Slabs hide rebar, conduit and post-tension cables. Scanning before coring or saw cutting protects the crew, the structure and the schedule.
In this article
What hides in the slab
Rebar, post-tension tendons, electrical conduit, plumbing and radiant heat tubing. Old drawings rarely show everything.
How scanning works
A trained technician uses ground penetrating radar to locate objects and marks them on the surface.
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Mark the layout first
Mark every planned core and cut before the scan, so the technician checks exactly those spots and nearby areas.
Post-tension slabs
Cutting a tendon is dangerous and expensive. Treat any post-tension slab as high risk and involve the engineer of record.
Schedule it
Book the scan a few days before coring, after layout is final. A changed location means a new scan.
Who pays
Decide in the subcontract whether scanning belongs to the trade that cores or to the general contractor.
Keep the record
Photos of the marks and the scan report go in the daily log. They matter if something is hit later.
Common mistakes
Coring without a scan, moving the hole after the scan and trusting old as-builts.
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Frequently asked questions
Is GPR scanning always accurate?
Ground penetrating radar is very useful, but results depend on the slab, the equipment and the technician. Treat the scan as one layer of protection and follow the structural engineer's guidance, especially on post-tension slabs.