When you need a hole through a concrete wall, floor, or foundation, coring is faster and cleaner than busting through with a jackhammer. The challenge is specifying the right depth and diameter so the job gets done correctly the first time—and so you don't overpay for unnecessary work.
Why Depth and Diameter Matter
Concrete coring isn't one-size-fits-all. A 2-inch hole for electrical conduit requires different equipment and pricing than an 8-inch core for HVAC ducting. Depth matters equally: a 6-inch core through a standard slab costs far less than drilling 24 inches through a thick foundation or multi-layered assembly. Contractors who spec the wrong dimensions risk callbacks, material waste, and schedule delays.
Common Coring Sizes and Applications
Most residential and light commercial work falls into predictable ranges:
- 1–2 inches: Plumbing, electrical, small mechanical runs
- 3–4 inches: HVAC returns, larger electrical panels, drainage
- 6–8 inches: Structural penetrations, major ductwork, utility feeds
- 10+ inches: Stair openings, large equipment access, structural modifications
Depths vary by application. A typical concrete slab core might be 4–6 inches deep. Foundation or wall penetrations often run 8–16 inches, depending on wall thickness. Structural renovations requiring access through multiple stories can demand 20+ inches.
What Contractors Actually Charge
Pricing depends on three factors: hole size, depth, and concrete density.
A single 4-inch-diameter, 4-inch-deep core in standard concrete typically runs $60–$150. Scaling up to an 8-inch diameter and 12-inch depth jumps to $200–$400 per hole. Multiple cores in one job usually get a per-hole discount; a contractor quoting five 6-inch cores might charge $100–$120 each instead of $130–$150.
Reinforced concrete (rebar or post-tension cables) adds complexity and cost. Some contractors charge 30–50% more when rebar is present because the drill bit encounters metal and drilling slows significantly. If the core hits a major post-tension cable, the job stops and you're calling a structural engineer—factor that risk into your timeline.
Dense concrete, granite aggregate, or aged concrete all slow drilling. A vintage 1960s foundation might cost more to core than a 10-year-old slab, even at the same size.
Steps to Specify a Coring Job
1. Identify what needs to pass through. HVAC ducts, copper lines, electrical conduit? Know the outside diameter plus any fitting or insulation thickness. Add 0.5–1 inch to account for installation tolerance.
2. Locate rebar and embedded utilities. Before calling a coring contractor, request a concrete scan with ground-penetrating radar (GPR). Scanning costs $300–$600 but prevents hitting rebar or post-tension cables. Many contractors include a basic scan in their estimate; ask.
3. Determine depth and thickness. Measure the concrete thickness at your penetration point. If you're unsure, contractors can confirm during the site visit.
4. Get multiple quotes. A single phone call with dimensions usually gets you a ballpark price. Honest contractors will ask about rebar, concrete age, and structural implications before quoting. Get at least two estimates; pricing can vary 20–40% between shops.
5. Confirm cleanup and edge quality. Will the contractor remove slurry and dust? Do you need a clean edge or just a functional hole? These details affect labor cost and timeline.
Signs of a Reputable Coring Contractor
- Asks about embedded utilities and rebar before quoting
- Includes or recommends a GPR scan
- Provides equipment that matches the job (rotary core drills for standard work, wet drilling to control dust)
- Clarifies whether diamond blade segmentation is appropriate for your concrete type
- Offers same-day or next-day scheduling for straightforward work
- Provides written estimates with scope (diameter, depth, number of cores)
If a contractor quotes without asking questions, consider that a warning sign.
Tools for Finding the Right Contractor
Getting honest, competitive bids is easier than ever. Platforms like Mercoly let you compare concrete coring contractors side-by-side, see customer reviews, and request quotes for your specific hole size and depth—no guesswork.
Frequently Asked Questions
Q: Does my 4-inch core need to be exactly 4 inches, or is there tolerance? A: Contractors typically drill within ±1/8 inch of your specified diameter; anything tighter requires a specialty drill bit and costs more. For mechanical installs, ±1/4 inch is acceptable and standard.
Q: How long does a typical coring job take? A: A single 6-inch core takes 15–30 minutes depending on concrete hardness. Multiple cores and rebar encounters add 10–20 minutes per hole; budget a full day for any job involving inspection, scanning, or 5+ holes.
Q: Can I do concrete coring myself? A: Wet coring requires a rental diamond-core drill ($40–$100/day), water supply, and dust control setup. It's feasible for one or two holes in soft concrete, but equipment cost and noise issues usually make hiring a pro the smarter choice.
Find a trusted concrete coring contractor in your area and get accurate quotes today.