Lag bolts fasten wood or similar material to concrete or masonry. The bolts are a two-part system that utilizes an anchor and bolt to hold tight in hard surfaces such as concrete, blocks or bricks. Installing lag bolts requires some specialized tools and techniques but falls within the capabilities of most do-it-yourselfers.
Creating the Hole
This is the part that requires some specialized equipment. You need a masonry drill to create a hole in the concrete. A masonry or hammer drill along with the masonry drill bit expedite the hole-drilling process. The hole should have the same diameter as the anchor portion of the lag bolt.
Inserting the Anchor
The anchor is the working part of the lag bolt system. The anchor is a soft metal insert that fits within the hole and includes a threaded interior to accept the bolt. The length of the anchor must be long enough to accept the entire length of the bolt. You may need to use a hammer to tap the anchor into the hole.
The bolt passes through the wood object and then connects to the anchor within the concrete. As the bolt enters the anchor it causes expansion of the soft metal of the anchor. This expansion fits the metal tightly within the hole. creating an adhesion. It is the pressure between the anchor and concrete that holds the lag bolt to the concrete.
Lag Bolt Limits
Different size lag bolts are rated for different load limits. Use the proper bolt for the anticipated load of the fixture. Use anchors of corrosion-resistant materials and galvanized bolts if the fixture will be used in moist environments. The size of the lag bolt refers to the exterior diameter of the bolt and the interior diameter of the anchor.
Clean the threads of the anchor bolt of all dirt, debris, rust or concrete. Use a wire brush if necessary.
Hand thread the coupler nut onto the anchor bolt threads. Make sure the top of the nut (the shorter length of the nut above the side indents) will be on the top end of the anchor bolt and not threaded onto the bolt.
Use a wrench to complete tightening the coupler nut onto the anchor bolt threads. Look through the "witness holes" cast in the side of the nut to make sure the threads of the bolt and nut are lining up and interlocking. Remove the nut and re-thread it if the threads are not matching.
Thread the anchor bolt extension into the top of the coupler nut by hand.
Spin the anchor bolt extension nut onto the top of the extension and bring it down all the way to the top of the coupler nut.
Tighten the extension into the coupler nut by gripping the nut on the extension bolt with a wrench and turning it clockwise.
Dig four 12-inch-deep and 10-inch-wide holes where the swing set legs rest so you can insert them into the ground.
Drill two holes at the bottom of each leg with an inward slant so the bolts create an “X” formation when place in the holes. Set one hole about 1/2 inch higher than other so the bolts do not touch each other.
Insert a 12-inch-long galvanized bolt through each hole, so there are two bolts in each swing set leg. Secure the bolts to the legs by sliding on a washer and screwing a nut in place with a wrench.
Set the legs into the holes. Set a level on the swing set to make sure it is leveled before proceeding. Adjust the hole depth to level the swing set, if needed.
Fill one-half of the hole with a quick-setting concrete that you can mix in the hole. Add the appropriate amount of water listed on the package and mix with a stick to combine. Let the concrete cure for four to seven days. Fill the remainder of the hole with dirt and pack it firmly in place with the shovel and stomping the soil with your foot.
Put on your hearing protection and safety glasses.
Select a socket from the socket set that matches the size of the hex nut tightened to the expansion bolt and place the socket onto the 3/8-inch ratchet.
Place the socket onto the expansion bolt hex nut and turn the ratchet handle counterclockwise to loosen the hex nut.
Remove the hex nut from the threads of the expansion bolt.
Secure the expansion bolt extractor into the chuck of the hammer drill. Refer to the operating manual for the hammer drill to determine the proper procedure for securing the expansion bolt extractor.
Fill the hand-pressurized water tank with water and pump the handle of the water tank to pressurize the water.
Slide the expansion bolt extractor over the expansion bolt and press the trigger of the hammer drill to start drilling around the expansion bolt.
Spray water onto the expansion bolt extractor as you drill around the concrete anchor.
Pull the hammer drill toward you to remove the expansion bolt extractor from the concrete.
Remove the loose expansion bolt from the concrete.
Wipe the area around the expansion bolt with clean rags to clean the surface of the concrete.
Refer to local building code about the minimum spacing of anchor bolts. Standard spacing is 3-feet apart, but in areas where earthquakes are common, spacing may be closer. Purchase anchor bolts and have them ready for installation before you pour the foundation walls.
Pour the walls and smooth the top of the concrete with a hand trowel. The top need not be perfectly level in order to insert the anchor bolts.
Push the angled end of an anchor bolt vertically into the wet concrete. The anchor bolt has a straight threaded end with a bend on the other end. The bend goes into the concrete and the threaded end remains out of the concrete.
Leave approximately 1 1/5 inches of the anchor bolt above the level of the concrete. Repeat with each anchor bolt, centering each one in the middle of the concrete, halfway between the sidewall forms.
Insert the anchor bolts quickly to reduce the risk of the concrete hardening before you get them all in.
Tamp the wet concrete around the top of each bolt with a small hand trowel to settle it securely around each bolt and allow the concrete to harden.
J- and L-hook Bolts
J- and L-hook anchor bolts have a bend at one end to grab onto the concrete or masonry structure. These type of anchor bolts are normally cast-in-place---meaning they are inserted into the concrete as soon as it is poured. The concrete cures, and securing retains the bolts in place.
Headed bolts are also cast-in-place anchors. A large head at one end of the bolt holds the anchor bolt in place withing the concrete. The bolts are set in place into wet concrete. The threaded portion of the anchor bolt extends above the surface of the concrete for attaching a washer and nut.
For installation in existing concrete or masonry, wedge-type anchor bolts are used. A hole drilled into the concrete holds the wedge anchor bolt in position. A nut and flat-washer threads onto the opposite end of the bolt. As the nut is tightened, the wedge anchor pulls toward the nut, causing the wedge to spread inside the concrete hole and firmly set itself into place.
Fill every third concrete block with mortar. Insert the fused end of an anchor strap into each filled hole so that the strap will open perpendicular to the wall, i.e, one band opening into the foundation, while the other opens outside the wall. Allow the mortar to harden overnight.
Open the anchor straps so that they form a 180-degree angle atop the wall. Place the first sill plate along the wall, starting at a front corner.
Wrap each strap across the sill plate, and nail through the strap and into the sill with framing nails. Shoot four to six nails into each strap.
Lay the next sill plate end-to-end with the first, and repeat the strapping and nailing procedure. Continue until the the entire wall is covered.