Tags: Stainless Steel Fastener Self Tapping Screw Self Drilling Screw
In many construction applications, concrete anchors must be fastened to a concrete block to hold a fixture or item of some kind. When installing these concrete anchors, special care must be taken to ensure safe and proper fastening. When fastening to concrete blocks, a number of specific considerations must be taken into account. These include what part of the block to drill into as well as which type of anchor would work the best in the specific application.
What is a concrete block?
A concrete block, cement block, foundation block or concrete masonry unit (CMU), is a large rectangular block used primarily in the construction of walls. Concrete blocks are made from precast concrete, i.e. Portland cement, water and aggregate. The aggregate used for high-density blocks is usually sand and/or fine gravel. Lower density blocks, more commonly known as cinder blocks, may be produced using cinders as aggregrate. These blocks are then layered and stacked vertically to form a wall, and are held together using concrete mortar.
Determine where in the block the anchor should be placed
Before choosing the correct anchor for an application, it is necessary to consider where in the block the fastener should be positioned. Will the fastener be placed in (a) the mortar joint, (b) the solid section of the block, or (c) the hollow section of the concrete block? Some applications may allow each fastener to be placed in the same part of the block while other installations require that each anchor be placed in different sections of the block.
Each section has unique advantages and disadvantages. Fastening into the mortar joint can be an excellent option depending on the quality and quantity of the mortar used to set the block in place. The solid sections of the block usually offer the best quality fastening. This will depend on the distance of the fastener to the unsupported edge of the cavity and the quality of the material from which the block is made. The hollow section of the block is the least desirable section of the block in which to fasten but sometimes can not be avoided. When fastening into the hollow section of a block, there are a few considerations to keep in mind:
(1) When drilling into the block with a hammer drill, the block will spall. This leads to a cone shaped space, with the point of the cone closest to the surface of the block.
(2) When inserting an anchor into this area, whether it’s a fastener that exerts pressure or a concrete screw that taps threads into the base material, the holding values will be diminished or become non-existant.
(3) The fastener must not penetrate the wall into the cavity itself.
Determine the type of load to be fastened
The next step in the process is to ascertain the type of load that is going to be anchored. There are three questions that will help determine the type of load each application produces:
(1) How heavy is the item that is being fastened to the block wall?
(2) Will the load be a vibratory load?
(3) Is the load going to be placed where a shock load could occur?
Determine the type of anchor required
Lastly, the type of fastener required for the application must be determined. There are four options available that can be used in concrete block:
(1) Stud-type anchor: where the stud will stick out from the wall. Example: Sleeve Anchor
(2) Hammer-type anchor: where the stud does not protrude from the wall, for a finished look. Example: Hammer Drive, Nylon Nail-It
(3) Female-type anchor: where a screw is inserted into the anchor for a finished look. Example: Machine Screw Anchor, Lag Shield Anchor, Single Expansion Anchor, Double Expansion Anchor, Leadwood Screw Anchor
(4) Concrete screw: screwed directly into the block for a finished look
If using a stud-type anchor, female type anchor, or the concrete screw- the fixture, or item being fastened, can be removed at any time with little or no damage to the concrete block. However, hammer-type anchors are permanent installations. Removing these fasteners will greatly damage the concrete block and possibly the fixture as well.
Anchor types that can be used in concrete block applications
Stud-Type Anchor – Fixture will be removable
Sleeve anchors come in the widest variety of sizes for applications that fall into this category. Anchors with diameters ranging from 1/4″ to 5/16″ are sufficient for most light duty applications while the 3/8″ and 1/2″ diameters are adequate for most medium duty situations. Sleeve anchors with diameters of 5/8″ and 3/4″ are usually considered heavy duty anchors. An engineer should be consulted every time concrete anchors are used for heavy loads. This anchor is very versatile because there is a wide range of lengths available allowing materials of many different thicknesses to be attached to a block wall. The sleeve anchor also comes in a variety of head styles – hex head, flat countersunk and acorn or round head for aesthetics.
