Core cutting looks simple: set up the rig, drill a round hole, pull the core out. That’s why it’s often handed to whoever is free on site.
But most slab damage from coring doesn’t come from the drill. It comes from small decisions made before and after the hole. Here are six mistakes we see on sites across Dubai and Abu Dhabi, what each one does to the slab, and how to avoid them.
Mistake 1: Drilling without scanning first
What happens: The bit goes straight through rebar, a post-tension cable or a live conduit hidden in the slab.
Why it damages the slab: Cutting main reinforcement reduces the slab’s strength at that point. Cutting a PT tendon is far worse. The stored tension releases, the slab loses part of its support, and you’re looking at a major structural repair.
Do this instead: Scan every core location with GPR concrete scanning before drilling. Move the core a few centimetres if needed to land in a clear zone.
Mistake 2: Putting cores too close together or too close to edges
What happens: Cores are lined up tightly for a pipe run, or drilled right next to a slab edge, opening or column.
Why it damages the slab: Each hole removes concrete and interrupts the paths that loads travel through. A tight cluster acts like one large opening, and a core near an edge can crack the thin strip of concrete left behind. Cores close to columns are especially risky, because that’s where slabs carry the highest shear.
Do this instead: Get the layout checked by the structural engineer. If several services need to pass through one area, a single planned opening may be safer than a row of cores.
Mistake 3: Coring into beams or columns without approval
What happens: A beam or column is in the way, so the crew cores through it.
Why it damages the structure: Beams and columns are primary load-carrying elements. A hole in the wrong place can cut main bars or remove concrete the element needs to resist load.
Do this instead: Treat beams and columns as off-limits unless an engineer approves the exact location and size. We cover this in more detail in our guide to coring through beams and columns.
Mistake 4: Letting the bit blow out the underside
What happens: As the bit breaks through, it pushes a chunk of concrete off the soffit below. The hole on the underside ends up ragged and much bigger than planned.
Why it damages the slab: That blow-out, or spalling, can expose bottom reinforcement and reduce cover. Exposed steel corrodes, especially in the UAE’s humid coastal air, and the damage spreads over time.
Do this instead: Ease off feed pressure as the bit nears breakthrough. On finished soffits, the crew can drill partway from each side or fix a backing board below. Never force the bit to speed things up.
Mistake 5: Letting the core drop
What happens: The core breaks free and falls to the floor below.
Why it damages the slab and more: A 150mm core through a 250mm slab weighs over 10kg. Larger cores weigh far more. A falling core can crack a lower slab finish, damage services or ceilings, or injure someone below.
Do this instead: Barricade the area below, and secure or catch the core before final breakthrough. For large cores, use a retaining method so the core is pulled up rather than dropped.
Mistake 6: Leaving holes and cut bars unsealed
What happens: The core is done, the pipe goes in later (or never), and the gap around it is left open.
Why it damages the slab: Cut rebar ends are exposed to moisture and start to rust. Rust expands, cracks the concrete around it and causes spalling. Open holes also let water travel between floors and let fire and smoke spread, which breaks the fire separation the slab is meant to provide.
Do this instead: Seal or sleeve every core promptly. Treat cut bar ends where they’re exposed. Use the right firestop system around services that pass through fire-rated slabs. If damage has already started, concrete repair stops it from spreading.
The common thread
None of these mistakes are about the drill itself. They come from skipping steps: no scan, no engineer, no plan for what happens below or after.
A good coring crew handles all of it as one job.
Get core cutting done right
Scan and Core scans, cores and seals across Dubai and Abu Dhabi, with structural checks when the location needs one. See our concrete cutting and coring services, or contact Scan and Core to book a site visit. You can also call +971 56 861 9006.
