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Old 05-02-2009, 09:27 PM   #1
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Re-using post holes in concrete


Replacing deck and fence between driveway and house. Fence posts were (before they rotted out) 4 x 4 set 24" deep in concrete which is now covered over by the asphalt driveway. The other side of the posts is a 4" concrete slab which we'll be decking over, up to the house.

We got a few of the posts out intact. For the rest there's still wood down in the holes. We've tried drilling it out, hacking it out with every tool we could find. What's left is a spire of the remaining heartwood and the auger bits and demo tools just slip off it.

Yes, i could rent a bobcat with a jackhammer and just rip out the whole mess but I don;t think it;s necessary. We've cleaned all the holes down at least 10 inches. I can set the posts in that far, pour some hydraulic cement around them to give me another 3-4 inches of burial, and then if need be I can use hd joist hangers to anchor the posts to the slab. Plus the joists, which will be resting on the concrete slab, will be bolted to the posts, so I expect the fence will be plenty stable.

But -- is there some trick I haven;t thought of for cleaning intact wood out of holes in concrete? Could I maybe burn the wood out somehow? Any suggestions much appreciatedl but feel free to just chuckle.

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Old 05-03-2009, 10:19 PM   #2
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Re-using post holes in concrete


rent an electric jackhammer ( bosch brute ) & rip out the conc,,, place the new p/t'd posts in crush'd stone, not conc.

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Old 05-04-2009, 06:39 AM   #3
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Re-using post holes in concrete


Thanks but no thanks. As I said, the concrete is 24" thick with a 4" layer of asphalt driveway on top of that. I already said I don't think I need or want to go the Bobcat route; I'm certainly not going to try to do it with a jackhammer.

In any case, given how quickly people respond with good ideas on this forum, I think I can assume I haven;t missed any easy solutions. So I got my answer, even if it wasn;t what I was hoping for. And maybe I gave some people some chuckles.
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Old 05-04-2009, 07:21 AM   #4
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Re-using post holes in concrete


i wouldn't give up yet.... more info is needed though.
is it... 2 inches or so of asphalt, then dirt, then concrete 24" down as a footing? or was the pole sunk in 'crete all the way down?
in either case, removing a small area of asphalt around the pole, digging it out and then replacing with new posts seems to me to be the best
route so far.
then all you need is some asphalt repair and touch up the surface. there are likely other ways to go too.
if it's a square hole of 'crete all the way down under the asphalt, a different approach may be needed.

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Old 05-04-2009, 07:46 AM   #5
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Re-using post holes in concrete


Danger -- Yup, it's concrete 24 inches down.

But I know my description isn't very clear. Ok - the holes are on a line between the asphalt driveway and a concrete slab that extends about 6 - 10 ft to the house. So on the house side we have concrete slab, then gravel, then dirt. On the asphalt side it looks like there's just dirt or maybe gravel and dirt underneath.

Each place there's a hole somebody poured 24" deep concrete around the posts. I'd guess this was done by digging a hole for the post, then backfilling with concrete but the holes were big - at least 2 ft across. Probably the slab was poured after the posts were in place.

We can't just relocate the posts because most of them are in exactly the places they need to be. An end where the slab butts up against a corner of the house. Another two posts exactly where the gate most logically goes. A couple more at angles in the slab. So there are at most 4 (of 12) that could be moved. Still have to cut back the asphalt and probably the slab to do that.

To add to the chuckle, they poured the slab up against an untreated 6x6 sill beam. The next door neighbor remembers telling them the beam would rot out in a few years. Turns out it took a little longer than that - about 15, and some of it could still be removed in 2-ft pieces. The rest I shoveled out. Thank god it has a full basement. -- Phil
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Old 05-04-2009, 07:56 AM   #6
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Re-using post holes in concrete


then.... if you have a vertical, square 'cave' of concrete to set a new pole into, i think you'd be ok going down 10 or so inches?
sounds to me as it's be strong enough. try to drill/gouge/dig out as much more as you can, of course, but i'd be comfortable if it's a 24" pad.
10 or 12 inches down ain't gonna tip over..... be SURE to order FOUNDATION GRADE FOR GROUND CONTACT 4x4s to replace the rotted ones.
simply 'pressure treated' is not sufficient for your project. +...you won't have the same problem again.

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Old 05-04-2009, 08:05 AM   #7
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Re-using post holes in concrete


If you don't go to the bottom of the hole it would not surprise me if those post continued to sink as the old post rotted out. You would probably be better off fillilng the old holes with concrete and put the post on top with a metal fastener. If the old concrete is a big and deep as you say it will make a good footing.
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Old 05-04-2009, 08:05 AM   #8
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Re-using post holes in concrete


just had a thunk here.... go buy a 2 ft. hunk of threaded rod..... grind a point on one end.... thread on a couple nuts to grip on at other end....hammer it down into the center of the wood, then visegrip and turn it down into the wood. then block and lever to pull it out.
might do it if not too rotted?

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Old 05-04-2009, 08:15 AM   #9
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Re-using post holes in concrete


DM - Been there. Had a 10 x 1/2" lag bolt sitting around. Got it in about 6 inches. When I finally got enough leverage, it just pulled out.

Ugh, I know there are two grades of pt but didn't think about it. Thanks.

Joed -- Good point, I think I'll do that at least on some. But I think I'm going to anchor the posts to the slab regardless, either with joist hangers and/or the joists, so the posts aren't going anywhere regardless.
Thanks all.

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