Most core drilling in Dubai happens inside a fit-out programme: MEP penetrations through a tower floor, drainage for a restaurant unit, riser openings in a hotel refurbishment. The slab is usually post-tensioned, the drawings are usually not the as-built, and the crew is usually waiting. A GPR scan is the step between the marked-up drawing and the core barrel, and it goes faster when everyone knows what it involves.
This guide covers what to have ready, what happens on site, how to read what we leave behind, and what the report contains. It is written from how we run GPR concrete scanning in Dubai, but the same sequence applies anywhere in the UAE.
Why the scan comes before the core
Three things in a slab can turn a routine core into a problem. Post-tension tendons are the serious one: each strand is stressed to roughly 140 to 200 kN, and cutting one releases that force at once and takes the tendon out of service along its full length. Main reinforcement is the second: cutting a bar is not a collapse risk in most cases, but it is a structural decision your engineer should make, not the core driller. Embedded conduits are the third: a live cable in a conduit is a safety risk to whoever is holding the drill.
A drawing tells you where those things were meant to go. Tendons are laid by hand into a curved profile and shifted during the pour to clear sleeves and congestion, so the real position wanders. Later fit-outs add conduits that nobody records. The scan measures where they are now. For what happens when a tendon is cut, see what happens if you cut a post-tension cable.
What to have ready before we arrive
Almost all lost time on a scanning visit comes from access and missing information, not the scan itself. Before the visit, have these sorted:
- The proposed core positions marked on the slab, or a drawing we can set them out from. A centre mark with the diameter written next to it is enough.
- Core sizes and the number of holes, and which ones can move and by how much. A drainage core that can shift 100 mm is a different conversation from a fixed sleeve position.
- Whatever drawings you have, even if you do not trust them. Structural and PT layouts help us interpret what we see.
- Access booked: goods lift, loading bay, parking, and the building's work permit if one is needed. Most Dubai towers and malls want the permit issued before any contractor works on the slab.
- The floor clear around each position. Stored material, pallets and furniture over the scan area have to move, because the antenna is rolled across the surface.
- The floor finish noted. Radar passes through tiles and screed, but not through metal, so steel decking or foil-backed membranes change what is possible.
- Someone on site who can make a decision if a position cannot be cleared.
Six lines on WhatsApp before the visit, covering site, floor, number and size of cores, how spread out they are, finish, and date, is usually enough for a fixed price and a realistic time on site.
Mark a zone, not a point
We scan the area around each position, not just the centre of the hole. A tendon 80 mm from your centre mark is a problem for a 150 mm core. A tendon 300 mm away is not, but only if the core stays where it was marked. Scanning a zone also tells you where the nearest clear position is if the planned one is blocked, which saves a second visit.
If your positions are clustered, say a group of drainage cores in one wet area, we grid scan the whole zone in one pass and clear every position within it. That is quicker and cheaper than scanning hole by hole, and it is the reason scanning is priced on area rather than on the number of holes.
What happens on the day
The operator sets out a grid over each zone and rolls the Proceq GP8000 along the grid lines in both directions. The radar shows reflections live on the screen as it moves, so tendons, bars and conduits can be marked on the concrete straight away rather than after processing. For a few positions in one area, the visit is typically one to two hours including set-up and marking. A full floor plate takes longer, and we tell you how long when we quote.
Because GPR uses no radiation, nobody has to clear the floor below and work can continue nearby. That matters in Dubai, where much of this work happens in trading malls, live hotels and occupied office towers.
Reading the marks we leave
Before we leave, the operator walks your foreman through the marks: which lines are tendons, which are bars or conduits, and which positions are cleared for coring. Ask questions at that point, while the operator is still on the floor and can rescan if anything is unclear.
Protect the marks. Floor marking gets scuffed by trolleys and cleaned off by other trades, and a cleared position that has lost its marks is no longer cleared. If the coring is not happening the same day, tell the other trades the area is marked, or photograph the marks against the grid so they can be reinstated.
When a position cannot be cleared
Sometimes a tendon band runs exactly where the core is drawn. When that happens we stop and tell you before anything is cut. In most cases the position can shift a short distance and we mark the nearest clear alternative so your crew can continue the same visit.
Where a position cannot move, such as a fixed sleeve, a structural opening or a riser that has to align floor to floor, it becomes a design question for your engineer or consultant. We give them the scan data to make that decision. What we will not do is core through it and report afterwards.
What the report shows
Within 24 hours of the visit you receive a PDF report: a marked-up layout of the scanned area, the position and depth of the tendons, bars and conduits we found, the positions we cleared, and any limits that applied, such as congested reinforcement over a column. 3D scan data is available on request for consultants who want it. Many Dubai buildings ask for this report before signing off the coring permit. For a section-by-section walk through, see what is in a GPR survey report.
Mistakes that undo a good scan
- Moving the core after the scan. A position cleared at one point is not cleared 200 mm away. If the position changes, call us back or scan the new zone.
- Changing the diameter. A 100 mm core that was cleared is not automatically clear at 200 mm.
- Relying on an old scan. Penetrations made since, or a scan of a different bay, do not clear today's position.
- Scanning a sample. On a post-tensioned slab every penetration needs scanning, because the one you skipped is the one that finds a tendon.
- Letting the marks disappear before the cut.
Scan and core in one visit
If you would rather not coordinate two contractors, we can do both: scan with the GP8000, mark, then core from 12 mm to 500 mm in the cleared positions, with slurry contained. See core cutting in Dubai. If your project is outside Dubai, our GPR concrete scanning page covers the other emirates. For how we locate tendons specifically, read post-tension cable detection in UAE slabs.