Mechanical vs Chemical Anchors – Which Should You Choose?
Mechanical and chemical anchors are both widely used for fixing steel components to concrete, but they transfer loads in different ways and have different installation requirements.
The right choice depends on the complete application: the loads, concrete condition, available edge distances and spacing, installation environment, required embedment and product approval. Neither anchoring method is automatically better than the other.
Understanding the differences helps engineers, buyers and installers select a fixing system that is suitable for both the design requirements and the conditions on site.
Mechanical vs chemical anchors – the key difference
The fundamental difference is how the anchoring system transfers load into the concrete.
Mechanical anchors
Transfer loads through mechanical action such as expansion, undercutting or interlock between the anchor and the surrounding concrete.
Chemical anchors
Use a resin or bonding material to transfer loads between a threaded anchor element or reinforcing bar and the wall of the prepared drill hole.
This difference affects installation speed, curing requirements, hole preparation, sensitivity to installation conditions and the way each system can be used within the geometry of the connection.
How mechanical anchors work
Mechanical anchors develop their connection with the concrete through a physical mechanical action.
Depending on the anchor design, this can include:
- Expansion against the wall of the drill hole
- Mechanical interlock
- Undercutting within the concrete
- Thread engagement, as used by concrete screws
For expansion anchors, tightening can cause part of the anchor to expand against the surrounding concrete. The installation torque, embedment depth, spacing and edge distance specified for the particular product are therefore important.
Suitable mechanical anchors can provide a fast and efficient installation route and, depending on the product, may be capable of carrying load immediately after correct installation.
How chemical anchors work
Chemical anchors, also known as bonded or resin anchors, use a bonding material to secure a threaded element or reinforcing bar inside a drilled hole.
The resin fills the space between the anchor element and the drill-hole wall, allowing forces to be transferred into the surrounding base material after the system has cured.
Performance depends on correct installation, including:
- Drill-hole diameter and depth
- Specified hole-cleaning procedure
- Correct preparation and dispensing of the resin
- Anchor insertion
- Base-material temperature
- Required curing time
The anchorage should not be loaded until the curing requirements for the specific product and installation temperature have been satisfied.
Mechanical and chemical anchors at a glance
Mechanical anchors
- Mechanical load transfer
- Often fast to install
- Immediate loading may be possible for suitable products
- No resin curing period
- Installation torque may be critical for some anchor types
- Expansion forces may need to be considered
Chemical anchors
- Bonded load transfer using resin
- Requires controlled hole preparation
- Must cure before loading
- Curing time is temperature dependent
- Can offer flexibility in embedment and connection design where approved
- No installation expansion force from tightening the anchor
When mechanical anchors may be suitable
Mechanical anchors can be particularly attractive where installation speed and a straightforward fixing process are important.
Depending on the specific product and approval, they may be suitable where:
- Rapid installation is required
- Immediate loading is beneficial
- A defined mechanical fixing method is preferred
- Site conditions are suitable for the required drilling and setting procedure
- The available edge distances and spacing meet the design requirements
Typical applications can include steel base plates, brackets, support frames, handrails and secondary steelwork.
Mechanical anchors should always be selected according to the actual load case, concrete condition and scope of their technical approval.
When chemical anchors may be suitable
Chemical anchoring systems can provide useful design flexibility where bonded installation is appropriate for the connection.
Depending on the specific system and approval, they may be considered where:
- Reduced installation expansion forces are advantageous
- A threaded rod or reinforcing-bar solution is required
- Different approved embedment depths provide design flexibility
- The connection geometry makes a bonded solution attractive
- The installation and curing process can be controlled correctly
Chemical anchors are not automatically suitable simply because space is restricted. Edge distances, spacing, embedment and member thickness still need to satisfy the applicable design and product requirements.
Expansion forces, edge distance and anchor spacing
Some mechanical expansion anchors generate forces against the wall of the drill hole during installation. This can influence how close the fixing can be positioned to a concrete edge or another anchor.
