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I'm replacing a fence post which was a 4 by 4 with concrete poured around it. I have been trying to break up the concrete with a sledgehammer, which works okay but it is slow going.

Is it workable to use a wedge for splitting wood for the purpose of splitting or breaking the concrete? It seems like it should be okay but I wouldn't want to run into some problem I didn't foresee. For example, maybe it would dull the edge too much -- is that an issue to watch out for?

I know there are wedges that are specifically for splitting stones or concrete but I am hoping I can just use the wood splitting wedge which I have already.

EDIT: It turns out I have a masonry chisel in the basement. Similar question -- is it workable to use a masonry chisel to break up the concrete in a post hole?

SECOND EDIT: There are a lot of great ideas in the answers below. About the specific question about using a wood splitting wedge, looks like the answer is NO.

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  • My brother used splitting wedges to split a 4’ granite bolder on his property, he drilled a line of holes then used 3 wedges driving 1 then the other until it split then it was light enough to move with his tractor, doing the same with concrete should be much easier. I have had luck with 3 4x4s used with a cable winch 2 loops around the top and they pulled right out (I could not get my tractor in there and popped them right out.
    – Ed Beal
    Jul 5 at 1:49
  • A few youtube vids about splitting large rocks like that. Who needs a gym with that job.
    – crip659
    Jul 5 at 2:58
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    I definitely wouldn't try using a wood wedge for concrete. Likely wouldn't cause issues, but you run the risk of it being designed for softer material and splintering with a hammer. My grandfather got 'shot' in the gut by a rogue piece of a bolt that splintered and I've been wary of the possibility of splintering metal ever since. Jul 5 at 14:48

6 Answers 6

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When confronted with this I have just drilled / pulled out the old wood from the concrete and inserted the new post into the hole. Easier than breaking up the concrete and then repouring fresh.

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Masonry will help but not so much without pre-drill.

Get a hammer drill and good concrete drill and weaken the concrete by drilling holes.

That will also tell you how deep the concrete goes.

Mechanics, since the concrete sits on soft soil, the sledge hammer would just bounce off with minimal damage to the concrete.

Since the concrete was poured around the post, it is possible the concrete goes up to 3 feet deep.

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Easy option:

Keep the concrete in place and get a fence post support that goes in it. Could be one with 4 screws (one in each side) or one like that:

enter image description here

Hard option:

Is it workable to use a wedge for splitting wood

Yes, if you make a line of holes using a rotary hammer, then put the wedge in and smash it with the sledgehammer, the concrete block should break. But you need to pre-drill it and make a space to slide in the wedge, so it... uh, well, wedges the concrete and splits it. Otherwise of you try to bash it in, it will just bounce off.

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If you really need to get out the old concrete:

Option 1

I'd go for a rotary hammer (not entirely sure I got the right translation, in German we call it "Boschhammer", they are machines the size in between a drill with hammer mode and a jackhammer. You want one with hammer-only mode and a concrete chisel bit.

(If you can actually achieve progress with only the sledge hammer on a concrete block inside a hole, that does not sound like very hard concrete)

Option 2

If you have access only to a power drill with hammer-drill mode (no hammer-only), you can also drill rows of holes, get out the stuff in between with the manual chisel or a crow bar, and then pry pieces apart with a crowbar or digging bar.

Over here, we locally make a serious version of crow bar/digging bar by welding the head of a pickaxe lengthwise into a steel fence post. That gives better impact inside the hole (where you cannot use the pickaxe), and also a good lever.

Option 3

digging bar, possibly with the aid of a pick axe at the beginning and later your masonry chisel


wood splitting wedge

No good option IMHO.

It's not going to be very efficient for breaking up the concrete, plus you'll have a whole lot of work putting it into working condition for its actual purpose again.

Plus: A hard (steel) wedge in concrete means a substantial risk of the wedge jumping out of the slit/crack when you hit it, but the impact is insufficient to crack the concrete. (This is also why soft wedges like the aluminum and plastic ones are nowadays recommended for wood, both for splitting and felling). At the very least remember not to hit steel on steel.

 For example, maybe it would dull the edge too much -- is that an issue to watch out for?

From the point of view of achiving your goal to destroy the concrete, it won't get duller than using the sledge hammer directly...

Wedges for wood come in very different types. Many will be far too soft for working on concrete (e.g. the aluminium plus wooden back ones).

is it workable to use a masonry chisel to break up the concrete in a post hole?

since the description of your concrete doesn't sound very hard, that's certainly an option. Depending on the size of the chisel (an electrician's chisel won't be fun...) likely much better than the wood wedge.

