The Metal-to-Concrete Connection
Installation steps you need to know before you drill and anchor
Almost every commercial construction project requires crews to
attach something to concrete, and often it is a metal screen or
other metal building product. But there are few standardized
guidelines for the proper way to do it, and reports from the field
reveal that installation processes vary considerably not only from
job to job but from crew member to crew member. When installed
correctly, though, anchors bonded or mechanically attached inside
drilled holes can be as strong as or stronger than cast-in-place
systems. However, if the right anchor is not installed correctly, a
complete assembly failure can occur.
The whole hole
Anchoring into a concrete wall for this connection requires
drilling a precise pilot hole with very specific size and depth
requirements. These requirements determine much of the anchor's
holding success. However, "there is no standard, like an ASTM or
ANSI standard, that is generic and specifically states how the
drill hole is to be created," says Donald F. Meinheit, affiliated
consultant for Wiss, Janney, Elstner, Associates
Inc., Chicago. "The directions for drilling the hole, that is,
the diameter of the drill bit and depth of the hole, are listed for
each anchor in the manufacturer's printed installation instructions
While hole diameter size varies, most are close to 1/4-inch. If
a threaded anchor is used, the pilot hole should be smaller than
the diameter of the concrete anchor. The hole must be larger if a
wedge, sleeve, epoxy or a "spike" type anchor is used. Most holes
are 1/4- to 1/2-inch deeper than the anchor itself. Refer to the
manufacturer's recommended instructions. Most anchor manufacturers
base hole size and other information on independent lab results
that determine an anchor's rated capacity.
There are many different types and shapes of concrete fasteners
and each anchor's installation is unique. Be sure appropriate
installation techniques and proper tooling are used to ensure
correct pilot holes and holding values. "The anchor's embedment
depth should be based on the loading conditions the anchor needs to
withstand," says Chris La Vine, senior engineer at Simpson Strong-Tie, Pleasanton,
The drill and the drill bit
To drill holes for concrete anchors, there are three generally
accepted methods: rotary-hammer drilling, rock drilling (rotation,
percussion and air pressure) and core drilling. According to
Meinheit, there is no one method that is most appropriate for each
type of anchor. Mechanical expansion anchors and concrete screws
generally need an accurate diameter, whereas, adhesive anchors need
a good roughened hole to achieve a bond between the adhesive and
the concrete substrate.
Hammer drills are small tools designed for drilling holes up to
about 1/2-inch in diameter. Rotary hammers range in size, some are
capable of drilling up to 1 1/2-inch diameter holes. "These tools
drill and hammer at the same time," says Jeff Dunagan, senior
engineer, at Simpson Strong-Tie. "To create a hole in concrete, a
chiseling action is needed. To make the holes round, rotation of
the chisel is needed. These tools provide these two actions
Most drill bits use a SDS chuck. Standard drill bit sizes are
specified in the American National Standards Institute (ANSI)
International Standard B19.11M. "Use a carbide tip drill bit
specifically designed for concrete and masonry that is the correct
diameter based on the type of anchor used," says Joe Stager, vice
president of product development and marketing, Triangle Fastener Corp.,
Carbide drill bits are typically made of tungsten carbide that
is nickel based with a carbon coating. This type of drill bit has
many applications, such as drilling into stone, metal and removing
screws that will not come out of metal. Standard drill bits are not
that strong and are made of a lesser quality material that can bend
or break when drilling into hard materials like concrete.
A carbide chisel built into the bit's end can chisel the hole to
the desired depth. The flutes on the bit's shaft remove the
drilling dust. These bits have different shank configurations that
mate with different types of hammer drills and rotary hammers.
Always use a drill bit that complies with ANSI B212.15-1994,
American National Standard for Cutting Tools-Carbide Tipped Masonry
Drills and Blanks for Carbide-Tipped Masonry Drills, American
National Standards Institute, which is the standard for carbide
blanks used on single-point tools.
Anchor installation steps
The procedure for drilling into concrete is virtually the same
for almost any style anchor. The following installation steps are
provided by David Garfield, owner of Wej-It Fastening Systems, a
division of Mechanical Plastics Corp., Norwalk, Conn.:
• Buy a good quality drill with variable speeds, hammering
function, depth setting and power. Using a cheap drill with less
power will potentially make holes that aren't deep enough or off
• Read the user's manual for the drill, and get to know what all
of the knobs and controls are for.
• Set the depth-some drills will have a depth setting or depth
control bar. If the drill does not have depth control, measure and
mark the required depth with tape.
• Hold the drill properly with one hand like a gun and with your
index finger on the trigger. If the drill has a handle for your
other hand to hold, use it. Otherwise put your other hand at the
back of the drill.
