How Concrete Anchors Work
Concrete fasteners are referred to as expansion type concrete fasteners. They derive their holding values from friction. The friction is obtained by the outward pressure created by expanding the anchor against the walls of the hole that is drilled in the base material. All expansion anchors work on this principle. The only one that does not is the concrete screw. The concrete screw or Tapcon® actually taps or cuts threads into the base material as it is inserted into the hole.
Each type of anchor has a minimum embedment- the minimum distance (in inches) that the anchor must be inserted into the base material for it to obtain its holding values. The deeper the embedment into the base material, the better the holding values. Tapcons have a maximum embedment of 1-3/4". Expansion anchors must be spaced a minimum of 10 anchor diameters away from each other and no closer than 5 anchor diameters from an unsupported edge. Anchors used in outdoor or caustic environments/atmospheres should be stainless steel or zinc plated.
Steps to Installing Concrete Fasteners
To install a concrete anchor, a hole must be drilled in the base material. Carbide tipped drill bits (that meet ANSI standards) must be used as they are tolerance-matched to the concrete fastener. A hammer drill* must also be used because it will drill the hole correctly and is designed to break up the base material as it hammers. The hole should be drilled 1/4" to 1/2" deeper into the base material than the anchor will penetrate. This allows for any material to fall when the anchor is inserted into the hole. After the hole is drilled, it must be cleaned of all debris, material or dust.
* Remember to use safety goggles and earplugs during drilling and to always follow the manufacturers' safety precautions when using power tools.
Wedge Anchor - for use in concrete only
- Drill hole into the concrete using a carbide tipped bit that meets ANSI standards. Bit size = anchor diameter when working with wedge anchors. Drill a hole 1/2" deeper than the anchor will penetrate into the concrete making sure that the minimum embedment requirements are met. The hole can be drilled while the fixture is in place. It is important to make sure that the bit diameter being used will fit through the hole in the fixture.
- Clean out the hole using a wire brush, compressed air, vacuum, blow out bulb or other method.
- Put the nut and washer onto the wedge anchor and make sure that the nut is on the last threads (this will protect the threads from damage when the wedge anchor is hammered into the hole in the concrete).
- Insert the wedge anchor through the fixture's hole and into the hole in the base material. This should be a very tight fit- use a hammer to complete the installation until the nut and washer are tight against the fixture. It is important that the threads go below the surface of either the base material or the fixture.
- Turn the nut clockwise, until finger tight.
- Using a wrench, turn the nut 3-4 times until snug. The recommended torque values can be found here.
Sleeve Anchors - for use in concrete, brick or block
- Using ANSI standard drill bits, carefully drill a hole in the base material. Hole size = Bit size when installing sleeve anchors. Make sure the hole is always drilled 1/2" deeper than the sleeve anchor will penetrate the base material. Minimum embedments also need to be met. The hole can be drilled with the fixture in place making sure the bit will fit through the fixture hole.
- Clean the hole of all debris made during drilling.
- Sleeve anchors come fully assembled with a nut and washer. It is important that the nut is on the end of the threads to protect the threads during hammering.
- Insert the sleeve anchor through the fixture hole and into the hole you drilled in the base material. A hammer will be required to pound the sleeve anchor into the material until the washer and nut are tight against the fixture.
- Tighten nut until finger tight, always turning clockwise.
- Using a wrench, turn 2-4 times until you are sure it is snug.
- The diameter of a drop-in anchor refers to the inside diameter. The hole to be drilled = the same diameter of the outside of the anchor. Carbide tipped drill bits (meeting ANSI standards) must be used. The hole needs to be drilled 1/4" deeper than the anchor will penetrate. The hole can't be drilled while the fixture is in place due to the fact that the hole is larger than the diameter of the bolt being inserted into it. To use a drop in anchor- set the fixture in place, mark where the holes should be drilled, remove the fixture and then drill the holes.
- Clean the hole of any debris before continuing.
- Insert the anchor into the hole. A setting tool is required to set the anchor. Setting tools will correspond to the inside diameter of the drop in anchor. Example: a 3/8" drop in anchor requires a 3/8" setting tool. Setting tool is placed inside the threaded portion of the anchor and struck until the lip of the setting tool touches the lip of the drop in anchor. This will ensure that the anchor is fully set in the concrete.
- Place the fixture over the drop in anchor and thread the bolt through the fixture and into the drop in anchor.
- Anchor diameter = hole size when working with strike anchors. The proper sized carbide drill bit must meet ANSI standards. Hole should be drilled 1/2" deeper to allow space for any dust created during installation.
- Clean the hole of all debris before continuing installation.
- Strike anchor needs to be inserted through the fixture and into the hole with the nut, washer and set-pin in place until the nut and washer are tight against the fixture.
- Using a properly sized hammer for the diameter of the anchor, set the pin with a number of square/sharp strikes to the head of the pin until the pin is flush with the top of the anchor. There is no need to use torque to set the anchor since it is set with the correct set pin.
Lag Shields - for use in concrete, brick or block
- Lag shields are female type anchors. The designated diameter of the anchor = the inside diameter of the lag screw that will be placed into it. Hole size must be larger than the inside diameter. Example: a 3/8" diameter lag shield requires a 5/8" hole. Properly sized ANSI carbide bits must be used to drill the holes for lag shield anchors.
- Clean holes of any debris.
- Place the lag shield in the hole with the closed end of the lag shield inserted first.
- Fixture is then placed over the lag shield, inserting a lag screw through the fixture and into the lag screw. Use a wrench to turn the lag screw clockwise until tight.
All of this information should assist in the safe and correct installation and use of concrete anchors and fasteners no matter what your application may be.
Zinc Plated Wedge Anchors
Hot Dipped Galvanized Wedge Anchors
304 Stainless Steel Wedge Anchors
316 Stainless Steel Wedge Anchors
Zinc Plated Sleeve Anchors
Stainless Steel Sleeve Anchors
Please remember with all fastening jobs to keep safety in mind. Always follow safety instructions on all tools, and refer to manufacturer's installation instructions when available and always remember to wear safety goggles!
Article written by: Bob Carlisle, President Concrete Fastening Systems, Inc