Last updated on October 10, 2021
If you’ve ever tried fixing or mounting stuff on concrete, you’d know that it’s not like putting a candle in a piece of cake. You can’t just simply nail or screw in your fixings just like on wood or metal either.
Concrete is strong when it comes to compression, but has weak tensile strength.
In other words, concrete doesn’t like it when it’s getting pulled apart, which is exactly what happens if you try to directly attach fixings into the holes of concrete.
Thankfully, concrete anchors are here to save you. Let’s take a look at how they work, how many kinds there are, and how and when to use what one.
How do concrete fixings/ anchors work?
Concrete fixings are ribbed or threaded to maximize surface area and tensile strength. They are then set into concrete with a chemical adhesive that hardens when dry.
This applies to cast-in-place concrete anchor bolts.
The threading grips the concrete directly using a square washer and 2 nuts or with a bend instead of a weaker adhesive only join, bending creating a stronger uplift or hold down a bond for heavy structural loads.
Some anchors such as wedge bolts, Trubolts, Dyna bolts expand their tips within a drilled hole, as they get secured in place.
The inner surface of the drilled hole is usually roughened to provide a good grip surface of anchors utilizing mechanical expansion from a plastic plug, or friction-activated glue on power actuated fasteners.
What are the home applications of concrete anchors?
1. Toilet bars and toilet roll holders
Towel racks or bars on concrete-walled bathrooms have to be fixed properly with concrete anchors or they might fall off sooner or later.
2. Wall hangings
Defining features of buildings such as glass curtain walls, wood panels, and metalwork are secured to the concrete skeleton of the building using anchors.
4. Timber to concrete slabs
Structural timber framing is secured to a building’s concrete foundation with concrete anchors attached to sill plates. Here’s a detailed guide to fasten wood and concrete.
5. Metal beams to concrete
Concrete anchors provide mounting points for metal beams (SHS – square hollow section) to be bolted onto a concrete base, or wall.
These anchors help pretty much to secure a floor bike stand on a concrete floor.
6. Wood beams to concrete
Anchors also provide mounting points for pre-drilled structural wood beams on concrete walls.
7. Cinder blocks (masonry blocks)
Anchors are used greatly on the solid portions of cinder blocks to provide reliable mounting for fixtures as long as you get fixing into the concrete inside the block.
Door frames are essential to a doorway’s operation. They are usually made out of wood or metal and are installed on concrete walls using anchors from time to time.
How much weight can concrete anchors hold?
Concrete anchors see frequent use in construction, especially the cast-in-place types. Those are strong enough to secure structural forms such as timber framing to a concrete or masonry foundation.
Post-install bolts, which are installed once the concrete is set, can handle loads of 540-10125 shear lbs depending on the size and type used.
Factors that affect the performance of concrete anchor
Before we discuss the types of concrete anchors, here are some factors that affect how a concrete anchor should hold.
1. Base material
Your concrete anchor may be strong, but the concrete might not be.
It is important to make sure that the concrete base is built properly (High MPA) and is in good condition in order to maximize performance and longevity.
2. Type of material
Anchors are typically made out of either carbon steel or stainless steel. Carbon steel is strong and hard but is prone to rust and corrosion.
That is why they are often zinc-coated to prolong their lifespan. Stainless steel does not have this problem but is generally slightly softer and weaker than the former.
3. Load requirements
It is important to know the load you’re subjecting your anchors to so that they are sized and installed appropriately.
4. Anchor type
There’s a wide selection to choose from and each has its pros and cons and cost. Use the right type for your application to maximize performance. More on this later.
5. Weight capacity/ vertical pressure
The heavier the load, the greater the shear stress exerted on the anchors.
The longer the embedment length, the greater the tensile forces that the concrete anchor can handle.
6. Horizontal force
These are the side-to-side forces along the concrete surface perpendicular to the weight.
The rule of thumb is to set the anchor 3 inches from the unsupported edge to ensure that the concrete will be strong enough to handle the anchor load.
What are cast-in place anchor bolts?