• Mark the point on the concrete wall, floor or ceiling where
you want to drill. Place your drill on the mark and apply enough
pressure to hold it in place-don't press it too hard. Drill using a
low speed or in short bursts. Make a shallow hole that will guide
the drill so the hole is made exactly on the mark.
• Using a high speed and the hammer function (if the drill has
it), drill into the shallow hole made in the previous step. Use
some force against the wall, especially if the drill is not too
powerful. Stop once you reach the desired depth.
• Sometimes drilling a hole won't go as expected. You might hit
something behind your substrate or a hard piece of concrete. If
this happens, insert a masonry nail into the hole and hammer to get
rid of the blockage. Insert the drill back and continue
• Once the hole is drilled properly, insert a fastener/anchor
and follow the instructions for proper installation.
Remember to use earplugs and safety goggles during drilling and
to always follow the manufacturers' safety precautions when using
Different concrete types have an impact on anchor holding power.
"Anchors in lower strengths of concrete perform differently than
the same anchors in very high-strength concrete," Meinheit says.
"If the concrete is very high strength there may be difficulty in
getting some of the anchors to function properly."
Some concrete may be too brittle to withstand the installation
techniques required for a specific anchor. The concrete's rate of
strength gain is affected by use of supplementary cementitious
materials (SCMs), like fly ash and slag cement. The more Portland
cement that is replaced with SCMs, the slower the strength
Different types of concrete require
different anchors that can be used. "Wedge anchors are used for
concrete aggregate that is harder than 2,000 psi," says Garfield.
"When anchoring into less dense concrete, hollow block or brick, we
recommend using sleeve anchors and other anchoring products. Every
application and environment will determine which anchor or drill
bit will be the correct product to use."
Regardless of the type of concrete used, removing the concrete
spoil or dust is important after drilling. "For a mechanical
expansion anchor, the concrete spoil is usually removed by blowing
the hole with compressed air," says Neal S. Anderson, PE, SE, vice
president of engineering at the Concrete Reinforcing Steel
Institute, Schaumburg, Ill. "For an adhesive anchor, the hole
cleanout procedure is quite important and is prescribed through the
The metal's grade, thickness, size and weight being attached
impact anchor installation and selection. The anchor's holding
strength must exceed the load value of the tensile load being
applied by the metal being attached or pullout will occur.
The larger the loads, the larger and deeper the anchors or the
more anchors you need. "If we are talking about heavy-industrial
loads, the postinstalled anchor is not the correct choice," says
Meinheit. "If embedment is into a member that is heavily reinforced
with reinforcing bars, drilling the holes is very difficult without
cutting other structural reinforcing steel. For 'lighter' loads,
the post-installed anchor is probably easy and less expensive than
having the formwork contractor locate anchors before the concrete
Do not connect metal directly to concrete without allowing for
expansion and contraction. Direct attachment will result in oil
canning, sheet slotting and fastener loosening. "A 20-foot-long
panel will grow about 1/8-inch with a 100 degree temperature
change," says Rod Roberts, field services manager, Varco Pruden Buildings, Turlock, Calif. "While
this doesn't seem like much, it will be a big problem. The bottom
end of the panel (corrugated vertically type) can be directly
fastened, but all fasteners above this location should have
clearance holes or mount the panel to a zee-shaped furring
ACI and adhesive anchors
Recently the American Concrete Institute (ACI) published a
design code that includes adhesively bonded anchors for the first
time. Adhesive anchors are very sensitive to installation
conditions and the code writing committee required that any
adhesive anchor that is installed and had to carry a sustained
tension load had to be installed by a certified Adhesive Anchor
"ACI and the Concrete Reinforcing Steel Institute (CRSI)
partnered to create a certification program," says Neal S.
Anderson, PE, SE, vice president of engineering at the Concrete
Reinforcing Steel Institute, Schaumburg, Ill. "Adhesive Anchor
Installer Certification is a new requirement in ACI 318-11,
Building Code Requirements for Structural Concrete, for anchorages
in sustained tension loading conditions and installation
orientations from horizontal to vertically upward."
Also important is the fact that "any anchor designed using the
design rules in the ACI code has to be qualified using a very
comprehensive procedure," says Donald F. Meinheit, affiliated
consultant for Wiss, Janney, Elstner, Associates Inc., Chicago.
"This procedure is a standard that every manufacturer has to use.
The procedure 'grades' the anchor on its performance and depending
on the grade, the anchor's strength can change. The anchors
designed using the ACI code are very thoroughly evaluated for their
performance. Installation into the concrete is an installation
issue that for anchors, except for adhesive anchors, is not
controlled by the ACI code."