Concrete scanning before drilling or coring is used to reduce the risk of striking reinforcement, post-tensioning tendons, embedded services, ducts and other concealed features within a concrete element.
The survey is commonly required before installing anchors, forming service penetrations, extracting concrete cores, cutting openings or carrying out structural alterations. It helps the project team understand what may be present beneath the surface and identify lower-risk positions for the proposed intrusive work.
A scan should not be treated as a simple box-ticking exercise. The survey must be planned around the actual hole diameter, drilling depth, concrete element, structural arrangement and service risk. A small fixing hole and a 150mm core require different survey areas and different levels of control.
UK construction worker operating a concrete core drilling rig on a wet construction site
The key message is this: concrete scanning reduces uncertainty before drilling or coring, but it does not guarantee that a location is completely clear. The scan should form part of a wider process that includes design approval, service information, permits, controlled drilling and clear responsibility for authorising the work.

Why Is Concrete Scanning Required Before Drilling or Coring?

Drilling into an existing concrete structure creates several possible risks. The drill may strike reinforcement, damage a tendon, penetrate a live service, cut through an embedded pipe or weaken a structural zone that was not intended to be altered.
Concrete scanning helps reduce these risks by identifying concealed responses before intrusive work begins. The survey can support decisions about whether a proposed location is suitable, whether the hole should be moved or whether further investigation is required.
Typical reasons for scanning include:
  • Installing mechanical or resin anchors.
  • Drilling fixings for façade supports or secondary steelwork.
  • Forming mechanical and electrical service penetrations.
  • Extracting concrete cores for laboratory testing.
  • Creating openings through slabs or walls.
  • Installing temporary works connections.
  • Fixing handrails, barriers or plant supports.
  • Drilling into post-tensioned slabs.
  • Carrying out structural investigations or breakouts.
The scanning scope should reflect the consequence of striking a concealed feature. Drilling into a lightly reinforced non-structural upstand is not the same risk as drilling into a post-tensioned transfer slab or a wall containing major services.

What Should Be Detected Before Drilling?

The survey should be planned around the concealed features that could affect the proposed work.
Feature Why It Matters Possible Consequence of Damage
Steel reinforcement Reinforcement contributes to structural strength, crack control and load transfer. Loss of steel area, reduced capacity, durability problems or need for repair.
Post-tensioning tendons Tendons contain stored force and form part of the structural system. Sudden release of energy, serious injury and structural damage.
Electrical conduits Conduits may contain live power, lighting, fire alarm or data cables. Electric shock, fire, service interruption or equipment damage.
Water or heating pipes Pipes may be pressurised or connected to occupied areas. Flooding, burns, water damage or disruption to building systems.
Tendon ducts or embedded sleeves These may be confused with services or reinforcement. Damage to structural or service systems and uncertainty over repair.
Cast-in channels or plates These may form part of façade, structural or restraint systems. Loss of usable anchorage or damage to an existing connection.

Which Scanning Methods Are Used?

Ground-penetrating radar and electromagnetic reinforcement detection are the most common methods used before drilling or coring.
Ground-penetrating radar can help identify reinforcement, tendons, service ducts, interfaces and some non-metallic features. It is particularly useful where the survey needs to investigate more than steel reinforcement alone.
Electromagnetic cover meters are primarily used to locate ferrous reinforcement and estimate concrete cover. They can be useful for confirming shallow bar positions where the reinforcement arrangement is not heavily congested.
The methods may be used together. GPR may provide the wider concealed arrangement, while a cover meter may help refine the location of shallow steel.
A Clear Scan Is Not an Absolute Clearance Certificate
A scanner can only detect features that produce a recognisable response under the actual site conditions. Small, deep or masked objects may not be visible. The result should be used to reduce risk and guide controlled drilling, not to remove all other project controls.

How Large Should the Survey Area Be?

The survey area should be larger than the nominal hole. This allows the operator to identify the direction and continuity of nearby features and gives the project team space to relocate the proposed drilling position.
The required area depends on:
  • The number of holes.
  • The hole diameter.
  • The proposed drilling depth.
  • The spacing between holes.
  • The size of the drill or coring rig.
  • The expected reinforcement arrangement.
  • Whether post-tensioning or services are present.
  • The amount of permitted relocation.
Scanning only the exact centreline of a proposed hole may not show whether a nearby response is a bar crossing the hole, a tendon running beside it or a service changing direction.
A wider grid gives the operator more context and normally improves confidence in the interpretation.