Cast-in-place anchors are types of anchor bolts for concrete that are installed before the concrete sets while it’s still wet . These anchors are the most simple, and the cheapest yet they are the strongest, having high tensile strength and longer embedment lengths with a bend to help stop it from the uplift.
These types of concrete anchor bolts leave their top ends exposed once the concrete is cast, enabling you to mount your fixtures from there.
Their strength is the highest industrial level, but actual numbers are only attained through specific engineering equations.
Although you can only use cast-in anchors on new builds, and will otherwise have to look at the other options for concrete already set.
Types of cast-in-place anchor bolts
1. Plate bolt
The simplest and most common type of cast-in-place anchor bolt, the plate bolt has a smooth shank that is threaded on one end and has a welded plate on the other.
The plate provides bearing resistance, preventing the bolt from pulling out once the concrete is set.
Prepare the concrete forms. Secure the bolt to a holder or guide using a nut and washer at the threaded end. Ensure that the length of exposed threading
2. Threaded rod
A Threaded rod anchor is similar to a plate bolt but its shank is threaded all throughout its length to provide a fixture for a nut and washer later for the hold down on timber.
Using a square washer or a bend in the rod will give more surface area hold down and better engagement with the concrete.
Fasten a plate on one end with nuts, install similarly to a plate bolt, and cast in concrete. Alternatively, it can also be used as a post-install anchor.
For this, drill the appropriately-sized hole and clean using a brush and a blower. Inject concrete adhesive, insert the rod, and let it dry.
Unlike a plate bolt, a J-bolt achieves bearing resistance with a 180-degree bend in place of a welded plate without manually bending. This bend hooks into rebar for extra support.
It is often used for securing walls to concrete foundations and other structural applications.
How to fasten with j-bolts?
To bolt fixings into concrete with J-bolts, first, prepare the concrete forms. Secure the bolt to a holder or guide using a nut and washer at the threaded end. Ensure that the length of exposed threading is sufficient for your application. Place the rod in position and cast in concrete.
As the name suggests, an L-bolt has a 90-degree bend on its lower end. It’s generally lighter-duty than a J-bolt and is commonly used to attach metal plates to concrete or masonry foundations.
Prepare the concrete forms. Secure the bolt to a holder or guide using a nut and washer at the threaded end. Ensure that the length of exposed threading is sufficient for your application. Place the rod in position and cast in concrete.
A pigtail rod might look deformed or crooked but it’s actually what gives it its strength.
The multiple bends on the steel rod provide positive, non-slip anchoring that distributes the load throughout its length.
It’s generally used for lightweight applications such as anchoring plate members.
To install a pigtail anchor:
Prepare the concrete forms. Secure the bolt to a holder or guide using a nut and washer at the threaded end.
Ensure that the length of exposed threading is sufficient for your application. Place the rod in position and cast it in the concrete.
What are post-installed anchor bolts?
Post-installed anchors are anchor bolts that are installed after the concrete base has been set. A hole is then drilled into the concrete which the anchor is later installed in. Here’s a detailed guide on how to use a drill properly.
Post-installed anchors are categorized into two main types: Mechanical Expansion Anchors (MEA) and Adhesive Anchors.
Kinds of post-installed anchor bolts
1. Wedge bolts
Wedge bolts are one-piece heavy-duty anchors with finished hex heads. They’re easy to identify, are vibration-resistant, and are fully removable.
Their threads are self-tapping, giving them a high score when it comes to positive engagement. Use them as fence post fixings to concrete or for shelving, or to install lighting fixtures on concrete.
How to install wedge bolts?
Select the properly sized wedge-bit and drill a hole roughly ½” deeper than the required embedment.
Insert the anchor through the fixture and into the hole. Turn clockwise to tighten or use an impact wrench.
Tru bolts are true-to-size heavy-duty anchors that are torque controlled and rely primarily on expansion to serve as a permanent concrete anchoring option.
Anti-rotation expansion sleeves are designed to grip the sides of holes to prevent anchor rotation during installation.
Better suited for certain structural safety applications such as installation of rails, balustrades, and columns/beams and as a stronger hold for outdoor or tanalized wood framing to concrete over Dyna bolts (As you get Trubolts galvanized).
