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For applications that require fastening to concrete blocks, it is important to gather information in advance; this will help inform decisions about where to drill into the block and the best anchor choice for the specific application.

The decision of anchor placement in the block depends if the fastener will be placed in the:

Some applications may allow each fastener to be placed in the same part of the block, while other installations require that each anchor be placed in different sections of the block.

Tip: All anchors - except for concrete screws - exert an outward force. An anchor exerting this pressure against an unsupported edge decreases the anchor’s holding values.

Fastening into the mortar joint can be an excellent option depending on the quality and quantity of mortar used to set the block in place. The block’s solid sections usually offer the best quality fastening; this will depend on the distance of the fastener to the unsupported edge of the cavity and the quality of the material from which the block is made.

The hollow section of the block is the least desirable section in which to fasten, but this is sometimes unavoidable. When fastening into the hollow section of a block, there are a few important considerations to keep in mind:

The next step in the process is to ascertain the type of load that is going to be anchored:

Finally, it’s time to determine the appropriate type of fastener for the application. There are four options for use in concrete block:

If using a stud-type anchor, female type anchor, or the concrete screw, then the item being fastened can be removed at any time with little or no damage to the concrete block. However, hammer-type anchors are permanent installations. Removing these fasteners will greatly damage the concrete block and possibly the fixture as well.

Sleeve anchors come in the widest variety of sizes for applications that fall into this category.

Anchors with diameters ranging from 1/4" to 5/16" are sufficient for most light duty applications while the 3/8" and 1/2" diameters are adequate for most medium duty situations. Sleeve anchors with diameters of 5/8" and 3/4" are usually considered heavy duty anchors. An engineer should be consulted every time concrete anchors are used for heavy loads.

Because of the variety of lengths available, this anchor type is extremely versatile and can be used to attach materials of many different thicknesses to a block wall. The sleeve anchor also comes in a variety of head styles for varying aesthetics: hex head, flat countersunk, acorn, and round head.

Female-type Anchor - Fixture will be removable

With a number of different female type anchors available, anchor selection depends on the type of bolt being inserted into the anchor as well as the quality of the base material. The sizes of these anchors are designated by the inside diameter of the anchor, which is the size of the bolt that will be inserted into it. The different female type anchors and their unique characteristics are listed below:

Concrete Screw - Fixture will be removable

Concrete screws are designed to tap threads into base materials made of concrete, brick, or block. They work well in mortar joints as well as in the solid and hollow sections of a block for light duty loads. They are available in a wide array of lengths in both 3/16" and 1/4" diameters and come in a range of different head styles, including hex head and flat Phillips for countersinking.

All of the fasteners described above are suitable for use in the concrete block, whether for the solid section of the block, the hollow portion, or the mortar joint. These fasteners may be used in light or medium load applications with a non-vibratory, non-shock load.

Hammer-type Anchor - Fixture will be non-removable

The hammer drive and nylon nail-it anchors, two fastener examples that fall into the hammer type category, result in a clean wall without protruding anchors. Both of these anchors are essentially non-removable and simple to use, but should only be used in light duty applications because the only diameter available is 1/4". The hammer drive anchor is produced with a low-profile mushroom head while the nylon nail-it anchor is available in three different head styles: mushroom, round, and flat countersunk.

Although some of the fasteners listed above may be appropriate for heavy-duty loads, the strength and integrity of the block will be limiting and will most likely fail with an exceedingly heavy load. Heavy-duty, non-vibratory, non-shock loads would require a through-bolted fastening technique or a concrete epoxy type fastener. Vibratory and shock loads would also require a through-bolted fastening system, a concrete epoxy type anchor, or a cast-in-place fastener.

To ensure safe mounting on any applications that require the fastening techniques outlined above, it is important to consult an engineer.

Bob Carlisle has been president of Concrete Fastening Systems, Inc. for 29 years, and has been involved in the concrete anchor business since 1981. By working on job sites as well as by meeting with engineers and architects, Bob has gained a wealth of information in the field of fastening to concrete. 

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