A double expansion anchor is a type of masonry anchor used for anchoring into materials of questionable strength or quality. In the world of masonry anchors, most rely on deforming a portion near the bottom of the anchor once inside a hole to prevent the anchor from coming loose.
Double expansion anchors differ from other masonry anchors. Instead of the bottom portion of the anchor expanding dramatically to create a strong grip, the entire anchor expands, but only slightly, in size to distribute the pressure over the entire surface area of the anchor.
When Do You Use One?
Basically, most masonry anchors are one way entry devices; they’re not meant to come out. In large slabs of concrete, most of these anchors work fine because the concrete is so strong that the anchors can place a large amount of force against it without risk of damaging the concrete. This becomes a problem with certain masonry materials.
Brick is a perfect example of a softer small masonry material. Due to its size and shape, brick can be considered delicate. Common expansion anchors placed in brick will almost certainly crack or damage the brick.
A double expansion anchor would be used when the material being installed in is of a weak material or of questionable quality. They expand evenly and distribute their holding power over the entire hole. This minimal expansion over a much wider surface area still provides a strong holding power that does not damage the brick.
Installing A Double Expansion Anchor
To install a double expansion anchor, follow the steps below:
Using an SDS drill bit, drill a hole into the brick the same diameter as the anchor. The hole will need to be slightly longer than the anchor in-depth.
After cleaning out and debris from the hole, insert the double expansion anchor into the hole with the threaded portion near the bottom.
Next drill a hole through the material that will be anchored to the brick.
Line up the holes and use a matching machine screw to catch the threads of the anchor. The initial spins can be done by hand.
Using a screwdriver, tighten the machine screw until it tightens against the surface of the material being connected to the brick. *Note: The length of the machine screw will vary depending on what you are attaching to the brick.
One of the unique things about double expansion anchors is that they can be easily removed from an installation hole and reused. To remove one simply take out the machine screw and it will form back into its original shape. Then it can be removed from the hole.
There are many types of masonry anchors available today. The problem for many is determining which of these anchors they need to perform the job. Listed below are some of the more common fasteners found in the masonry field.
Drop In Anchors
A Masonry Drop In Anchor is mostly used in poured concrete. They are used in high strength applications by fastening a bolt into the internal threading of the anchor. They are also available in coil threading (a coarser thread for coil threaded rod). Some masonry anchors have a lip to prevent the anchor from dropping too far into the concrete.
To install the drop in anchor, drill a hole the same diameter as the anchor and only as deep as the anchor itself. Then drop the anchor into the hole and seat the setting tool inside of it. Then hit the setting tool with a hammer. The bottom portion of the anchor will deform resulting in a wedged anchor that cannot be removed.
Lag Shield Anchors
A Lag Shield Concrete Anchor is used in combination with a lag screw to create an anchor in concrete. Lag shields are made of two parts and when the lag screw is driven into the shield, it expands resulting in a tight wedge in the concrete.
Lag Shield Anchors are very similar to a drop in anchor but are designed specifically to take a lag screw. Lag screw anchors also do not require a setting tool to install.
Masonry Concrete Screws
Masonry Concrete Screws, sometimes referred to as Tapcons, are probably the most common concrete fastener used. Concrete screws are easy to identify based on their bright blue coating. They are used for fastening wood or metal to different masonry materials. They are available in both Phillips flat head (for flush finishes) and hex head (for ease of installation).
Installing a concrete screw is very simple. First, drill a hole through both materials and then simply drive the screw into the hole. Make sure you use a screw that is long enough to reach through both materials otherwise you will not have a firm hold.
Sammys Hanging Anchors
Sammys Screws are a common anchor used for hanging applications. Most often installed vertically or horizontally, these anchors have a threaded opening used to receive threaded rod. Sammys are commonly used in HVAC applications for hanging duct. The term Sammys, much like Tapcon, is a brand name. There are many types of these hanging anchors available.
To install a Sammys screw, first drill a hole into the material and use a wrench or socket to drive the anchor into the material. Once installed to the silver head, remove the wrench and screw in a piece of threaded rod.
Hammer Driven Pin Anchor
A Hammer Driven Pin Anchor is a small anchor which is mostly used to fasten plywood to concrete. These anchors are very simple to use. They have a lip over the head making it compatible with holes that may have accidentally been driven too far into the material.
To install one of these pin anchors, drill a hole through both materials and drop the anchor into the hole. Once the lip is seated against the top of the material, hit the exposed pin with a hammer. The pin is driven down through the middle of the fastener pushing both sides out in a wedge fashion holding the fastener in place.
Toggle Wing Anchors
A Toggle Wing Anchor is used when a hollow wall is present. This is common when cinder blocks are used to create the walls of a building. They are also commonly used in drywall applications. It is not recommended to use heavy weight on these anchors especially in drywall as they will rip through the material.
To install one of these anchors, first a hole must be drilled big enough for the toggle portion of the anchor to push though. Once in the hollow part of the wall, the toggle wing will expand. Then using either a Phillips or Slotted head screwdriver, the bolt is driven into the toggle wing pulling it against the other side of the wall. This allows the bolt to tighten down on the material being hung.
Double Expansion Shield Anchor
Double Expansion Shield Anchors are used primarily used in brick and block. As a screw is driven into the anchor, it starts to pull down towards the middle resulting in an expanded anchor. These anchors only expand so much. The reason for this is to prevent brick from cracking.
To install a double expansion shield anchor, simply drill a hole large enough for the anchor to drop into and then install the screw into the anchor. As you fasten the screw it will pull the bottom towards the middle and force the top down to the middle as well. The result it a limited but effective amount of expansion on the anchor. The limit of expansion highly reduces the chance of cracking brick or block.
Sleeve anchors are fairly simple to use and are primarily used in brick or block. They can be used in concrete but are not considered as strong as a wedge anchor. So, for light to medium holding applications, a sleeve anchor is a good choice. There are two common types of sleeve anchors. They are the Nut Drive which is commonly used for extra strength and Phillips/Slotted Combo Driven Flat Head which is used when a flush surface is required.
To install the nut driven style, drill a hole and place the sleeve anchor into the hole. Then place the washer and nut onto the exposed threading and begin fastening the nut. As the anchor is pulled up out of the concrete, the sleeve around it begins to expand wedging the anchor into place inside the hole. You can install the Combo Flat head style in much the same way except you are using a Phillips drive and the installation will leave the top flush with the surface of the installation material.
Wedge Anchors are extremely popular and are one of the strongest anchors for hold strength. Wedge anchors look and function like a sleeve anchor but have a much smaller sleeve near the bottom of the anchor.
To install a wedge anchor simply drill a hole that is the same size diameter as the anchor and place it into the hole. After placing the material being held to the concrete on the exposed portion, place the washer and thread the fastener onto the anchor. As the nut is tightened against the washer, it will begin pulling the anchor up. This will result in the wedge skirt catching the concrete and expanding and digging into the concrete as the anchor is pulled.