Concrete fencepost insulators

Update April 2017 -- 1 year later the insulators are still anchored in place just as tightly as when I installed them.

A common sight in rural Slovakia is corroding chainlink fence held on concrete posts that have been, often, concreted into the ground.  As we have some of these relics on our farm, over the years I have tried a couple of different approaches to putting a hot wire on them-- variations on a theme of strapping insulators to the posts with cable ties.  It was not terribly effective.

 Recently I was thinking about this again and how to put multiple wood post screw insulators on one post effectively.  My first thought was simple take a lot of boards and screw insulators into them, then use wire to tie them to the post.  But this would involve a lot of wood, which would mean an extra cost as well as eventual problems with rot and a good bit of wire needed as well just for attaching to the posts.  The next thought was to drill through the post and attach the insulators with metric screw thread, nuts, and washers.  Then after having used polyurethane glue for the first time making the tool storage drawers, how I would do it all came together.

On the insulators I have the screw thread is 5.8mm and the smooth shaft is 4.8mm, so I used the 5mm SDS bit to drill the hole into the post.  Be sure to blow, or perhaps even better, use a stream of water to clear the concrete dust out of the hole (wetting the hole helps the glue set faster).  Attaching a piece of tape to the drill bit can help to ensure that the hole is deep enough for the insulator without going all the way through the post, as this sometimes knocks off a chunk of concrete from the back of the post, probably weakening it.

Then fill the hole with the polyurethane glue, and within the open time of the glue, screw in the insulator.  As long as the drill bit went precisely, the thread of the screw will slightly deform and make a tight fit right away.  But even if the bit jumped around and made a slightly large hole, the glue will still hold the insulator in fairly well.

Tools needed:

I tested several possibilities for holding the insulators:

  • 5mm hole without any glue
  • 5mm hole with PU glue
  • 6mm hole with PU glue
  • 8mm hole with plastic anchor
  • also tried a different pink glue I had on hand, but ineffective

The most satisfactory was the 5mm hole with PU glue, followed by the plastic anchor.  In both cases the insulator fit tightly, but it was possibly to unscrew it and then re-screw to the same tightness.  The 6mm hole with PU glue held, but unscrewing and then re-screwing resulted in a weak fit.  Likewise the hole without glue was initially tight, but after unscrewing and re-screwing was loose.  Not that one will be removing and reinstalling the insulators into the same hole, but I figure it is some simulation of wear over time.  The disadvantage of the 8mm hole is a larger hole which would potentially weaken the post, more likely to hit rebar and a bit slower to drill.  Economically, the glue is cheaper, but plastic anchors aren't costing much anyway, and potentially less messy.