- It is hollow, brittle, and inconsistent
- The holding power depends on the quality of the cinder block
- The pullout value changes in relation to the quality and quantity of mortar placed in the joints between cinder block
- Expansion – an expansion type anchor can be used in solid sections and mortar joints with great success for both heavy-duty and light-duty. If used in the hollow section, the holding values of this type anchor will depend on the amount of base material left that the expansion anchor expands into.
- Concrete Screw – the masonry screw, or tapcon, taps threads in the base material and can be used in all three sections. The holding values of concrete screws are totally dependent on the quality of the base materials’ ability for thread tapping. In the hollow section, it is important to remember that the concrete screw, or tapcon, must be embedded into the base material a minimum of 1”. Masonry screws can be found with a hex head or phillips head.
- Through-Bolt – drill a hole through the width of the cinder block, using a plate washer and nut on one side and a nut and washer on the fixture side. This fastening method and drilled hole probably gives the best most consistent holding values and is easily done if both sides of the cinder block are accessible.
- Epoxy – concrete epoxy fastening method can be used and gives great holding strength. It is excellent in vibratory shock loading applications. A screen tube must be used in conjunction with threaded rod and a nut and washer. Using the screen tube with the epoxy allows for two fastening techniques in the hollow section of the cinder block. The first technique is through the adhesive strength of the epoxy. The second technique is achieved through the keying action of the epoxy once hardened in the screen tube and hollow inside wall of the cinder block.
Fastening to Cinder Block
Cinder block is a popular building material used all over the world for many types of light-duty to heavy-duty applications. It is strong, fairly lightweight, and can be used for many building projects, including attaching furring strips. Cinder block, also known as CMU and block wall, is not costly when compared to other building materials.
It is important to know that the popular wedge anchor should be used in solid concrete applications, such as fastening to a concrete wall. Wedge anchors should never be used in a block wall or any hollow base material.
Cinder block can sometimes be difficult for fastening:
Drilling into a Cinder block
When drilling into a cinder block to place a concrete anchor, a hammer drill must be used with a drill bit that has a carbide tip. Drilling into the solid section does not create many problems when using a masonry bit. The hammer drill will drill the hole easily into the cinder block. If the pilot hole is drilled in the area of the hollow section, inside spalling may occur. This happens because the tip of the masonry bit gets too close to the inside non-supported edge of the CMU block. This could cause a cone-shaped section to blow out, leaving less material for the concrete fastener to grab. Once this happens, the holding power of the concrete fastener and concrete anchor will lessen.
Many times the masonry anchor location must be right by the holes in the fixture being attached to a cinder block. In that case, there is not much choice in the location of the concrete fastener. Fastening into the solid section usually allows for the best cinder block fastening as compared to using a hollow part of this base material. The mortar joint can be a great place to position a masonry anchor, but the holding values will again depend on the quality and quantity of mortar in the joint. When selecting a masonry fastener for outdoor projects, stainless steel should be considered for better rust resistance. Also, stainless steel is available in different grades.
Types of Best Cinder Block Fasteners
Types of Expansion Concrete Block Anchors
Sleeve Anchors – sleeve anchors have excellent holding values in the block and can be used in all three sections of the cinder block with good success. They are easy to use; come pre-assembled and come in a variety of different diameters and lengths to meet most cinder block fastening applications. Sleeve anchors can be found in a number of different head styles of acorn, hex head, flat Phillips and round.
Lag Shield Anchors – have been used for many years, can be used in all areas of the cinder block. Lag shield anchors come in a short or long version. The short version is used in base material that is very hard. The longer version is good in base material that is softer or maybe has less quality. Lag shield anchors come in diameters ranging from 1/4” to 3/4”.
Single Expansion- excellent female fastener for the solid section of a cinder block should not be used in the hollow section because all of the holding strength comes from a single source and the length of the expansion is minimal. A bolt must be purchased separately that has national coarse threads. The single expansion anchor comes in diameters from 1/4” to 3/4”.
Double Expansion – an excellent fastener for both the hollow or solid section of the cinder block and works well in the softer base material. The double expansion anchor expands along the whole length of the anchor making it ideal for applications where the base material is suspect. Each double expansion anchor requires that a bolt with national coarse threads be used and purchased separately. The double expansion anchor comes in six diameters starting at 1/4” through 3/4”.
Machine Screw Anchor – is best used in the solid section of a cinder block because it requires the bottom of the hole to be used for proper setting and expansion. The machine screw anchor needs to be set using a setting tool. To be set correctly, the anchor must sit against a solid base material when a hammer strikes the setting tool. Using a machine screw anchor into the hollow section can be done using a special hollow-set machine screw anchor setting tool manufactured by Greenlee. Machine Screw anchors come in diameters of #6, #10, 1/4”, 5/16”, 3/8”, 1/2”, 5/8” and 3/4”.
Hammer Drive Anchor – is a light duty anchor that can be used in the solid section and the hollow section if enough base material is left after the drilling process is complete. Hammer drive anchors are simple to use and come complete with the nail and anchor body pre-assembled. The head style of the hammer drive anchors has a mushroom head that measures about 1/2” across, making it perfect for applications where pullover is of concern. Once the nail is set in the anchor body of the hammer drive anchor, the anchor cannot be removed without cutting off the head. The hammer drive anchor comes in two diameters of 3/16” and 1/4” and in various lengths for the different thickness of the material being fastened to the cinder block.
Each of the best fasteners for concrete block anchors require specific installation steps.
Although exact installation instructions for a specific anchor can be found in the manufacturer’s instructions, the following are general steps for installation:
- Drill a hole in the cinder block or mortar joint using a hammer drill with a carbide tipped bit that meets ANSI standards. Make sure that the drill bit is the correct diameter for the anchor being installed. The drill bit size for the sleeve anchor and the hammer drive anchor is equal to the diameter of the anchor being installed. The female type anchors need a hole to be drilled that is equal to the outside diameter and not the designated diameter.
- Once drilling is complete, clean out the hole of all dust and debris, using a wire brush, compressed air or vacuum. Insert the anchor into the pre-drilled pilot hole in the cinder block and expand as needed.
- Concrete screws and tapcon need a hole to be drilled in the masonry that is smaller than the designated diameter. All masonry screws' packaging will show the best size of drilled hole to use.