Anchors Sizing and Use
Applies to: Any installation requiring mechanical anchoring into concrete or masonry Purpose: Field reference for anchor type selection, proper hole sizing, hole prep, and installation procedures for wedge anchors, epoxy anchors, drop-in anchors, and concrete screws Version: 1.0 | Last Updated: February 21, 2026 Owner: John Lang
Field Tips
This section is for installation tips and lessons learned. Add notes here as you encounter them in the field.
Anchor Type Overview
Use this table as a quick starting point for anchor selection. Refer to each section below for full installation procedure.
| Anchor Type | Best For | Edge Distance | Removable | Tile-Safe | Notes |
|---|---|---|---|---|---|
| Wedge Anchor | Heavy structural loads in solid concrete | Standard | No | No | Expands under torque — keep away from tile |
| Epoxy Anchor | High loads, cracked concrete, short edge spacing | Reduced OK | No | Yes | Strongly preferred through tile or stone |
| Drop-In Anchor | Flush-mount, overhead, light to medium loads | Standard | No | No | Requires setting tool — do not skip |
| Sleeve Anchor | Light to medium loads, multiple base materials | Standard | No | No | Versatile but lower load capacity |
| Concrete Screw | Light duty, adjustable or temporary mounts | Standard | Yes | No | Tapcon-style — threads directly into concrete |
⚠️ Always use the anchor type and size specified on the project drawings or by the equipment manufacturer. If drawings do not specify, contact your PM before selecting an anchor. Resellers typically supply the correct anchor hardware with the equipment — retain all extras, do not discard.
Wedge Anchors
What They Are
A wedge anchor is a one-piece, threaded bolt with an expansion clip near the bottom. When the nut is tightened, the clip expands outward and wedges against the concrete hole wall. Wedge anchors are the most common anchor for heavy equipment like turnstiles, barriers, and bollards.
Common brands: ITW Red Head TruBolt, Hilti Kwik Bolt, Simpson Strong-Tie Wedge-All, Powers Fasteners
When to Use
- Solid, uncracked concrete
- Medium to heavy structural loads
- Permanent installations
When NOT to Use
- Cracked or spalled concrete — cracks allow the wedge to slip
- Tile or stone finish floors — expansion stress can fracture the finish; use epoxy instead (see Tile & Stone Flooring Install Guide)
- Near slab edges or existing penetrations — insufficient edge distance reduces holding strength significantly
Hole Sizing
| Anchor Diameter | Drill Bit Size | Minimum Embedment | Min. Edge Distance |
|---|---|---|---|
| 3/8” | 3/8” | 1-1/2” | 1-3/4” |
| 1/2” | 1/2” | 2-1/4” | 2-1/4” |
| 5/8” | 5/8” | 2-3/4” | 2-3/4” |
| 3/4” | 3/4” | 3-1/4” | 3-1/4” |
Values above are general minimums. Always confirm with the specific anchor manufacturer’s load table for the project conditions. The anchor bolt must extend at least one thread past the nut after final torque.
Installation Procedure
- Drill the hole using an SDS rotary hammer with a carbide bit sized to the anchor diameter — see table above
- Mark embedment depth on the bit with tape before drilling
- Clean the hole — blow out dust with a blow-out tube, then vacuum; one pass is sufficient for wedge anchors
- Do not touch the inside of the cleaned hole — skin oil reduces friction
- Insert the anchor through the fixture and into the hole — the full embedment depth must be in concrete
- Thread the nut and add washer — do not omit the washer
- Torque the nut per the manufacturer’s installation torque specification
- Tighten in a cross pattern when securing a multi-anchor fixture
- Do not over-torque — you are expanding the clip in concrete, not clamping a gasket
- Verify the anchor does not rotate or pull — if it spins, the hole is oversized or the concrete is too weak
Common Failures
- Drilling oversized holes — the clip cannot expand enough to grip, often caused by a worn SDS bit
- Insufficient embedment depth — the clip ends up in the slab’s weak surface layer
- Not cleaning the hole — dust acts as a lubricant and reduces friction significantly
- Over-torquing at tile — the expansion stress cracks the finish
- Installing into cracked or spalled concrete without epoxy reinforcement
Epoxy Anchors
What They Are
An epoxy anchor (also called a chemical anchor or adhesive anchor) uses a two-part epoxy resin injected into the hole. A threaded rod or bolt is inserted while the epoxy is wet and allowed to cure. There is no mechanical expansion — the anchor holds entirely through adhesive bond. This makes epoxy anchors the preferred choice when tile integrity matters, when edge distances are limited, or when the base material is cracked.
