Photo: Anete Lusina

What size anchors for 2x4 concrete?

As a rule of thumb, the space for the nut and washer is equal to the diameter of the wedge anchor being used. For example, if a 2x4 is being fastened to concrete with a 1/2” wedge anchor then the minimum length of wedge anchor would be 1-1/2”(2x4) + 2-1/4”(minimum embedment) + 1/2”(space for nut and washer) = 4-1/4”.

concretefasteners.com - Wedge Anchor Lengths - Concrete Fasteners

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Purchase Anchors

Many times wedge anchors are purchased in longer lengths to allow for deeper installation into the concrete, since the deeper the embedment into the concrete then the stronger the holding power will be. That concept might be theoretically correct but it is a misunderstanding that may be wrong in many cases and when taken to an extreme.

Lengths of Wedge Anchor

Each diameter of wedge anchors comes in different lengths to accommodate different thickness of material to be fastened. Each diameter of wedge anchor must be embedded into the concrete a minimum distance for the wedge anchor to reach minimum holding values. This means that the body of the wedge anchor must be embedded in the concrete the minimum distance after it has been set, and the correct torque value applied. Diameter of Wedge Anchor Minimum Embedment Depth 1/4” 1-1/8” 5/16” 1-1/4” 3/8” 1-1/2” 1/2” 2-1/4 5/8” 2-3/4” 3/4” 3-1/4” 7/8” 3-7/8” 1” 4-1/2” 1-1/4” 5-1/2” Wedge anchors can be installed deeper in the concrete than the minimum embedment depth and will provide better holding values as long as the depth of embedment is not taken to extremes.

Extreme Embedments

Various problems can arise when trying to embed a wedge anchor at deep embedments into the concrete: Many times rebar is buried in the concrete. Once the rebar is run into during the drilling process then the longer length wedge anchor may not be able to be used. The threads do not go below the surface, and therefore will not allow the wedge anchor to be set. One solution is to use fully threaded wedge anchors. They can be used in this situation, but extreme caution must be taken. Fully threaded wedge anchors are designed so that they can be installed at embedments less than minimum embedment depth. Make sure that the hole is deep enough to allow for the minimum embedment of the wedge anchor. Extreme embedments such as a 1/2” diameter by 10” long wedge anchor to attach a 1” thick fixture to concrete will give an embedment depth of 8-1/2” and allow 1/2” for the nut and washer. A hole depth of 9” is drilled into the concrete, and the wedge anchor is inserted into the hole and pounded in. As the wedge anchor is pounded in, it may stop at some point. Continued hammering may result in beending the wedge anchor, and it will become very difficult to drill a perfectly straight hole in the concrete to these depths. It is very difficult to consistently drill a deep hole in concrete to allow the wedge anchor to match up and be able to be inserted for the entire length of the hole. The wedge anchor is straight and the slightest change in hole direction will cause the wedge anchor to contact the concrete on the side of the hole. This will disable the wedge anchor from being inserted any further into the hole.

Minimum Length of Wedge Anchor

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The minimum length of wedge anchor to use is determined by adding the thickness of the material being fastened plus the minimum embedment for the diameter of wedge anchor being used plus space for the nut and washer. As a rule of thumb, the space for the nut and washer is equal to the diameter of the wedge anchor being used. For example, if a 2x4 is being fastened to concrete with a 1/2” wedge anchor then the minimum length of wedge anchor would be 1-1/2”(2x4) + 2-1/4”(minimum embedment) + 1/2”(space for nut and washer) = 4-1/4”. The minimum length of 1/2” diameter wedge anchor to use for this application would be 4-1/4”.

FT + ME + NW = MLWA

FT = fixture thickness ME = minimum embedment NW= thickness of nut & washer MLWA = minimum length wedge anchor

Installation

Watch the video and follow the steps below to ensure a quality wedge anchor installation.

VIDEO

Installation Steps

Drill a hole in the concrete using a hammer drill in the hammer mode and using carbide tipped drill bit that meets ANSI standard B212.15 and which is the same diameter as the diameter of the wedge anchor being installed. Drill the depth of the hole a minimum of 1/2” deeper than the minimum depth of embedment. Using a wire brush, compressed air or vacuum, clean the hole of all debris and dust. Thread nut onto the threaded end of wedge anchor. The top of the nut must be flush with the top of the wedge anchor to protect the threads from damage during installation. Insert wedge anchor, clipped end first, into the predrilled hole in the concrete. If the wedge anchor is being installed through a hole in a fixture, make sure that the hole diameter is larger than the diameter of the wedge anchor being used. With a hammer, strike the nutted end of the wedge anchor until a minimum of 6 threads are below the surface of the concrete or the surface of the item being attached. Using your fingers, tighten the nut. Take a wrench and turn the nut clockwise 2 to 3 turns or until the proper torque values for the diameter of wedge anchor being used is obtained.

Fixture Hole

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The wedge anchor diameter is larger than the designated diameter.

If the wedge anchor is to be inserted through the hole in the fixture, the hole in the fixture must be larger than the designated diameter of the wedge anchor. Diameter Wedge Anchor Fixture Hole 1/4” 5/16” 5/16” 3/8” 3/8” 1/2” 1/2” 5/8” 5/8” 3/4” 3/4” 7/8” 7/8” 1” 1” 1-1/4” 1-1/4” 1-3/8”

Torque Value

Each diameter of wedge anchor needs to be torqued within a range to ensure proper expansion. Wedge Anchor Diameter Torque Value Ft/lbs. 1/4” 5-10 5/16” 5-10 3/8” 25-30 1/2” 50-60 5/8” 75-90 3/4” 150-175 7/8” 200-250 1” 250-300 1-1/4” 400-450