When installing Trubolts:
Drill the appropriately sized hole with the help of a fixture template.
Insert the anchor through the fixture and drive it down with a hammer until the washer contacts the fixture. Tighten with an impact or torque wrench.
Here are more hammer types for different jobs.
3. Dyna bolts
Dyna bolts are often used to anchor wood and steel fixtures onto concrete-like bottom plates in wall frames and for mounting hardware to walls.
It’s also an expansion anchor with an integrated pull-down section, allowing for better grip and engagement more suited for medium-duty anchoring.
A versatile anchor choice for different applications. And can be removed later with a hole punch, unlike Trubolts.
Drill the appropriately sized hole with the help of a fixture template. Insert the anchor through the fixture and drive it down with a hammer until the washer contacts the fixture.
Tighten with a torque wrench and allow the sleeve to twist and pull down the fixture onto the substrate.
4. Strike anchor bolts
Strike anchors are lightweight non-structural concrete fasteners.
They’re specifically designed and are often made up of a body and a drive pin and are not compatible with any other masonry type.
Installing strike anchor bolts:
Plan and drill the correctly sized hole. Allow at least a ½” excess hole depth. Clean the hole and place the washer over the anchor’s threaded end.
Place the nut on the threaded end and turn clockwise until it lies flush with the body.
Insert through the hole and drive with a hammer until the nut is tight against the surface. Insert through the fixture and into the concrete.
5. Lag shield
Lag shields are screw-style anchors designed to work with lag bolts across a variety of masonry materials.
There are long and short style lag shields, the latter makes drilling harder materials quicker, while the former is used to strengthen weaker/softer masonry materials.
Mainly sees actions in mortar joints of block and brick walls.
How to use a lag shield?
Drill an appropriate-sized hole. Clean the hole. Insert the anchor and tap using a hammer, ensure that it lies flush against the base material.
Insert the fixture over the anchor then insert the correctly-sized lag bolt. Tighten and secure.
6. Leadwood screw
A fastener ideal for use with blocks, bricks, and concrete.
Like strike anchors, these concrete screw fixings are mainly for use with lighter applications such as bike racks and wall and ceiling mounts supporting 50lbs load or less.
Using a leadwood screw:
Drill a hole in the base material and with an excess depth about ⅛” more than the anchor length for flush mounting.
Insert the anchor into the hole and tap lightly with a hammer. Set the fixture over the anchor and use the appropriate screw to secure it in place.
7. Double expansion
Double expansion anchors come into play when anchoring on uncertain material.
While most concrete anchors rely on the deformation of the lower end of the fastener, double expansion anchors are designed in such a way that the entire anchor expands.
These anchors are best used to support heavy and even structural load on softer masonry material such as brick.
How to install double expansion anchors?
Suggested you use a correctly-sized SDS drill bit. Leave a small excess about ½” longer than the anchor’s length. Clean the hole and insert the anchor’s threaded portion near the bottom.
Drill a hole in the material to be anchored and line up the screw holes as well as use a machine screw to catch its threads.
Tighten with a screwdriver until the machine screw tightens against the surface.
8. Hurricane shutter bolts
Hurricane shutter anchors or hurricane fasteners are primarily structural fasteners that are designed to fasten hurricane insert into different masonry types.
They come in two lengths, with the shorter one being the one for direct use with concrete bases. Commonly used when installing hurricane panels and other fixtures for storm protection.
Fastening with hurricane shutter bolts:
Drill a hole in the base material and with the standard excess. Clean the hole. Insert the anchor with the threaded end facing the hole. Drive it in using the stepping tool and a hammer.
9. Split-drive anchor bolts
Split drive anchors are usually one-piece expansion anchors used for attaching plywood sheets to concrete subfloors. They’re designed for use with solid masonry types, mainly the likes of concrete, and are permanent and tamper-proof once in place.
Installing split-drive anchors:
Drill a hole along with the standard excess. Clean the hole and line up the fixture.
Insert the anchor and drive it through. Once inside, the two pre-expanded halves attempt to regain their original shape, thus allowing themselves to set via friction.
