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Top Mistakes Contractors Make Before Core Drilling

Core drilling is straightforward until you hit something you didn't expect. Rebar bends the bit. A post-tension cable strike releases tension energy into the surrounding slab. Cutting a conduit kills power or floods the floor. Most of these incidents are preventable — the core was drilled without a GPR scan first. Here are the most common mistakes that cause damage.

1. Skipping the Scan on Post-Tensioned Slabs

Florida has a large amount of post-tensioned construction. Many contractors assume a slab is conventionally reinforced when it's actually PT — and the scan gets skipped. Signs a slab may be PT: stressing pockets or end caps visible at slab edges, plastic or metal end covers at the perimeter, or a building built after the mid-1980s in a multistory commercial or residential format. When in doubt, scan first.

2. Scanning Only the Drill Point, Not the Work Zone

A scan that covers only the exact 2-inch circle of the planned core can miss a PT tendon running diagonally nearby or a conduit curving through the area. Scan a grid around the drill point — typically 18 to 24 inches in each direction — so the full work zone is assessed before the rig is positioned. This also gives you room to shift the core location if a conflict is found.

3. Not Briefing the Drill Operator on the Markings

The scan gets done. Marks are on the slab. The technician leaves. The drill operator arrives, doesn't understand the markings, and drills at the wrong point. Scan markings are only useful if they are communicated directly to the crew doing the work. A walk-through with the foreman or drill operator before the rig moves is not optional — it's part of the process.

4. Relying on Old Drawings as Ground Truth

As-built drawings from 30 years ago show what was designed, not what was built or changed later. Renovation work often encounters conduit that was rerouted, added, or capped without documentation. Use drawings to inform the scan scope — not to replace it.

5. Skipping the Scan on "Quick" Jobs

Single-point cores — a drain, a pipe sleeve, a vent — where scanning feels like overkill. These are often where strikes happen, precisely because the pre-task discipline is skipped. The scan is fast and the cost is a fraction of the repair. The process is the same regardless of job size.

6. Not Adjusting the Location When a Conflict Is Found

The scan identifies a conflict and the foreman decides to drill anyway because the schedule is tight. When a conflict is found, the first question should be: can we shift the core location to avoid it? In most cases, a few inches of adjustment resolves the conflict. This flexibility is only available when the scan is done before the rig is positioned.

Related services: Core Drilling Scan | Post-Tension Cable Scanning | Rebar Scanning | GPR Concrete Scanning