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Tapcon Breaking

Published by Robert Carlisle on Feb 27th 2011

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Tapcons breaking or shearing off during installation may happen occasionally due to a number of factors.  If a tapcon does break, it usually occurs within about 1/2” prior to full installation. Many generic concrete screws may have this breaking problem due to the inferior steel and manufacturing process. The American made tapcon brand concrete screws sold at www.concretefasteners.com have less breaking than the generic tapcons.

Hole Size
Hole tolerance is critical when installing a tapcon cement screw.  The proper size bit must be used and the hole must be drilled using a hammer drill in the hammer mode.  The carbide tipped bit must meet ANSI standard and be the correct diameter for the diameter of tapcon being used.  The 3/16” tapcon needs a 5/32” bit and the 1/4" tapcon needs a 3/16” bit.

Base Material
On some occasions, the base material is so abrasive that the hole tolerance is not able to be maintained along the entire length of the hole.  The deeper into the base material the hole is drilled then the smaller the hole will become. This is due to the carbide tip of the bit being worn away as the hole is being drilled.  Once the tapcon is inserted into a hole that is drilled in decreasing the size, the tapcon will be driven into the base material until the hole gets so small that the tapcon can no longer penetrate further. At this point, if more torque is applied to the tapcon then the shank of the tapcon will give way and break or shear off.

Depth of Hole
The hole in the base material must be drilled to a depth that is a minimum of 1/4” deeper than the tapcon will penetrate.  This extra space at the bottom of the hole allows for a collection area for dust that is created during the tapping process to fall.  The dust collected in this extra space will avoid having the tapcon bottom out in the hole.  If the tapcon should bottom out before the head is snug against the material being fastened, any additional strong torque applied to the tapcon may then break or shear off the shank of the tapcon.

Maximum Embedment
The tapcon screw has a maximum embedment depth of 1-3/4”.   The total overall length of the threads on the tapcon measure 1-3/4”. A 6” tapcon the threads will only measure 1-3/4”.  The threads of a tapcon tap threads into the base material with the lead thread doing the entire cutting.  The lead thread, depending on the abrasiveness of the material will wear as the tapcon is inserted into the hole.  Any embedment greater than 1-3/4” may result in the lead thread being worn to the point that it may no longer be able to cut the base material.  If this happens then the tapcon will no longer penetrate the base material.  Continued strong torque will cause the tapcon to break or shear off.

Length of Tapcon - the thickness of the material being fastened and the embedment depth determine the length of the tapcon.  To figure out the shortest tapcon to use for any application, add the minimum embedment of 1” to the thickness of the material being fastened.  As an example, when a conduit strap is being fastened to concrete and the conduit strap is 1/4” thick, add this to the minimum embedment. The minimum total length of tapcon to use would be 1-1/4”.  The maximum length of tapcon to use is figured out by adding the thickness of the material to the maximum embedment of 1-3/4”.

Torque Setting
Each application is different and the torque setting on the drill may be different for different types of base material.  The correct setting for driving a tapcon concrete screw without breaking or shearing off is determined by using the lightest setting and then moving up until the tapcon concrete screw is set tight against the fixture being fastened.  It is very important that the tapcon is not over torqued.

  • The base material may give away and the tapcon will spin in the hole because the threads in the base material have been stripped.
  • The tapcon may break or shear off if the head of the tapcon is torqued beyond its capabilities.
  • Tapcons are case hardened so the outer layer of the shank of the tapcon may crack or over stress if torqued at a high level.  This may cause a situation where the holding values are weakened. The interior steel of the tapcon is exposed to the elements and may rust sooner and faster, which will ultimately lead to fastener failure

Installing Tapcons

  • With a hammer drill in the hammer mode, drill a hole in the base material using the correct diameter of carbide tipped drill bit that meets ANSI standards.
  • Drill depth of the hole to a minimum of 1/4” deeper than the tapcon concrete screw will penetrate the base material.
  • Using a wire brush, compressed air or vacuum, clean the hole of all dust.
  • Insert tapcon through the hole in the fixture and into the hole in the base material.
  • A wrench or drill can be used to turn the tapcon clockwise until the head of the tapcon is snug against the surface of the fixture being fastened.

Tapcon Installation Video

Tapcon Not Suitable
Tapcon may not work in all applications all the time, which is a reason for the different types of concrete fasteners.  The base material may be too abrasive or too hard for the threads of the tapcon to tap.  The base material may be too soft or sandy and not allow for the tapcon threads to hold properly.  

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