What Is In-Slab Concealment Anchoring? (Wedge Bolts)
In-slab anchoring is the fastening of a fixture to a concrete floor with a mechanical expansion anchor, such as a wedge anchor. The anchor expands inside a drilled hole to resist movement. Safe design depends on the exact anchor, slab, loads, and local code. “Concealment anchoring” is not a separate standard method; the connection must remain accessible for inspection and service.
The idea behind a wedge anchor follows a long-used fastening principle: an inserted part expands against its base material to hold a load. In concrete, that simple action has strict limits. A secure-looking bolt can still fail if the slab is thin, cracked, damaged, or drilled near an edge. I treat the anchor and concrete as one connection, not as separate parts.
Planning: Slab Survey, Loads, and Anchor Selection
Before choosing an anchor, establish what the slab is made of, what the fixture must carry, and how the load reaches the floor. A wedge anchor is suitable only when its product approval, the concrete condition, and the design checks support that use. Start with the slab and the load, not a bolt size chosen by habit.
A wedge anchor is a mechanical anchor with a threaded stud and an expansion component. As the anchor is set, the component presses against the sides of the hole. This creates resistance to pullout and sideways movement, but it does not make every slab or load suitable.
First identify the intended load. A fixed machine, guardrail, storage rack, or base plate may place different forces on its anchors. Tension pulls the anchor out of the slab; shear acts across it. Loads can combine, and repeated movement or vibration may also matter. Use a qualified designer when the fixture is safety-critical, supports people, or has substantial or changing loads.
Then confirm the exact anchor type. “Wedge bolt” is sometimes used informally, but products that sound similar may have different approval limits and installation steps. Check the current instructions and evaluation report for the specific model. ICC-ES AC193 is an acceptance criterion used to assess mechanical anchors in concrete; it is not a capacity rating for every product.
ACI 318, Chapter 17, covers design checks for anchors to concrete, including tension, shear, edge distance, spacing, and possible concrete failure. Apply the edition adopted by the local jurisdiction. ASTM E488/E488M describes test methods for anchor strength in concrete and masonry; it does not provide one universal capacity that can be applied to any installation.
| Planning item | What to establish | Why it matters |
|---|---|---|
| Anchor model | Product, diameter, and approval report | Values and permitted uses vary by model |
| Slab | Thickness, condition, and concrete type | The concrete can govern the connection’s strength |
| Load | Tension, shear, and any combined or repeated action | Anchor design must match how the fixture is loaded |
| Layout | Hole locations, spacing, and distance to edges | Nearby holes or edges can affect concrete failure |
| Drilling zone | Reinforcing steel and embedded services | Drilling can damage the building or create serious hazards |
A useful selection record lists the fixture, estimated loads and their source, anchor model, slab information, and the checks still needed. If key details are unknown, pause and get drawings, a scan, or professional review. Do not fill gaps with a larger anchor or a guessed capacity.
Access and Clearances: Edge Distance, Embedment, and Embedded Services
Clearance is not just room for a drill. It includes the required distance from slab edges and nearby anchors, the embedment depth, the slab thickness, and the space needed to install and inspect the fixture. All these values are product- and design-specific. No generic number can replace the anchor report and the slab check.
Edge distance is the distance from an anchor center to the nearest concrete edge. Spacing is the distance between neighboring anchors. Embedment is the depth the anchor sits in the concrete. These dimensions affect how forces spread through the slab, so a layout that fits the base plate may still fail design checks.
Measure and record the planned hole locations before drilling. Compare each measurement with the exact anchor’s current evaluation report and instructions, then check the layout under the applicable code. Also verify that the slab thickness meets the product requirements. Do not assume that a thick floor finish means the concrete below is thick enough.
The most serious hidden hazard is a post-tensioned slab. A drilled hole that cuts a tendon can cause severe injury or structural failure. Do not drill until tendon locations are established and the proposed holes are approved. A rebar detector alone may not reliably find tendons or every embedded service.
Review structural drawings where available, and use suitable scanning methods to locate post-tensioning, reinforcing steel, conduit, and piping. A scan helps inform the decision; it does not by itself approve a hole. If records conflict with scan results, or the slab type is unclear, stop and ask a qualified structural professional or the responsible building authority.
Execution: Drilling, Hole Cleaning, and Anchor Setting
Good installation starts only after the slab and hole locations are cleared for drilling. Use the bit, diameter, depth control, cleaning steps, and setting method specified for the chosen anchor. Small errors can change how the anchor engages concrete. Follow the manufacturer’s current instructions rather than applying a familiar routine from a different product.
- Mark the approved locations. Check measurements against the fixture layout and the verified service scan. Confirm that the drill can stay square and reach the required depth without hitting a blocked area.
- Use the specified drill and bit. Match the bit type and diameter to the anchor instructions. Control hole depth as directed; do not drill deeper or wider by assumption.
- Clean the hole as instructed. Dust left in a hole can affect setting. Use the cleaning method and sequence specified for that anchor. Do not substitute a method from another product.