Common systems: ITW Red Head Epcon, Hilti HIT-RE, Simpson SET-XP, Powers AC100+
When to Use
- Installations through tile or stone finish floors — no expansion stress means no risk of cracking the finish
- Cracked concrete — bond is maintained even across cracks
- Reduced edge distances where wedge anchors would fall short
- High-load applications requiring maximum pull-out strength
- Overhead or inverted installations (use an epoxy rated for overhead use)
Hole Sizing
Epoxy anchor holes are slightly larger than the threaded rod diameter to allow resin to fill the annular gap and form a full bond.
| Rod Diameter | Drill Bit Size | Minimum Embedment | Min. Edge Distance |
|---|---|---|---|
| 3/8” | 1/2” | 2-1/4” | 1-3/4” |
| 1/2” | 5/8” | 3” | 2-1/4” |
| 5/8” | 3/4” | 3-3/4” | 2-3/4” |
| 3/4” | 7/8” | 4-1/2” | 3-1/4” |
Always verify bit size with the specific epoxy system’s installation instructions — sizing varies by manufacturer.
Installation Procedure
- Drill the hole using an SDS rotary hammer with the correct carbide bit — see table above
- Mark embedment depth on the bit with tape
- Clean the hole thoroughly — epoxy bond depends entirely on a clean surface
- Blow out the hole from bottom to opening — minimum three passes
- Vacuum out remaining dust — minimum three passes
- Do not touch the inside of the cleaned hole
- Load the epoxy cartridge into the dispenser gun and prime by dispensing until the resin color is uniform — discard the mixed material used for priming
- Insert the mixing nozzle to the bottom of the hole
- Inject epoxy while slowly withdrawing the nozzle — fill from the bottom up to avoid air pockets; fill approximately 2/3 of the hole depth
- Insert the anchor rod with a slow rotating motion to the required embedment depth — excess epoxy should rise to the hole surface
- Allow full cure before loading — cure time varies significantly by temperature:
- Above 70°F / 21°C — typically 1–2 hours
- 50°F to 70°F / 10–21°C — 3–6 hours
- Below 50°F / 10°C — consult epoxy manufacturer; may require warming the concrete
- Do not disturb the anchor during cure — mark it and keep others away from the area
- Apply final torque only after full cure — torque per manufacturer specification
⚠️ Do not rush the cure. Loading an epoxy anchor before full cure will pull the anchor free without warning. When in doubt, check the cure time chart printed on the epoxy cartridge.
Common Failures
- Insufficient hole cleaning — this is the most common cause of epoxy anchor failure
- Injecting from the top instead of bottom — creates air voids in the bond zone
- Not priming the cartridge — unmixed resin at the start of the cartridge does not cure properly
- Loading before full cure — bond is not established and anchor will pull free
- Using an indoor-rated epoxy in cold conditions — cure time becomes unpredictably long
Drop-In Anchors
What They Are
A drop-in anchor (also called an internal anchor or shell anchor) is a thin-walled cylindrical sleeve with an internal expansion cone. It is set flush with or slightly below the concrete surface. A setting tool is required — the anchor cannot be set without it. Drop-in anchors provide a female threaded socket, so a bolt threads directly into the anchor rather than being part of it.
Common brands: ITW Red Head Drop-In, Hilti HKD, Simpson CNSS
When to Use
- Flush-mount applications where the anchor must be at or below surface level
- Overhead and inverted installations (the bolt threads up into the anchor)
- When a clean finished surface appearance is required
- Light to medium loads in solid, uncracked concrete
Hole Sizing
| Anchor Size | Drill Bit Size | Min. Embedment | Setting Tool Required |
|---|---|---|---|
| 1/4” (1/4-20) | 3/8” | 1” | Yes |
| 3/8” (3/8-16) | 1/2” | 1-3/16” | Yes |
| 1/2” (1/2-13) | 5/8” | 1-7/16” | Yes |
| 5/8” (5/8-11) | 7/8” | 1-3/4” | Yes |
Installation Procedure
- Drill the hole to the required diameter and depth — see table above
- Clean the hole — blow out and vacuum; one pass is sufficient
- Insert the anchor into the hole — the top of the anchor should be flush with or slightly below the concrete surface
- Set the anchor using the correct setting tool and a hammer — strike the setting tool firmly until it bottoms out; the internal cone expands the sleeve outward against the hole wall
- Verify the anchor is set — try to rotate it with needle-nose pliers; it should not move
- Thread in the bolt to the required torque
⚠️ A drop-in anchor that is not properly set is not holding anything. If you skip the setting tool or do not strike it fully, the anchor will pull out under load without warning. Use the correct setting tool for the anchor diameter — they are not interchangeable.