Why the Hole Diameter Matters

A location that is suitable for a small 12mm fixing may not be suitable for a 100mm or 150mm core. The full diameter of the opening must fit between identified features with any required structural clearance.
The survey should consider:
  • The nominal hole diameter.
  • The external diameter of the core barrel.
  • Possible drill wander.
  • Required edge distance from reinforcement or tendons.
  • Space needed to position and restrain the drilling equipment.
  • The consequences of local breakout around the opening.
The person requesting the scan should state the actual drilling or coring dimensions. A vague request to “scan this point” does not provide enough information for a reliable clearance assessment.

Why the Drilling Depth Must Be Confirmed

The drilling depth determines which concealed layers matter. A shallow anchor hole may only interact with the first reinforcement layer, while a core through the full slab depth may pass through several reinforcement layers, services or tendons.
The scanning technician should know whether the work involves:
  • A shallow fixing hole.
  • A partial-depth recess.
  • A full-depth core.
  • A chase or saw cut.
  • A stepped or angled hole.
  • A hole that must stop before the opposite face.
A position may appear clear near the surface but contain a deeper bar or service. The scan must therefore be interpreted against the full proposed drilling depth.

Scanning from One Side Versus Both Sides

Where access is available, scanning from both faces can improve the investigation of thick or heavily reinforced elements.
For example, a slab may be scanned from the top surface to identify top reinforcement and from the soffit to investigate the lower reinforcement layer. This can be particularly useful where strong shallow responses mask deeper features.
Two-sided access may also help confirm element thickness and compare the position of identified features.
Where only one face is accessible, the limitation should be recorded clearly in the survey report.

Scanning Before Drilling into Post-Tensioned Concrete

Drilling into post-tensioned concrete requires a higher level of control because tendons contain stored force and form part of the structural system.
The survey should not be limited to a narrow strip around the proposed hole. Suspected tendons should be traced across a wider area so their direction and continuity can be understood.
The project team should provide:
  • Post-tensioning drawings where available.
  • Details of banded or distributed tendon zones.
  • Known anchorage locations.
  • The intended drilling depth and diameter.
  • The structural engineer’s approval for the proposed penetration.
  • A controlled drilling method.
Support zones, anchor zones and tendon bands may contain heavy reinforcement and several overlapping features. These areas can be difficult to interpret and may be unsuitable for intrusive work.
A scan should not be described as proving that a post-tensioned slab is safe to drill. It provides evidence to support a controlled decision by the responsible engineer and contractor.

Scanning for Embedded Services

Concrete scanning can identify many embedded service routes, including metallic conduits, larger pipes and some plastic ducts. However, service detection within concrete has limitations.
The scanner may detect a concealed linear response without confirming:
  • What service the route contains.
  • Whether it is live.
  • Whether it is pressurised.
  • Whether it is active or abandoned.
  • Whether it changes depth between scan lines.
Concrete scanning should therefore be used alongside available service drawings, electrical detection, isolation information and site permit procedures.
Where the consequences of striking a service are significant, the project team may need to isolate the system or confirm its location through another method before drilling.

Can a Concrete Scanner Confirm a Safe Drilling Position?

A concrete scanner can help identify a lower-risk position, but it cannot provide an absolute guarantee that the proposed drilling line is free from every concealed feature.
A suitable drilling location should normally satisfy several conditions:
  • No clearly detected reinforcement or tendon crosses the required hole diameter.
  • No suspected service route crosses the drilling path.
  • The position is structurally acceptable to the designer.
  • The required hole depth has been considered.
  • The area is accessible for safe drilling equipment setup.
  • The drilling method includes controls for unexpected resistance or concealed objects.
The survey technician identifies and marks evidence. The structural engineer, designer or responsible contractor normally decides whether the penetration is acceptable.

