post holes in rock with jackhammer?

[JasonB]

I need to get 10 4x4 posts set to finish my privacy fence. Unfortunately, these holes all hit solid rock within 2 to 12 inches. I have been told that a 60-90lb pneumatic jackhammer may be the answer to my problem. I can barely chip the rock with a 16lb rock bar, Any guess how the jackhammer will work before I drop $175 on rental? I need to get the holes to at least 24-30"

 

[Bob_VT]

Re: post holes in rock with jackhammer?

Jack hammer's break up rock or compact..... what you need to do is penetrate the rock. I would suggest a few ways.... First consider moving the fence and take the least resistance direction....

A hammer drill with a 1" bit. Sink in some threaded rods set in epoxy and attache the fence to those.

Trust me if you were in VT I have a fast fun method with the proper placement of explosives.....

 

[Bondo]

Re: post holes in rock with jackhammer?

A hammer drill with a 1" bit. Sink in some threaded rods set in epoxy and attache the fence to those.

Ayuh,.... I Agree Completely,.......

Hammer your 10 Holes at 1",+ bore out the 4X4s,+ drop them over the steel bar sticking up....
Just pieces of Rebar will work just as well as Threaded Rod......You might even be able to drive the Rebar with the 90# Hammer......
No Need to hammer out holes that'll directly take the 4X4s.....

 

[JasonB]

Re: post holes in rock with jackhammer?

Thanks guys. Unfortunately, moving the fence isn't an option.

Explosives would be my preference for all the grief this rock has given....

Many of the holes will work ok with the rods/rebar I think. Witha 6' olid privacy fence, I am a bit afraid of the pressure from wind splitting the post. I had also thought of trying to drill a hole the size of a tpost and epoxy it in as well to give the 4x4 some extra support. To get a hole that size is a whole other animal. 1" is all I can readily get my hands on.

Sounds like time to visit the tool store for a new hammer drill.

 

[Bondo]

Re: post holes in rock with jackhammer?

Sounds like time to visit the tool store for a new hammer drill.

Ayuh,.... For 10 holes,... I'd rent a 90# Hammer,+ Compressor,....
You can get the Bit to drill them with from the rental shop....

 

[JasonB]

Re: post holes in rock with jackhammer?

The rental shop said he would give me both a pointed bit, and a 1" chisel bit.

Also, I rechecked. What I call a jackhammer, they call a "rock drill". Does that make any difference?

 

[Bob_VT]

Re: post holes in rock with jackhammer?

Actually a great deal of the work depends on what the rock is. Yes a "star drill" bit will go into rock but you will not get a clean hole. if it is random loose big rocks or ledge.

The threaded rod and epoxy works great (holds most flag poles up like that) but be certain to absolutely clean out the dust and debris from the holes.

Depending on the height of the fence and the wind it will have to stand up to you might consider using threaded rod and steel pipe for the uprights posts.... fill them with concrete and they will not bend.

 

[JasonB]

Re: post holes in rock with jackhammer?

Best guess is limestone. 6' dog ear solid picket fence, posts on 8' centers, wind gusts up to 50+

 

[JasonB]

Re: post holes in rock with jackhammer?

I'm also thinking about adding a few trees/shubs/hedges outside the fence to act as windbreaks.

 

[Bob_VT]

Re: post holes in rock with jackhammer?

If you add in some trees and shrubs that would hide a guy wire or two. If the rock is that close to the surface..... how are you going to plant anything??

 

[JasonB]

Re: post holes in rock with jackhammer?

Good point...

 

[JasonB]

Re: post holes in rock with jackhammer?

Well, as a follow up, I found a workable solution to the problem....

I called a fence pro and got a quote on drilling those 10 holes. I told my wife the price..... she now wants to move the fence.

Oh well, I only have to move 26 posts to do it..... but its less pain than those 10 holes. Now I have to fill 20 something holes back in.....

 

[beerfilter]

Re: post holes in rock with jackhammer?

HEHE, sounds familliar .
Seen a lot of places here where you need HE to plant trees , dig post holes , set footers , etc..

Limestone is a good bet most places in TN .
The jackhammer rental is your cheapest and fastest approach , sans chemical persuasion .
Just make sure you clean out the hole well , back fill around the post with slightly damp clay , and , tamp the h*** out of the clay around the post .
Fill a few inches and tamp , a few more inches and tamp , etc...

Concrete works ok , especially in rock , but , in plain old soil , it may loosen over time.
If you get the bottom foot of the post tamped tightly , you will never have a problem unless the post rots or burns .

 

[JustJason]

Re: post holes in rock with jackhammer?

option b coulda been to build up a berm and pour your own concrete footer... if you built up a berm you coulda planted your shrubs too.