Mechanical vs. Chemical Anchors
Mechanical and chemical anchors are used for similar purposes, which means that for some jobs, there is debate about where a mechanical or chemical anchor is best. Both types of anchor are used in structural and nonstructural applications, and in some cases, the choice comes down to preference or a coin toss.
In other situations, your choice of anchor could make or break a big building project. For example, some chemical anchors don’t hold up well in seismic conditions while others (usually epoxy or hybrid systems) are a good choice for seismic categories C1 and C2. As they don’t transfer pressure into the substrate they are more suitable than mechanical anchors for use close to edges or in weak or cracked concrete. Plus, as the adhesives used in adhesive anchors have become more sophisticated and they have become more reliable for structural uses, they have been employed more regularly on large jobs.
Let’s take a closer look at the specifics of what mechanical and chemical anchors are used for and how to choose between them.
What Are Mechanical Anchors Used For?
Most post-installation mechanical anchors are used to fasten elements to a main concrete structure or another structural substrate. These elements may be beams, columns, slabs, walkways, and guardrails, among other options.Mechanical anchors usually work by transferring force into the substrate they’re placed in via mechanical interlock or friction. For this reason, the anchors have to be made of very strong materials themselves. Usually, mechanical anchors are steel which is sometimes galvanized or hot dipped, though, for some uses, such as in hollow substrates, they’re made of fiber or plastics. With mechanical anchors, every size, length, and diameter of anchor has a specific load capacity.
Types of Mechanical Anchor
Mechanical anchors can be ‘male’ or ‘female.’ Male anchors extend out of a substrate allowing an element to be fixed to the exposed metal, while female anchors provide a secure hole, often with a thread for elements to be screwed into. All mechanical anchors transfer pressure into the substrate they’re placed in and are designed to be inserted but not removed from a borehole. A few of the most popular types of mechanical anchors are:Wedge Anchors
Wedge anchors are installed using a wrench. Tightening the nut on the exposed end of the anchor once inserted into your pilot/borehole expands a wedge clip at the other end of the anchor.
Sleeve Anchors
Sleeve anchors can be used in a variety of substrates. They consist of a body (the solid metal anchor), an expandable sleeve, a nut, and a washer. The sleeve is inserted into your borehole, and you then add the washer before tightening the nut.
This expands the sleeve so that it pushes reasonably evenly against the walls of the hole.
Hammer Drive Anchors
These two-piece mechanical anchors are an anchor body and an expansion nail. When you hammer the end of the anchor, the nail descends and expands the anchor within your substrate, holding it in place.
Machine Screw Anchors
These female anchors are designed for masonry, concrete, and block. They are made up of a sleeve which is inserted into a guide hole followed by the anchor itself. You then expand the anchor using a setting tool before screwing in whatever element you are attaching.
Double Expansion Anchors
Another female anchor, double expansion anchors, can also be used in brick, block, or concrete. They are made up of two anchor body halves, two expander cones, and a wire. After it has been set into the hole you have drilled in a substrate, you insert a threaded screw or bolt into the bolt. This expands the non-threaded anchor cone to expand and then expands the threaded cone all the way down. The double-expansion system makes it a good choice for weaker substrates, though chemical anchors are often a better choice in a base material of questionable strength.
For chemical anchors, you drill a borehole into your substrate and inject resin into that hole before you push the anchor in. Assuming you properly clean and prepare your borehole, the epoxy or other adhesive will bond completely with both anchor and substrate. Because the adhesive goes in wet, it fills in any inconsistencies or irregularities within the substrate and bonds fully to the anchor itself, including filling in its threads.
This makes the borehole airtight and watertight, meaning chemical anchors are appropriate for adverse weather conditions and industrial settings. Some chemical anchors, specifically epoxy, can even be used underwater.
In chemical anchors, the epoxy or other adhesive is what supports the load put on the anchor. This means that they work in low-psi or cracked concrete and sometimes in other substrates. They also work when placed close to edges or grouped close together.
The main issue with chemical anchors is their installation. Small mistakes, like incorrect angles or poorly cleaned boreholes, can minimize an anchor’s load-bearing capacity as it relies entirely on a full bond between the anchor, adhesive, and substrate.
Weldability And Temperature Resistance
Mechanical anchors aren’t affected by changes in temperature, apart from at incredibly extreme levels. Chemical anchors, on the other hand, can’t stand extreme heat. This makes mechanical anchors weldable and more flexible. They are also more resistant to very low temperatures than adhesive anchors, although this is less of an issue in most cases.
Stability When Tightening
The metal used for most types of anchors is relatively stable when maintaining the force of fastening. With chemical anchors, however, it comes down to your choice of adhesive. Hybrid systems and epoxy acrylic chemical anchors are particularly stable choices, but it’s a job-by-job calculation.