Concrete Scanning and the Permit-to-Drill Process

Concrete scanning should normally form part of a documented permit-to-drill or permit-to-core process.
The permit process may include:
  • Confirmation of the approved hole location.
  • Structural approval where required.
  • Review of reinforcement and post-tensioning information.
  • Review of service drawings.
  • Confirmation of isolation where applicable.
  • Concrete scanning and surface marking.
  • Photographic evidence of the scan.
  • Maximum drilling depth.
  • Approved drilling equipment and method.
  • Authorisation by the responsible person.
The permit should link the scan result to the exact physical location. If the drilling position is moved after scanning, the revised position should be checked and authorised before work continues.

What Should Be Marked on the Concrete?

Surface markings should be clear, durable enough for the planned work and understood by the drilling team.
The operator may mark:
  • Detected reinforcement lines.
  • Possible tendon routes.
  • Possible service routes.
  • Areas of uncertainty.
  • Approved or proposed hole centres.
  • No-drill zones.
  • The survey grid or reference point.
Different colours should have a defined meaning. The drilling team should not be left to guess whether a line represents reinforcement, a service, a tendon or a safe zone.
Photographs should be taken before drilling because chalk and tape can be removed, covered or displaced.

What Should the Survey Record Include?

  • Project name and site location.
  • Date of scanning.
  • Concrete element and exact survey area.
  • Purpose of the proposed drilling or coring.
  • Hole diameter and depth.
  • Equipment and scanning method used.
  • Accessible survey face.
  • Surface finish and condition.
  • Identified reinforcement and estimated depths.
  • Possible tendons, ducts or services.
  • Areas of uncertain interpretation.
  • Marked drilling location.
  • Photographs and reference dimensions.
  • Limitations of the survey.
Where only surface marking is requested, the project should still retain enough photographic and location evidence to demonstrate what was scanned and where the work was authorised.

Controlled Drilling After Scanning

The drilling method should reflect the remaining uncertainty after scanning. Appropriate controls may include:
  • Using a defined maximum drilling depth.
  • Beginning with a smaller pilot hole where suitable.
  • Using depth stops.
  • Monitoring changes in resistance.
  • Stopping immediately if metal, voiding or unexpected material is encountered.
  • Avoiding percussion where this could increase risk.
  • Using water or dust controls appropriate to the location.
  • Maintaining communication with the permit issuer.
Scanning is most effective when the findings are integrated into the drilling method rather than treated as a separate activity completed earlier.

Concrete Scanning Before Core Sampling

Concrete cores are often extracted to determine compressive strength, composition, depth, condition or other material properties. The core location may need to avoid significant reinforcement while still being representative of the element under investigation.
Before coring, the survey should identify:
  • Primary and secondary reinforcement.
  • Possible tendons or ducts.
  • Embedded services.
  • Element thickness.
  • Nearby edges, joints or structural discontinuities.
  • A suitable representative test location.
The lowest-reinforcement location is not automatically the best sampling location. The engineer may need the core to represent a particular pour, structural zone or concrete condition.
Core positions should therefore be selected jointly from both testing and structural considerations.

Concrete Scanning Before Anchor Installation

Anchors must normally be installed to a defined embedment depth and with specified spacing and edge distances. Reinforcement or services may prevent the anchor from being installed at its intended position.
The scan should cover the complete fixing pattern rather than each hole in isolation. This allows the operator to identify whether the pattern can be shifted or rotated to avoid concealed features.
The anchor designer or responsible engineer should confirm whether reinforcement may be drilled through. In most cases, reinforcement should not be cut without specific approval.
If the fixing pattern is changed after scanning, the revised arrangement should still satisfy the design requirements for spacing, edge distance and load transfer.

Common Mistakes Before Drilling or Coring

Mistake Why It Is a Problem Better Approach
Not providing the hole diameter. The operator cannot confirm whether the full opening fits between identified features. Provide the nominal and external drilling dimensions.
Not providing the drilling depth. Deeper reinforcement or services may not be considered. State the full required penetration depth.
Scanning only the exact hole centre. The direction and continuity of nearby features cannot be traced. Scan a wider surrounding grid.
Drilling at a moved location without rescanning. The new position may contain unidentified reinforcement or services. Scan and authorise the revised location.
Assuming no response means no object. Deep, small or masked features may not be visible. Use scanning as one part of a controlled drilling process.
No structural approval. A hole may avoid reinforcement but still be structurally unacceptable. Obtain approval from the responsible engineer where required.
Treating the scan as service isolation. The scanner does not confirm whether a service is live or pressurised. Use service records and isolation procedures.

