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.
Anchors for Block
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 block 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
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.
Block Mortar Joints
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
Bolting Through the Block
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.
Sleeve Anchors for Block
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 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 are 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 into the 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!
Tapcon Concrete Screws for Block
Unlike sleeve anchors for block, concrete screws
used in block do not expand but actually tap threads into the block.
The concrete screw requires a predrilled 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 inlcude the hex slotted washer head and the
flat counter sunk 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
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.
Article Written By:
Bob Carlisle, President of Concrete Fasteners
Concrete Fasteners, Inc. has over 40 years of experience selling concrete fasteners. We can ship out one box or a whole pallet of concrete anchors. Our products are of the highest quality... "your satisfaction is guaranteed". We ship all orders the same day the order is received.