Bonded anchors do not create the same installation expansion action, which can make them useful in some restricted geometries. However, this does not mean that chemical anchors can be installed at any edge distance or spacing.
Both systems transfer design loads into the surrounding concrete, and the applicable edge distances and anchor spacing must be assessed for the specific anchoring system and connection.
Explore edge distance, spacing and embedment requirements >
Installation speed and loadability
Installation time can be an important practical difference between the two systems.
Mechanical anchors
Many mechanical anchors can be installed, set and made ready for use in a relatively short process. Where permitted by the product documentation, loading can often take place immediately after correct installation.
Chemical anchors
Chemical anchors require the resin to cure before the anchorage can be loaded. The required curing period depends on the particular resin system and installation temperature.
This additional time should be considered when planning site activities, particularly where installation is taking place in colder conditions.
Drill-hole preparation
Correct drill-hole preparation matters for every anchoring system, but it is particularly critical for bonded anchors.
Residual drilling dust can interfere with the bond between the resin and the concrete. Depending on the selected product, the specified procedure may involve blowing, brushing, vacuum cleaning or another approved cleaning method.
The exact sequence must follow the installation instructions for the individual anchoring system.
Mechanical anchors also rely on a correctly sized and prepared drill hole, so specified drill diameter, depth and installation procedure should not be treated as optional.
Explore anchor installation and mounting methods >
Cracked and non-cracked concrete
Both mechanical and chemical anchoring systems can be available for cracked or non-cracked concrete, but suitability depends on the individual product and its approval.
An anchor should not be assumed to be suitable for cracked concrete simply because it is described as a mechanical or chemical anchor.
Where cracking can occur at the anchor position, the relevant technical documentation should confirm that the selected system is suitable for those conditions.
Approval for cracked concrete should also not automatically be interpreted as approval for seismic applications.
Understand cracked and non-cracked concrete >
Loads and embedment depth
The choice between mechanical and chemical anchoring should not be made from anchor type alone. The actual tension, shear and combined loads need to be considered alongside the available connection geometry.
Embedment depth also influences how forces are transferred into the concrete. Some anchoring systems provide more than one approved embedment option, while others have defined installation depths for the particular anchor size.
The selected embedment must remain within the conditions covered by the product documentation and structural design.
Explore tension, shear and combined anchor loads >
Temperature and site conditions
Site conditions can influence which anchoring route is most practical.
Chemical anchoring systems are particularly sensitive to temperature during installation because temperature can influence resin handling and curing time. The approved installation-temperature range and curing schedule should therefore be checked before work starts.
Mechanical anchors do not require resin curing, but the specified installation conditions, drill-hole preparation and setting procedure still need to be followed.
For either system, wet holes, overhead installation or other unusual site conditions should only be accepted where they fall within the stated conditions for the specific product.
Corrosion and environmental exposure
Whether the anchor is mechanical or chemical does not by itself determine its suitability for the service environment.
The material and corrosion resistance of the anchor element should be appropriate for factors including:
- Indoor or outdoor exposure
- Humidity and condensation
- Direct weather exposure
- Industrial environments
- Marine or chloride exposure
- Required service life
For chemical systems, the suitability of the complete approved system, including the anchor element and resin, should be considered.
ETA and approval requirements
Anchor type alone does not demonstrate that a product is suitable for a structural application.
The relevant European Technical Assessment (ETA) provides product-specific information about the conditions under which an anchoring system has been assessed.
Depending on the product, this can include:
- Approved concrete strength classes
- Cracked or non-cracked concrete
- Anchor dimensions
- Embedment depths
- Edge distances and spacing
- Installation conditions
- Temperature ranges
- Fire or seismic performance where assessed
The ETA and associated product information should be checked against the actual application rather than treating the existence of an ETA as a general approval for every use.
Learn more about ETA and DoP documentation >
How to choose between mechanical and chemical anchors
A useful selection process is to compare both options against the same application requirements.
Ask:
- What tension and shear loads need to be transferred?
