When tapping threads into masonry, the lead thread does all of the cutting of the masonry material and is designed to cut threads up to 1-3/4” in depth. The abrasiveness of the masonry will determine the exact depth that any specific screw can tap. The lead thread will dull and hit a point where it will no longer be able to cut threads and will stop screw penetration. As the threads are cutting into the masonry, dust is created. The threads are designed to allow the dust to be removed and to prevent interference with the screw installation. Therefore, the hole drilled in the masonry must be slightly deeper than the screw will penetrate to allow space for the dust that is created during the taping process to fall into and out of the way.
Diameter of Hole
The hole diameter is critical and must be drilled in accordance with the manufacturer’s instructions. The guidelines for masonry screw anchors are as follows: the 3/16” diameter requires the hole diameter to be equal to 5/32” and the 1/4” diameter requires a 3/16” hole. The hole must be drilled using a carbide drill bit that meets ANSI standards. ANSI standards ensure proper hole dimension tolerance requirements. Any variance in hole size will affect the holding values and may make the holding values not existent.
Making the Hole
The hole in the masonry must be drilled using an ANSI standard carbide tipped bit used in a hammer drill that is set in the hammer and rotation mode. This will ensure that the hole is the proper shape and tolerance in order to allow the screw to obtain minimum holding values. Once the hole is drilled, it must be cleaned of all dust and debris or holding values may be affected. Using a wire brush, compressed air or vacuum in combination is usually sufficient to clean out the hole before inserting the screw.
Dimensions for Self-Tapping Masonry Screws
The dimensions of all masonry screws are described with two numbers. The first number represents the diameter of the screw and the second number equals its length. They come in two diameters of 3/16” or 1/4”, with each diameter available in a number of different lengths. Each diameter comes in lengths from 1-1/4” to 6”, but not all lengths are available in both diameters. The diameter of the screw used for a specific application is determined by the holding values required and the diameter of the hole in the item being attached. The length of screw used is based on the thickness of the material being fastened. The length of the screw used for any specific application is determined by adding the minimum embedment of 1” the thickness of the material being fastened. This will give you the minimum length of screw that can be used. The maximum length of screw is determined by adding the thickness of the material being fastened to the maximum embedment of 1-3/4”.
Masonry screw anchors are available in two different head styles designed for different types of applications. If the application calls for the head to be countersunk in the material being fastened then the flat countersunk phillips screw should be used. If the head of the screw will be on top of the surface of the material being fastened then the hex washer head should be used.
Types of Self-Tapping Screws
Masonry screws are manufactured from carbon steel that has a blue coating or from a 410 stainless steel which also has a protective coating. The standard blue coated masonry screw is for use in indoor applications where moisture is not present. For outdoor use or in moist atmospheres, the 410 stainless steel should be used.
The Tapcon brand is the original masonry screw and is still manufactured in the United States of America. For the best price and availability, Confast.com, a division of Concrete Fastening Systems, Inc., has all sizes in stock and will ship your order the same day it is placed. Our shipping is always free in the continental USA.
Please remember with all fastening jobs to keep safety in mind. Always follow safety instructions on all tools, and refer to manufacturer's installation instructions when available and always remember to wear safety goggles!
Article written by: Bob Carlisle, President Concrete Fastening Systems, Inc