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  • By "rotary hammer" / "Boschhammer", I think you mean "an SDS drill". Jul 5 at 11:14
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    @MartinBonnersupportsMonica Rotary hammer is the correct term/type, they do often come with SDS+ chucks but not always.
    – Bob
    Jul 5 at 13:17
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    I like "Boschhammer", I think I'll start using that! Since Bosch is a large manufacturer of rotary hammers and (AFIK) invented the SDS chuck, it's very similar to the way Americans use the term "Sawzall" which is a trademarked name of Milwaukee Tool Co. as a generic term for all reciprocating saws commonly used for demolition work. TL;DR: Yes, you've used the term "rotary hammer" correctly.
    – FreeMan
    Jul 5 at 13:33
  • You are right of course @bob, but in reality, SDS is what most people call it. Jul 5 at 13:37
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Keep the post in the concrete and use the post as a lever to help you remove the post with the concrete in one go.

Once the concrete and post are out a sledge will easily remove the concrete from the post should you need to remove it prior to disposal.

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  • Pouring water in the hole should help with the cement to slip up some. Will probably need long jacks(rental) or make some type of lever to lift. It is very nice to have a tractor with a loader for this job
    – crip659
    Jul 4 at 23:41
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    The OP is "replacing the post". Normally the reason for replacing a fence post is that it has rotted and snapped. Normally it will rot around ground level (where both water and air are available to the fungus that digests the wood). This means that there is almost never a lever available. If one has a stout steel bar available, drilling a hole and then driving it in might give the OP a lever. Jul 5 at 7:03
  • true it would be the most common but if it snapped at that point you'd be looking at digging out the concrete or adjusting your fence layout so you don't have to dig it out - not splitting the concrete from the fence post. Jul 5 at 7:51
  • Much easier if you can split it out, rather than making the new hole much bigger by digging it out - it's what I have done in the past. Jul 5 at 11:09
  • @MartinBonnersupportsMonica, I'd just chuck a sonotube into the hole and backfill. I do like the metal U post supports if repouring concrete so you can easily replace the post when it does fail. I haven't tried splitting though I just can't imagine that to be quick or fun - I have split bolders with feathers and wedges but generally the pieces have somewhere to go... how do you split the concrete when surrounded by soil? Jul 5 at 17:44
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IMO, your best bet is to find a way to pull out the post with the concrete intact. Then replace the post in the hole and either refill with new concrete or to pack in some fill dirt.

There are various ways to pull out the post. One way is by using a front loader, a backhoe, a forklift, or something else to pull it straight up. I've seen some videos online about using a car tire/rim and a log chain/tow cable attached to a vehicle in order to pull a tree stump. The idea with the tire is that you put the chain as close to the ground as possible and the tire redirects the horizontal pull into a vertical pull.

Once you get the post and concrete out of the ground, you can dispose of it, without having to break up the concrete, in a dumpster or by taking it to the local landfill yourself. And if you need to make it smaller, you can cut the post easily enough, or if you do need to still break up the concrete, it's much easier to deal with. You can even use a tile or concrete saw at this point, even if it's just to make stress points, like other people were suggesting to use the drill holes, which could still be done.

I would recommend against using a log splitter wedge. They are sharp because they are designed to get in between fibers or to cut across wood fibers. Rock and concrete, not so much. If you look at a new masonry bit, you'll see that it's not sharp at all. It's not cutting, but rather chipping away the material, which is why electric drills for masonry and concrete have a hammer action. You can drill through masonry and concrete without the hammering, but it'll burn up bits really quickly. Been there, done that.

Most likely, you'll dull the wood wedge in the first few blows and end up breaking off chips, so it won't even be good for wood cutting anymore (at least not without significant grinding it back to shape). If you keep using it, those chips will lead to stress cracks which could lead to large pieces breaking off at high speed, or simply just crack the wedge in half.

You can even get wedge or spade bits (also not sharp) for hammer drills/rotary hammers that are designed to use only the hammer action, not the rotary action, so it's more of a small version of a jack hammer used in road construction.

What you need to break up the concrete is shear stress, where one part of it is stable and doesn't move while another part isn't supported. Often times, this is done by the large size of the slab of concrete it's poured as, but you don't have a slab, but a column, so that's more difficult, and it has a soft core of wood to help absorb vibrations. About the only way this is going to break up is of you have a slab of concrete that you don't really care too much about or is really thick, lay the post on the slab, then support only one side, then whack at it with the sledge hammer until either you or it gives up.

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