Common Failures
- Skipping or underusing the setting tool — anchor is not expanded and will pull free
- Using the wrong size setting tool — improper expansion
- Drilling oversized holes — sleeve cannot expand enough to grip
Sleeve Anchors
What They Are
A sleeve anchor has a threaded bolt body surrounded by an expanding sleeve. As the nut is tightened, the cone on the bolt draws the sleeve upward and expands it outward. Sleeve anchors are similar in concept to wedge anchors but are generally considered light to medium duty and are more tolerant of varying base materials including hollow block and brick.
Common brands: ITW Red Head Sleeve Anchor, Powers Rawl Sleeve, Simpson Strong-Tie
When to Use
- Light to medium duty mounts in concrete, block, or brick
- When the base material is uncertain or of lower quality
- Retrofit situations where a combination anchor is needed
Hole Sizing
Drill bit diameter equals the anchor outside diameter (same as wedge anchors). Minimum embedment and edge distances follow the same general rules as wedge anchors — confirm with manufacturer specifications for the specific anchor.
Installation Procedure
Similar to wedge anchors: drill to diameter, clean hole, insert through fixture, torque nut. The sleeve will expand as the nut is tightened. Do not over-torque.
Concrete Screws (Tapcon-Style)
What They Are
Concrete screws have hardened, specially-threaded shanks that cut directly into a pre-drilled hole in concrete without any expansion hardware. They are removable and re-installable (with limitations). The ITW Red Head Tapcon is the original product; the name is now used generically across the trade.
When to Use
- Light duty mounts and fixture attachment in concrete, block, or brick
- Temporary or adjustable installations
- Mounting conduit straps, junction boxes, surface raceways, reader backboxes
When NOT to Use
- Heavy structural loads — not appropriate for turnstile or bollard base mounting
- Cracked concrete — the screw threads cannot develop full hold in compromised material
Hole Sizing
Concrete screws require a specific undersized pilot hole to allow the threads to cut into the concrete properly.
| Screw Diameter | Drill Bit Size |
|---|---|
| 3/16” | 5/32” |
| 1/4” | 3/16” |
Installation Procedure
- Drill the pilot hole using an SDS hammer with the correct undersized carbide bit — see table above
- Drill depth = screw embedment depth + 1/2” to allow for dust at the bottom of the hole
- Clean the hole — blow out and vacuum; one pass is sufficient
- Drive the screw using a drill/driver — do not over-torque; the threads are cutting into concrete, not steel; stripped threads cannot be recovered in the same hole
- If a screw strips, move the fixture and drill a new hole — do not attempt to re-use a stripped concrete screw hole with the same size screw
Concrete screws are limited-reuse: each time a concrete screw is removed and redriven into the same hole, it loses holding strength. If an installation is adjusted more than once, use a new hole location or upgrade to a wedge or epoxy anchor.
Anchor Torque Reference
Final installation torque is specified by the anchor manufacturer and varies by diameter, embedment, and concrete strength. Always use the torque value from the specific anchor’s installation data sheet.
General principle:
- Torque is not a clamping force — it is the mechanism that develops expansion in mechanical anchors or the final verification step for epoxy anchors
- Over-torquing can strip threads, crack concrete near the surface, or fracture tile
- Under-torquing leaves mechanical anchors partially expanded and reduces holding strength
For turnstile and access control equipment anchoring, refer to the equipment manufacturer’s installation instructions for the specified anchor size and torque value. When in doubt, confirm with your PM or the manufacturer’s technical support line.
Hole Cleaning Summary
Hole cleanliness directly determines how well an anchor performs.
| Anchor Type | Cleaning Standard |
|---|---|
| Wedge Anchor | One blow-out pass + one vacuum pass |
| Epoxy Anchor | Minimum three blow-out passes + three vacuum passes — do not touch hole after cleaning |
| Drop-In Anchor | One blow-out pass + one vacuum pass |
| Sleeve Anchor | One blow-out pass + one vacuum pass |
| Concrete Screw | One blow-out pass sufficient |
Use a blow-out tube or compressed air nozzle inserted to the bottom of the hole. Always blow toward the opening, not into it.
Last updated: February 21, 2026 Owner: John Lang | jlang@vid-in.com