shallow heave and crack in freeze-thaw cycles.
Ask About Their Moisture Barrier Strategy
Concrete wicks moisture like a sponge. A quality foundation needs vapor barriers, drainage planes, and perimeter drainage systems. Specifically ask:
- Do they install a polyethylene or engineered moisture barrier under the slab?
- What's their approach to perimeter drainage (interior French drain, exterior swale, or sump pump)?
- Do they recommend or install a radon mitigation vent during the concrete pour (easier and cheaper then than retrofitting later)?
- How do they handle the footing-to-wall transition to prevent water entry?
Vague answers here suggest the contractor treats foundation work as pouring concrete, not creating a durable, dry assembly.
Get a Detailed Written Estimate
The estimate should itemize:
- Excavation and backfill
- Soil compaction and testing (if applicable)
- Footing size and depth (e.g., "24-inch-wide footings, 48 inches deep")
- Concrete mix design (strength in PSI—3,000 PSI is typical for residential)
- Reinforcement (rebar grade, spacing, placement depth)
- Moisture barriers and drainage details
- Frost protection if required
- Timeline and cleanup
Pricing for a typical residential foundation (2,000 sq ft slab or 1,200 linear feet of footings) ranges $6,000–$15,000 depending on region and complexity. A line-item estimate prevents surprises and shows the contractor understands the scope.
Talk Timeline and Weather Protocols
Foundation work stops in freezing temperatures—concrete won't cure properly below 50°F. Ask how they schedule around weather and whether they plan winter protection (heated enclosures, curing blankets). Also confirm they won't pour over frozen subgrade, which compromises bearing. A realistic timeline for a typical house foundation is 2–4 weeks from excavation to cured concrete ready for framing.
Verify Code Compliance Plans
Ask specifically how they ensure compliance with your local building code. Do they pull permits? Will they coordinate inspections at footing placement and before backfill? Building inspectors verify that footings reach frost depth, that soil is properly compacted, and that rebar is positioned correctly. Contractors who resist inspections or skip permits are gambling with your structure.
Compare and Verify With Mercoly
Gathering and comparing multiple contractor responses is easier with platforms like Mercoly, where you can review and compare vetted concrete foundation providers in one place, read real feedback, and ensure you're getting consistent, code-aligned recommendations.
Frequently Asked Questions
Q: How deep should my footings be? Footing depth depends on frost line depth in your region and soil bearing capacity—your contractor should confirm both before quoting. In most areas, code requires footings to extend below the frost line to prevent heave from freeze-thaw cycles.
Q: What's the difference between a monolithic slab and a stem-wall foundation? A monolithic slab pours footings and slab in one pour (faster, cheaper, used for mild climates); a stem-wall separates the footing and foundation wall, offering better moisture control and is required in cold regions with deep frost lines.
Q: Can I use my contractor's estimate to get a second opinion from another contractor? Absolutely—share the estimate details (not just the price) with other contractors so they're bidding the same scope, preventing apples-to-oranges comparisons.
Interview at least three contractors, ask these questions, and you'll hire someone who builds foundations that last 50+ years, not patches that fail in five.