It is important to use the correct type of screw in certain situations to ensure that the application or installation is executed correctly and safely. The concrete screw is a special type of screw specifically designed to tap its own threads into a pre-drilled hole in a variety of base materials including concrete, brick and block. The brand name Tapcon® was the first concrete screw on the market, patented in 1976 by ITW Buildex. These screws are known for their ease of installation, superior pull-out resistance and strong holding values.
Concrete Screw Threads
In the concrete anchoring industry, the threads of these concrete screws are referred to as "High-Low". These "High-Low" threads allow for fast and complete dust removal during installation. This type of thread also permits the screw to tap threads consistently and delivers high quality performance. Dust removal is important because dust that is created in the hole when the threads are cutting into the base material must be removed as quickly as it is created. This ensures smooth and consistent installation, with less torque required to insert the screw into the base material.
If the dust is removed from the hole slower than it is created, a number of different problems may occur. The screw can bind up in the hole, preventing further insertion and/or prohibit the removal of the screw. Also, if the screw binds in the hole and too much torque is applied, the head of the screw can shear off. Since the lead thread is doing all the cutting of the base material, the quality of the steel and thread forming are extremely important.
Hole Requirements
As with all concrete anchors, the hole tolerance for a concrete screw is critical. For a 3/16" diameter screw, the hole diameter is 5/32". When using a screw with a 1/4" diameter, the required hole diameter is 3/16". Always use a hammer drill and matched tolerance carbide tipped masonry bits when
installing concrete screws.
The hole should always be drilled at least 1/4" deeper than the required penetration. This will guarantee that the screw does not bottom out before it reaches the desired depth of embedment. If the screw bottoms out because the hole is not deep enough; it will stop, bind up and probably shear off at the head. Masonry bits come in different lengths to accommodate the different lengths of screws that are available. These bits are typically available in 3-1/2", 4-1/2" and 5-1/2" lengths.
Embedment Requirements
Concrete screws require a minimum embedment of 1" and a maximum embedment of 1-3/4" into the base material. An embedment of less than 1" should not be used because this will diminish the holding values of the screw. True holding values are also not known in this situation. Trying to embed the screw deeper than 1-3/4" could cause a variety of problems including:
- Causing the screw to bind in the hole prohibiting it from going any further
- Not being able to remove the screw
- Shearing off at the head
It is also important to note that the harder the base material is the less the maximum embedment should be. The lead thread may lose its ability to cut into the base material after 1-3/4", especially if the base material is extra hard or abrasive.
Determining the Length of Concrete Screw to Use
Each unique application will require a different length of concrete screw. To determine the length of screw required, follow the instructions below:
Thickness of the material to be fastened + a minimum of 1" or a maximum of 1-3/4"=
Length of screw required
Keep in mind; all concrete screws are measured from under the head. For example, when fastening a 2x4 to concrete, the 2x4 is 1-1/2" thick. Take 1-1/2" plus a minimum of 1" and a maximum of 1-3/4" embedment. This provides a total of 2-1/2" to 3-1/4" for the screw length. Concrete screws are available in lengths of 2-3/4" and 3-1/4". In this particular case, the 2-3/4" screw would be the proper choice, as the embedment would be 1-1/4".
Installation of Concrete Screws
The installation of a concrete screw is quite simple. Installation can be completed in three steps:
1. Using a hammer drill and a correctly sized carbide tipped masonry bit, drill a pilot hole ¼" deeper than the recommended anchor embedment.
2. Clear the hole of all debris.
3. Using a standard drill with the appropriate hex or Phillips socket, drive the concrete screw into the pre-drilled hole until the screw is fully seated.
* Be careful not to over-tighten the screw - this will cause the screw to spin
in the hole, stripping the threads.
For more detailed step by step information, please view this Concrete Screw Installation Video.
Applications for Concrete Screws
Concrete screws are very versatile and are ideal for use in light to medium duty fastening applications. These screws come in a variety of sizes and styles that are easy and fast to install. After installation, concrete screws can be removed without disturbing the base material. These screws can also be installed close to an edge. The different lengths can be used in applications when the fastening material has a thickness of up to 5". This wide range of lengths allows the screws to be used in many applications including: studs, plywood, electrical boxes, exterior insulation systems and door bucks.
Additional Information
All concrete screws have different holding values which depend on the type of base material, screw diameter and depth of embedment. Concrete screws are available in two different head styles - hex washer head or flat Phillips countersunk. These screws typically come packaged in boxes of 100 with one matched tolerance drill bit.
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 as a basic overview of the steps for completing this project. Always refer to the manufacturer's instructions or consult a contracting expert during any anchoring project.
Article Written By: Bob Carlisle, President of Concrete Fasteners
Tawny Sikon, Operations Manager
Concrete Fasteners, Inc. has over 40 years experience selling concrete fasteners. We ship to all 50 states and many countries. 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 order is received.
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