Checklist Before Concrete Drilling or Coring

  • Purpose: confirm why the hole or core is required.
  • Element: identify the slab, wall, beam, column or foundation.
  • Hole diameter: provide the complete required opening size.
  • Drilling depth: confirm whether the work is partial or full depth.
  • Location tolerance: confirm how far the hole may be moved.
  • Structural approval: obtain the required design authorisation.
  • Post-tensioning: confirm whether tendons are present or suspected.
  • Service drawings: review available service information.
  • Isolation: isolate relevant services where required.
  • Survey area: scan a wider area than the nominal hole.
  • Scan direction: use perpendicular survey lines where possible.
  • Markings: ensure the meaning of all marks is understood.
  • Photographs: record the scan and approved drilling location.
  • Permit: issue a permit linked to the exact location and depth.
  • Drilling controls: use depth stops and stop-work rules for unexpected conditions.

What Concrete Scanning Does Not Replace

Concrete scanning does not replace:
  • Structural design approval.
  • Post-tensioning drawings and specialist advice.
  • Service drawings and isolation procedures.
  • Permit-to-drill controls.
  • Competent drilling operatives.
  • Appropriate RAMS.
  • Controlled drilling and stop-work procedures.
  • Physical verification where the scan is inconclusive.
The strongest approach is to combine scanning evidence with the wider project information and controls required for the specific structure.

Evidence-Based Summary

Concrete scanning before drilling or coring helps locate reinforcement, tendons, services and other concealed features.
The scan should be planned around the actual hole diameter, drilling depth, survey area and consequence of striking a concealed object.
A clear scan reduces risk but does not guarantee that every concealed feature has been detected.
Post-tensioned concrete and service-containing elements require additional controls, drawings and responsible approval.
Scanning should form part of a documented process that includes structural review, service checks, permits, clear surface marking and controlled drilling.

FAQ: Concrete Scanning Before Drilling or Coring

Should concrete be scanned before drilling?
Scanning is advisable where reinforcement, post-tensioning or embedded services may be present. The project risk assessment, specification and permit process should determine when it is required.
Can concrete scanning guarantee a clear drilling position?
No. Scanning reduces uncertainty but cannot guarantee that every small, deep or masked feature has been detected. Controlled drilling procedures should still be used.
How much area should be scanned around a core hole?
The area should be larger than the proposed core so nearby features can be traced and alternative positions considered. The required size depends on the core diameter, depth and structural complexity.
Why does the scanning technician need the hole depth?
The depth determines which reinforcement layers, tendons or services could be affected. A location that is clear at shallow depth may contain deeper concealed features.
Can reinforcement be drilled through?
Reinforcement should not normally be cut or drilled without approval from the responsible structural engineer or designer. Scanning identifies its position but does not authorise its removal.
Can GPR find electrical cables in concrete?
GPR may identify conduits or cable routes, but it does not normally confirm whether they are live. Service drawings, isolation information and other detection methods may still be required.
Is it safe to drill into a post-tensioned slab after scanning?
Scanning can help identify tendon routes, but drilling should only proceed through a controlled process with structural approval, post-tensioning information and an appropriate method statement.
Should the area be rescanned if the hole location changes?
Yes. A revised position may contain reinforcement, tendons or services that were not assessed for the original location.
Can concrete scanning replace a permit to drill?
No. Scanning should support the permit process. The permit confirms the approved location, depth, service controls, structural approval and drilling method.
What should happen if the scan is inconclusive?
The area should not be treated as clear. The position may need to be moved, scanned from another face, investigated using another method or confirmed through controlled intrusive work.
Who approves the final drilling position?
The responsible designer, structural engineer or contractor should approve the location in accordance with the project procedure. The scanning technician provides investigation evidence rather than structural approval.

Source Context and Editorial Note

This article is a STRUCTinspect technical explainer covering concrete scanning before drilling, coring, anchor installation and structural alteration.
It provides general construction information rather than a project-specific drilling procedure. Survey equipment, coverage, scan direction, drilling controls and approval requirements should be selected for the particular structure and proposed work.
This article does not provide structural engineering, post-tensioning, service detection, health and safety, contractual or construction advice. Drilling, cutting, coring and structural alteration should be reviewed and authorised by the appropriate designer, structural engineer, contractor or competent professional responsible for the works.