Block anchors are concrete fasteners that are designed to fasten an object to block used in the construction of homes and buildings. The concrete block is commonly called a concrete masonry unit or CMU. The typical block used in construction has large hollow cores. The hollow cores might have reinforcing bars placed in them and filled with grout to provide extra strength.
Mechanical type anchors are most commonly used for attaching an object to a block wall. A mechanical anchor is an expansion anchor that expands and exerts force against the block, holding the anchor in place. Concrete screws commonly referred to as a Tapcon®, work well in blocks because they tap threads right into the block to provide excellent holding values. There are a number of different styles of block anchors that can be used, with each one offering positive and negative qualities that are dependent upon their specific application.
The successful holding value of any block anchor chosen for a specific application depends on the block being fastened to. Block is a very poor base material for fastening because it is lightweight, porous and has large hollow cores. There are also inconsistencies from block to block. A block anchor may work well in one block and not as well in another within close proximity. Drilling into the section of the block that is hollow can cause the interior section of the block to spill out, leaving very little material to fasten to.
The mortar joints may be a space where a block anchor must be placed. The quality of fastening into a mortar joint depends on the quality and quantity of mortar. The mortar joint may be an excellent base material if enough mortar is in place and the mortar is of high quality. Small quantities and a poor mortar mix will most likely result in a poor base material for any type of block anchor to work well.
Bolting refers to the process of inserting a piece of threaded rod completely through the block wall and then placing a large plate washer and nut on each end. If possible, the through bolting method will give the best, most consistent holding values. However, in many cases, it may be impossible due to the lack of access to both sides of the block wall.
The sleeve anchor is the most popular anchor for fastening to block because of its variable expansion. The sleeve anchor is designed to expand over a wide area allowing the sleeve anchor to grab, and then expand once the solid block is reached. The sleeve anchor comes assembled with a nut and washer. Hole size is anchor size. They are available in stainless steel. A wide range of sleeve anchors is available for fastening to block from 1/4” to 3/4” and lengths ranging from 5/8” to 6-1/4”. The sleeve anchor also has a number of different head styles to choose from depending on the specific applications: acorn head, hex head, flat or round head. Sleeve anchors can be used in block or the mortar joint and they are simple to use and cost-effective. View holding values and technical information for the sleeve anchor or buy sleeve anchors now!
Unlike sleeve anchors for a block, concrete screws used in the block will not expand but actually, tap threads into the block. The concrete screw requires a pre-drilled hole and as it is inserted into the hole taps threads into the block to give excellent holding values. Tapcons can be used in both the block and mortar joint. They are available in two diameters and lengths ranging from 1-1/4” to 6” and come in coated carbon steel for use in indoor block applications and a 410 stainless steel for use in moist or outdoor block applications. The two head styles that are used include the hex slotted washer head and the flat countersunk Phillips. They are packaged 100 pcs per box with the one proper sized bit in each box. View concrete screw technical information or purchase Tapcons now!
Other block anchors are available and all work well in block base material. They are all female type concrete anchors and require a bolt and washer. They require spotting of the hole since the diameter of the hole that needs to be drilled is much larger than the diameter of the bolt inserted into them.
Below is a list of other block anchors:
1. Machine Screw Anchor
2. Double Machine Screw Anchor
3. Single Machine Screw Anchor
4. Lag Shield Anchor
As with any anchoring project, it is important to keep safety in mind and follow instructions carefully. Always remember to wear safety goggles, handle all tools with extra care and follow all technical specifications. This article is meant to serve only as a basic explanation of concrete fasteners. Always refer to manufacturer's instructions or consult a contracting expert during any anchoring project.