Information About Fastening to Concrete
Published by Robert Carlisle on Sep 30th 2009
Concrete fastening is the process of fastening an object to concrete, brick or block base material. The type of fastener that should be used in any specific application and the drilling of the hole in the concrete are both important aspects of concrete fastening. The two basic types of fasteners that are used for concrete and masonry applications are the mechanical type and adhesive type anchors. The mechanical type anchor is an anchor that creates friction between itself and the base material while adhesive anchors use epoxy or chemicals to adhere to the base material. Mechanical type anchors are best used in static type* applications. Adhesive anchors are most effective when the application includes a dynamic** or shock loading*** attribute.
* load that does not move ex: light fixture attached to a concrete wall
** load that is constantly moving ex: conveyor belt attached to a concrete floor
*** load with occasional movement ex: dock bumper
The drilling process includes a drill bit and a drill. Drill bits that are used should have a carbide tip and must meet ANSI standards. ANSI standards were developed to ensure that the tolerance of the bits meets the tolerances of the concrete anchors. Hole tolerance is critical when using these fasteners. If the hole doesn't meet the hole size required for the anchor, the anchor will not work and the holding value will be zero. The drill that is used is one that rotates the bit as well as moves the bit up and down. The up and down motion, called the hammer motion, breaks up the concrete or masonry material and the rotation pulls the dust out of the hole.
Concrete anchors and fasteners are designed for use in concrete as well as brick or block material. Some concrete anchors can only be used in concrete and others can be used in all three base materials. The versatile anchors can be used in many different types of applications but have lower holding values. An important consideration is that an anchor that is designed for use in concrete only will provide better, more consistent holding values in concrete than anchors that can be used in all varieties of base materials. Concrete anchors come in two basic types: male and female. Male type anchors can be placed through the fixture being fastened while the fixture is in place and sticks out from the base material once installed. Female type anchors are placed into the base material and a separate bolt is inserted through the fixture and into the concrete anchor. Female anchors also require spotting of the hole which includes marking where the hole needs to be, moving the fixture, drilling the hole and then moving the fixture back over the hole then inserting the bolt into the concrete anchor.
Concrete Drill Bits
Concrete drill bits have three basic parts: carbide tip, the flutes, and the shank. Concrete drill bits are bits that have a carbide tip- which is a very hard material that is perfect for drilling concrete or masonry. The carbide breaks up the base material and is also the part of the bit that is matched to the proper tolerances for each concrete anchor- based on ANSI standards. The flutes are critical in the removal of masonry dust from the hole. The hole can only be drilled as fast as the material can be removed. Matching the correct bit to the hammer drill is essential for efficient hole drilling. Each bit has a shank, which is the part that goes into the chuck of the drill. Different types of drills will require different types of shanks. These different types of shanks include straight shank, SDS drill bits, SDS plus, SDS Max bits or spline. These designations describe the type of connection between the bit and the chuck for each bit.
Below is a further explanation of each type of shank:
Straight: either round or with flats on it and are designed for use in a Jacobs style chuck or a chuck that uses a chuck key.
SDS/SDS Plus: stands for Spline Drive Systems and fits into an SDS chuck, which is a keyless chuck. The SDS bit is about 3/8" round with two groves and two notches that cut into the shank. The grooves lock the bit into the chuck to ensure proper rotation and the notches allow the bit to move back and forth for the hammering motion.
SDS Max: a larger version of the SDS/SDS Plus. Shank is about 3/4" and is designed for larger drills. The spline bits have groves around the whole circumference of the shank that fit into larger drills.
Concrete Hammer Drills
Concrete hammer drills are required for drilling into concrete, brick or block base material. Unlike steel, wood or other soft materials, concrete requires that the drill pulverizes the material and then be removed from the hole. This pulverization of the base material is achieved with the use of a hammer drill. Hammer drills do two things: it rotates the bit and it moves the bit back and forth in a hammer-like motion. The development of hammer drills over the years has resulted in two different methods for accomplishing the rotating and hammering motions needed for drilling into concrete: the mechanical hammer drill and the electro-pneumatic hammer drill. Mechanical hammer drills hold the bit tight in a Jacobs style chuck that uses a key. These drills hammer at a rate of 20,000-30,000 times a minute using very small strokes and drills holes very efficiently. This type of hammer drill has the option to rotate only or rotate with hammering. The electro-pneumatic hammer drill hammers at a rate of 300-900 times a minute. The hammer motion is very hard since the bit actually moves and efficiently breaks up the concrete. This type of hammer drill also has a switch that allows for rotation with hammering, hammering only and rotation only.
Applications that require any amount of concrete drilling and fastening should be approached with safety and best practices in mind. The usage of all of the correct equipment will help ensure that your concrete drilling and/or fastening application gets completed safely and correctly.