Cutting or coring concrete looks routine, but it carries real risks: cutting a post-tensioned tendon or live conduit, weakening a structural member, exposing workers to silica dust, and flooding or contaminating spaces below. Safe work starts before the saw arrives, with structural approval, scanning, and a plan for dust, water, noise and the people around the work.
Before the saw arrives
1. Confirm the cut is structurally acceptable
Every opening in a slab, wall, beam or column removes material and may cut reinforcing. Before cutting:
- Review the structural drawings to understand the structure, including whether slabs are post-tensioned.
- Have a structural engineer review and approve new openings, especially larger openings, cores near columns or beams, and any cut in a structural member.
- Get any required building permit; many municipalities require one for structural alterations.
Small cores in a conventionally reinforced slab may be routine, but the decision should still be made by someone qualified, not assumed by the cutting crew.
2. Scan before you cut
Scanning locates reinforcing, tendons, conduit and pipes so the cut can avoid them. The two common methods are X-ray and ground penetrating radar, each with strengths and limits. See concrete X-ray vs GPR scanning.
- Mark proposed core and cut locations before scanning
- Scan both the location and a margin around it
- Mark detected items clearly on the surface
- Move cores or cuts away from detected items where possible
- Keep scan results with the job records
Post-tensioned slabs need extra care. Tendons are under very high tension. Cutting one can release energy violently, injure workers and weaken the slab. If a slab is or may be post-tensioned, involve a structural engineer, locate tendons precisely and keep cuts well clear of them.
3. Isolate services
Even after scanning, treat embedded services as possibly present:
- Identify electrical circuits that might pass through the area and have them isolated under your lockout procedures. See lockout and tagout.
- Check for water, gas, drain and fire protection piping below or within the slab.
- Check what is directly below: occupied spaces, equipment, electrical rooms or data rooms.
While cutting
4. Control silica dust
Concrete contains crystalline silica. Cutting, coring and grinding it creates respirable silica dust, which can cause silicosis, lung cancer and other diseases. Occupational exposure limits apply in every province, and employers must control exposure.
Use the hierarchy of controls:
- Wet methods: water fed to the blade or bit is the most common control for coring and sawing.
- Local exhaust: tools with shrouds connected to a suitable vacuum with an appropriate filter.
- Work planning: isolate the area, keep others away, and clean up with wet methods or suitable vacuums, never dry sweeping or compressed air.
- Respiratory protection: where controls don't reduce exposure enough, workers need respirators selected and fit-tested under a respiratory protection program. See respiratory protection programs.
5. Manage water and slurry
Wet cutting produces slurry. Plan to:
- Contain and collect slurry rather than letting it flow into drains, which may be prohibited
- Protect spaces below from water coming through the core
- Keep water away from electrical equipment and use ground fault protection on cords and tools
- Prevent slips with drainage and cleanup
6. Protect people around the work
- Barricade and sign the work area, above and below
- Plan for the core or cut section falling: support or catch it
- Manage noise and vibration, and tell occupants when work will happen
- Provide hearing, eye and face protection
- Make sure cut sections are handled with safe lifting methods
- Leave guarded or covered any new opening in a floor
New floor openings are a fall hazard. Cover or guard them immediately, and mark covers clearly.
After cutting: check the finished work
After cutting, check the opening matches what was approved, inspect for cut reinforcing that wasn't expected, and report anything unusual to the engineer. Firestop penetrations through rated slabs and walls, since an unsealed core is a breach in a fire separation.
A sign-off sequence before cutting
Many sites use a simple permit or sign-off sheet so no step is skipped. A practical sequence, with what to record at each step:
- Location approved. Record who approved the opening, with a reference to the drawing or engineer's sketch.
- Scan completed. Record the method, the technician, the date and where the results are kept. Photograph the markings.
- Services isolated. Record which circuits or lines were isolated and the lockout details.
- Below checked and closed. Record who checked the space below, how it is barricaded, and how equipment is protected from water.
- Dust and water controls ready. Note the control method, the vacuum and filter used, and respirators if required.
- Opening protected. After cutting, record how the opening is covered or guarded and when firestopping will be done.
The sheet takes a few minutes and gives the building owner a record of how each opening was made.
Common mistakes
- Moving the core after scanning. A location shifted on the day, even a short distance, may no longer be in the clear zone. Re-scan if it moves.
- Forgetting the floor below. Water, slurry and the core itself end up somewhere. Check that space every time.
- Dry cutting to save time. It creates far more respirable silica dust than wet methods.
- Leaving cores unsealed. An open penetration through a rated floor breaches the fire separation until it is firestopped.
A typical case
A tenant in an office tower needs several cores for new data cabling between two floors. The drawings show the slab is post-tensioned. A structural engineer reviews the locations and approves them subject to scanning. Scanning finds a tendon band running through one of the planned locations, so that core is moved into a marked clear zone. The electrical contractor isolates a circuit that runs nearby. On the floor below, the space is closed off, a catch is set under each core, and the ceiling tiles are removed so water and slurry can be contained. The cores are drilled wet with a vacuum collecting the slurry, the openings are covered, and the firestopping contractor seals them the same week.
Who should do the work
Concrete cutting and coring should be done by trained operators using equipment in good condition. Scanning should be done by qualified technicians, and X-ray only by licensed operators. If you are a building owner or manager, your job is to make sure the planning above happens before you let anyone start.
How ehZee can help
We help owners and contractors plan concrete cutting and coring: reviewing drawings, recommending and coordinating scanning, and assessing the condition of the concrete before and after the work. See our concrete inspections and X-ray, or call 1-833-888-0091.
Common questions
Do I need scanning for a small anchor hole?
Shallow anchors in areas with known, conventional reinforcing are often installed after a scan or careful review. In post-tensioned slabs, or near conduit, scanning is strongly recommended for any drilling.
Is wet cutting enough for silica?
Wet methods greatly reduce dust, but whether they are enough depends on the task, duration and setting. Employers must assess exposure and add controls or respirators where needed.