Seismic Performance
Chemical anchors tend to be screw bolts with low strength, and little seismic resistance. Mechanical bolts tend to be stronger and stretch less, so they have more anti-seismic ability.
The Construction Cycle
The curing time of chemical adhesives is 24 hours at an absolute minimum, longer for most adhesives, with time added for low temperatures. This means a longer construction period and potential added cost.
Mechanical anchors, on the other hand, are ready to use as soon as they are installed. This means a shorter construction period.
Ultimately, the type of anchor you choose might come down to the requirements of the engineering or architectural team. Types of anchors for structural uses, particularly when constructing public buildings and utilities, are specified on plans.
Hammer Drive Anchors
These two-piece mechanical anchors are an anchor body and an expansion nail. When you hammer the end of the anchor, the nail descends and expands the anchor within your substrate, holding it in place.
Machine Screw Anchors
These female anchors are designed for masonry, concrete, and block. They are made up of a sleeve which is inserted into a guide hole followed by the anchor itself. You then expand the anchor using a setting tool before screwing in whatever element you are attaching.
Double Expansion Anchors
Another female anchor, double expansion anchors, can also be used in brick, block, or concrete. They are made up of two anchor body halves, two expander cones, and a wire. After it has been set into the hole you have drilled in a substrate, you insert a threaded screw or bolt into the bolt. This expands the non-threaded anchor cone to expand and then expands the threaded cone all the way down. The double-expansion system makes it a good choice for weaker substrates, though chemical anchors are often a better choice in a base material of questionable strength.
What Are Chemical Anchors Used For?
Chemical anchors fulfill many of the same uses as mechanical anchors, but they work via a completely different principle.For chemical anchors, you drill a borehole into your substrate and inject resin into that hole before you push the anchor in. Assuming you properly clean and prepare your borehole, the epoxy or other adhesive will bond completely with both anchor and substrate. Because the adhesive goes in wet, it fills in any inconsistencies or irregularities within the substrate and bonds fully to the anchor itself, including filling in its threads.
This makes the borehole airtight and watertight, meaning chemical anchors are appropriate for adverse weather conditions and industrial settings. Some chemical anchors, specifically epoxy, can even be used underwater.
In chemical anchors, the epoxy or other adhesive is what supports the load put on the anchor. This means that they work in low-psi or cracked concrete and sometimes in other substrates. They also work when placed close to edges or grouped close together.
The main issue with chemical anchors is their installation. Small mistakes, like incorrect angles or poorly cleaned boreholes, can minimize an anchor’s load-bearing capacity as it relies entirely on a full bond between the anchor, adhesive, and substrate.
How to Choose Between Mechanical and Chemical Anchors
Although they seem nominally similar, mechanical and chemical anchors are actually very different. Installation and testing practices vary, and they work on completely different tension and reinforcement principles. A few key ways in which mechanical and chemical anchors differ, which should help you choose between them, include:Weldability And Temperature Resistance
Mechanical anchors aren’t affected by changes in temperature, apart from at incredibly extreme levels. Chemical anchors, on the other hand, can’t stand extreme heat. This makes mechanical anchors weldable and more flexible. They are also more resistant to very low temperatures than adhesive anchors, although this is less of an issue in most cases.
Stability When Tightening
The metal used for most types of anchors is relatively stable when maintaining the force of fastening. With chemical anchors, however, it comes down to your choice of adhesive. Hybrid systems and epoxy acrylic chemical anchors are particularly stable choices, but it’s a job-by-job calculation.
Seismic Performance
Chemical anchors tend to be screw bolts with low strength, and little seismic resistance. Mechanical bolts tend to be stronger and stretch less, so they have more anti-seismic ability.
The Construction Cycle
The curing time of chemical adhesives is 24 hours at an absolute minimum, longer for most adhesives, with time added for low temperatures. This means a longer construction period and potential added cost.
Mechanical anchors, on the other hand, are ready to use as soon as they are installed. This means a shorter construction period.
Ultimately, the type of anchor you choose might come down to the requirements of the engineering or architectural team. Types of anchors for structural uses, particularly when constructing public buildings and utilities, are specified on plans.
Why White Cap?
White Cap supplies everything you need for installing both mechanical and chemical anchors. You can pick up epoxies, anchors, and more in any of our 360+ stores or online. If you need help choosing the right type of anchors, or advice about installing them, you can also reach out to a local White Cap expert.Check out these articles to learn more about Adhesive Anchoring
Factors to Consider When Buying a Caulk Gun
Selecting the Right Caulking Gun Type for Your Project
Maintaining Your Caulking Gun
What are Adhesive Anchors?
Benefits of Chemical Anchors
The Different Types of Adhesive Anchors
Mechanical vs. Chemical Anchors
Determining a Tension Test Load
Infrastructure Applications for Adhesive Anchors
