The hole in the masonry should be drilled by use of a hammer drill that is set in the hammer and rotation mode. This will ensure that the hole drilled will have accurate dimensions. Using a straight rotation drill may create a hole that is not shaped properly and may negatively affect the holding strength of the screw once installed.
Once the hole is drilled, it must be cleaned of all dust and debris. Using a wire brush, vacuum or compressed air will ensure that the hole is clean before installing the masonry screw.
The bit that is used in the hammer drill for the masonry screw has a carbide tip. The carbide tipped bit must meet ANSI standards B212.15-1994 to ensure the correct tolerance between hole size and masonry screw size requirements.
The 3/16” diameter masonry screw requires the use of 5/32” carbide tipped bit for drilling the hole. The 1/4” diameter requires the use of a 3/16” carbide tipped bit.
The length of the bit used should allow the hole to be drilled a minimum of 1/2” deeper than the masonry screw will penetrate the base material. The chart below shows the length of the drill bit to use with each length of masonry screw:
|Screw Length||Bit Length|
The masonry screw must be installed a minimum distance into the masonry to obtain minimum holding values. The masonry screw must be embedded a minimum of 1” and a maximum of 1-3/4” into the masonry base material. Less than 1” embedment will decrease the holding values and may provide no holding values at all. Attempting to embed a masonry screw deeper than 1-3/4” may cause installation problems, such as having the screw shear off or become stuck in the hole.
All base materials are different, and the masonry screws installed in concrete may act differently than those installed in brick or cinder block. The lead thread of the masonry screw cuts threads into the masonry. This lead thread can wear down, making it difficult or impossible for the screw to reach minimum embedment depths or depths leading up to the maximum embedment depth of 1-3/4”.
The length of masonry screw must be equal to the thickness of the material being fastened plus a minimum of 1” with a maximum embedment of 1-3/4”.
Two head styles are available: the hex and flat countersunk. The hex head masonry screws lengths are measured from underneath the head and are used in applications where the head of the screw is above the surface of the material being fastened. The flat countersunk is measured as an overall length which includes the head and is used where the head is countersunk in the material being fastened. The hex headed masonry screw requires a 1/4” driver for the 3/16” diameter screw and a 5/16” driver for the 1/4”. The flat countersunk requires a #2 Phillips driver for the 3/16” diameter and a #3 Phillips driver for the 1/4” diameter.
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.