- Set the anchor as directed. Insert and set it using the specified tool and procedure. If the instructions call for a torque value, use only the value for that exact model and installation condition.
- Fit the fixture and inspect. Check that the fixture sits as intended, the anchor is seated correctly, and the surrounding concrete shows no visible damage.
Hole diameter, hole depth, anchor embedment, minimum slab thickness, and installation torque are not universal wedge-anchor values. They must come from the exact product instructions and evaluation report, together with the design. If a hole breaks out, lands on steel, or is drilled in the wrong place, do not simply move the anchor nearby. Recheck spacing and edge distance before making any change.
Verification: Inspection, Documentation, and Code Compliance
Verification means confirming that the installed anchor matches the approved design and product instructions, and that the concrete remains sound. It is not a quick pull by hand. Record the installation details before the area is covered, and arrange any inspection or testing required by the project documents, code, or authority having jurisdiction.
The check should compare the installed work with the design: anchor model and size, location, embedment, hole preparation, setting method, and fixture fit. Look for cracked or spalled concrete, a tilted anchor, damaged threads, or a base plate that does not seat as planned. If anything differs from the approved details, ask the designer or manufacturer for direction before loading the fixture.
Proof testing may be required in some projects, but it is not automatically required for every wedge anchor. The test method, sample size, acceptance criteria, and responsible inspector must come from the project requirements or qualified design professional. ASTM E488/E488M is a test method, not a substitute for a project-specific test plan or design.
Keep a record with: – Anchor manufacturer, model, and product report – The applicable code edition and design reference – Slab details and scan or drawing records – Hole locations and measured installation details – Required inspection or test results – Any deviations and written approval for them
Do not finish over an installation in a way that blocks required inspection, maintenance, or access. Where a finish must be restored, first complete and document the checks required for the project.
Worked Scenarios: How the Checks Change
These examples are illustrative planning scenarios, not reports of completed jobs or anchor recommendations. In each case, the right choice depends on verified slab details, the loads, and the exact product documentation. The practical lesson is to resolve uncertainty before drilling.
A light equipment base on a known slab: The installer has drawings, a known anchor model, and a defined fixture load. The next step is to check the product report and the design for the required embedment, spacing, edge distance, and concrete condition. “Light” does not remove those checks.
A rack planned near a slab edge: The base plate fits, but one anchor would sit close to the edge. The installer should not move the hole a few centimeters and proceed by eye. The revised layout must be checked for edge distance, spacing, and anchor-group behavior under the actual loads.
A proposed hole in an older apartment floor: The slab type and embedded services are unknown. The safe next step is to locate drawings and arrange appropriate scanning and review. If post-tensioning cannot be ruled out, drilling should not proceed until the proposed hole is cleared and approved.
In all three scenarios, the installation decision turns on evidence: product instructions, slab information, and design checks. Guessing at a torque or moving an anchor to a convenient spot does not replace that work.
FAQ: Wedge Anchors in Concrete Slabs
These answers cover common questions about wedge anchors in accessible concrete installations. The short answer is that product-specific instructions and the adopted code govern the details. If the slab, load, or drilling zone is uncertain, pause and get qualified review before drilling.
What is in-slab concealment anchoring?
The phrase is not a standard anchor category. It usually refers to fastening a fixture to a concrete slab with an anchor, such as a wedge anchor. The connection should remain accessible where inspection or service is required.
How does a wedge anchor work?
A wedge anchor expands against the wall of a drilled concrete hole when set. That contact helps resist pullout and sideways force. Its capacity depends on the anchor, concrete, layout, and load.
Is a wedge bolt the same as a wedge anchor?
Not always. People may use “wedge bolt” as a general term, but product names and designs vary. Identify the exact product and follow its current instructions and evaluation report.
Can I use the same torque for every wedge anchor?
No. Installation torque, when specified, is product-specific. Use the value and method for the exact anchor model; do not rely on a generic chart or another product’s instructions.
How close can a wedge anchor be to a slab edge?
There is no universal edge-distance value. Check the exact anchor report and the design under the locally adopted code, including the slab and the applied loads.
Can I drill into a post-tensioned slab?
Only after tendon locations are established and the proposed hole is approved. Cutting a tendon can cause severe injury or structural failure. A rebar detector alone may not reliably locate post-tensioning.
Does ASTM E488/E488M tell me the anchor’s capacity?
No. It describes test methods for anchors in concrete and masonry. Use the specific product evaluation and the applicable design checks to establish suitability.
Should every wedge anchor be proof tested?
Not automatically. Testing depends on project documents, code, and design requirements. A qualified person should set the method and acceptance criteria when testing is required.
What should I do if the drill hits steel?
Stop. Do not force the bit, cut the steel, or shift the hole without review. Confirm what the steel is and whether a revised location meets spacing and edge-distance requirements.
Can I cover the anchor after installation?
Only after required inspection, documentation, and testing are complete. Do not block access that the project requires for inspection or maintenance.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