- Is the concrete cracked or non-cracked?
- What edge distances and anchor spacing are available?
- What embedment depth can be achieved?
- How thick is the concrete member?
- How quickly must the fixing be loaded?
- Can resin curing conditions be controlled on site?
- What environmental exposure will the connection experience?
- Are fire or seismic requirements applicable?
- Does the relevant ETA cover the intended application?
The best solution is the one that satisfies the structural, installation and documentation requirements of the complete connection.
Calculate mechanical and chemical anchor solutions
Where a structural post-installed anchorage in concrete needs to be designed, comparing products from individual catalogue load values is not sufficient.
The Fabory Anchor Calculator helps designers evaluate post-installed anchors for structural use in concrete in accordance with EN 1992-4.
Enter the application parameters to assess suitable solutions based on:
- Tension and shear loads
- Combined loading
- Cracked or non-cracked concrete
- Anchor position and configuration
- Edge distances
- Anchor spacing
- Embedment conditions
- Fire and seismic requirements where applicable
The calculator can indicate which available anchors satisfy the entered structural requirements and why other solutions are rejected.
Use the Fabory Anchor Calculator >
Explore mechanical and chemical anchors
Mechanical anchors
Explore heavy-duty mechanical anchoring products for concrete fixing applications.
Chemical anchors
Explore chemical and bonded anchoring systems for suitable concrete applications.
Common anchor selection mistakes
Some of the most common problems occur when mechanical or chemical anchors are chosen on one characteristic alone.
- Assuming mechanical anchors are always faster without checking the full installation
- Assuming chemical anchors can always be installed closer to an edge
- Choosing an anchor from a single published load value
- Ignoring cracked-concrete requirements
- Not checking curing temperature and time for chemical anchors
- Failing to follow the specified drill-hole preparation procedure
- Using a product outside the conditions covered by its approval
Explore more anchoring guidance
Continue exploring the technical factors that influence anchor selection and design:
- Steel-to-concrete anchoring >
- Types of anchors >
- Understanding anchor loads >
- Anchoring base materials >
- Cracked and non-cracked concrete >
- Anchoring conditions >
- Anchor installation and mounting methods >
- Practical anchor design >
Need help choosing between mechanical and chemical anchors?
The best anchoring method depends on the actual load case, concrete condition, geometry, installation environment and documentation requirements.
Fabory's specialists can help you assess the application and identify suitable mechanical or chemical anchoring options.
Frequently asked questions about mechanical and chemical anchors
Find answers to common questions about choosing between mechanical and chemical anchoring systems.
What is the difference between a mechanical anchor and a chemical anchor?
Mechanical anchors transfer load through a mechanical action such as expansion, interlock or undercutting within the concrete. Chemical anchors use a resin or bonding material to transfer loads between an anchor element and the prepared drill hole.
Are chemical anchors stronger than mechanical anchors?
Not necessarily. The resistance of either system depends on the individual product, anchor size, embedment, concrete condition, connection geometry and applied loads. The appropriate anchoring system should be selected from the complete application rather than anchor type alone.
Can chemical anchors be installed closer to a concrete edge?
Bonded anchors do not create the same installation expansion action as expansion anchors, which can be advantageous in some restricted geometries. However, chemical anchors still have defined edge-distance and spacing requirements that must be checked for the specific system and structural design.
Can mechanical anchors be loaded immediately?
Many mechanical anchors can be loaded after correct installation without waiting for a curing period, but this depends on the specific anchoring system and its installation requirements. The relevant product documentation should always be followed.
How long does a chemical anchor need to cure?
Curing time depends on the particular resin system and the temperature of the base material. The curing period specified in the product installation instructions should be completed before the anchorage is loaded.
Can the Fabory Anchor Calculator help compare anchoring solutions?
Yes. The Fabory Anchor Calculator assesses available post-installed anchors for structural use in concrete against the entered loads, concrete conditions and connection geometry in accordance with EN 1992-4.