10. Ramset pins with washers
The standard Ramset drive pins have one head diameter, but different lengths. The powder-actuated fastener is mainly used to directly affix objects to hard and incredibly dense material.
How to use ramset pins with washers?
They work pretty much like nail guns. Once you have your layout, line up the Ramset tool and hold it at 90-degrees.
Firmly push down on the tool to cock it, then pull the trigger to fire and drive the concrete faster in. Maintain minimum edge spacing of about 3 inches.
How to hold timber firmly in place?
Without having to use clamps and vises, you can often hold timber for anchoring with your hands or by using Powder Actuated Tools (PATs) such as those made famous by Ramset and Hilti.
As mentioned in the previous paragraph, PATs are pretty much-overpowered nail guns, making use of firing pins and small explosive cartridges to seamlessly drive anchors through hard and dense surfaces like steel and concrete.
It limits the structural damage while fully allowing the fasteners to set.
Though they don’t have as high a shear strength as other anchors, they’re perfect for framing and attaching wood panels/sheets to concrete walls and floors to hold them steady for a structural anchor.
What tools are needed for working with concrete anchors?
1. Impact wrench
Impact wrenches are a regular staple when it comes to installing anchors.
Though not all anchors would require an impact wrench to install, especially torque-sensitive ones are impossible to affix without one.
If you mainly work with heavy-duty anchors, like Tru and Dyna bolts, then it’s best to have one of these around.
But be very careful to set the tool from over-tightening, for this reason, many builders prefer to do it by hand to make sure the anchor is correctly gripped.
To find out what more it does and how it’s different from an impact driver, check this out.
Anchor installation kits, such as Apex’s Crescent setting tool set/s, are handy universal tools for when you need to work with various anchors all while only using one kit.
Alternatively, the crescent or adjustable wrench is also a versatile manual torquing tool for tightening or loosening nuts and bolts.
3. Impact sockets
Nothing works better with impact tools than these. Impact sockets function the same way regular sockets do, only that they are hardened so as to better resist vibration.
Impact sockets improve impact tool safety and help prolong longevity by dissipating impact damage to the tool’s anvil.
Check these 3/8 inch impact socket sets for your convenience.
4. Dyna drill
Also called combi hammers, these distinct rotary tools are best used for straight and directional drilling.
Typically larger than other handheld power drills, Dyna drills are more efficient when needing to drill thicker and harder material, making them perfect as hole-makers for anchors.
5. Brushes and blowers
These tools are necessary when using adhesive anchors to make sure the glue fastens to the surrounding concrete and not just dust.
You use brushes to clean your drilled holes first and then a blower before inserting any anchors that will be glued into place.
The nozzle on the end of the blower needs to be long enough to go inside the concrete hole and to hit the bottom of the hole.
So that the air pressure blows the thick dust upwards, not downwards. Other than a standard hand-powered concrete blower you can use a corded or cordless blower by taping on a thinner nozzle onto the end.
6. Epoxy glue gun
You would need to use an epoxy glue gun, for adhesive anchors to mix the two-part epoxy from the cartridge.
Epoxy glue functions as a sealant and helps give a stronger than concrete bond to support connections.
Especially when anchoring on concrete surfaces near or within marine compounds, using epoxy glue helps give an additional layer of protection to the metallic anchors.
Tips for safe installation of bolts
- Always refer to specific installation guidelines/instructions (if included).
- Remember to drill holes that correctly correspond to the size of the anchors you’ll be using.
- Always leave an excess of about ½” more than the length of the anchor as embedment.
- Duly clean holes before inserting anchors. This’ll help anchors achieve a better and more lasting hold. And is essential for adhesive anchors.
- Mind the torque. Especially if you’ll be using impact tools, be sure to not apply too much as over-torquing can potentially damage and break sockets, as well as the anchors, hold themselves.
There are a lot of anchors to choose from. Even as fasteners, these rods still have classifications that range from light to heavy-duty, indicating that specific applications will need you to use specific anchors, lest there be catastrophic failures.
Depending on what you need to be anchored, always keep in mind that your anchors of choice should be up to the task.
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