Breaking up a concrete pad in my backyard. Any advice?

November 28, 2005 2:52 PM

I need some advice on how to best break up a seemingly indestructible concrete slab in my backyard. It is about 8 feet by 4 feet by 2 feet deep. I've tried a sledge hammer and also a relatively low-power jackhammer, with little success.

It isn't actually 2 feet deep, but is 2 1 foot slabs, basically on top of one another. I can't tell if they are connected in some way. The top slab is pretty smooth, while the bottom slab is sort of pock-marked and seems like it would be easier to break (if I could ever get to it). Any advice appreciated.

posted by krudiger to home & garden (22 comments total)

Other than a higher-powered jackhammer?

Is it cold where you are? You could drill some holes, fill them with water, and let nature take it's course.

If that's too long to wait, drill a bunch of holes, then break the slab apart with your jackhammer.

You could also probably rent a concrete saw from a home improvement type place in your area, that would probably be the quickest solution.
posted by madajb at 2:58 PM on November 28, 2005

Can you drill holes in it? If you can, you could try something like this, which is supposed to expand and fracture the concrete. Never used it myself, but it looks cool
posted by true at 2:59 PM on November 28, 2005

Thermite.

Fun and entertaining.
posted by PurplePorpoise at 3:17 PM on November 28, 2005

Concrete is very strong in compression, much less so in shear strength. Accordingly, you need to impose shear forces on it. Drill, or sledgehammer + chisel, not just sledge. Suggest you drill holes in it to perforate a chunk - like a graham cracker - then break it off with sledging. Or fill holes with water, that'll work too. Or fill holes with dynamite, like the pros do.

You could also rent a concrete saw (looks like an overgrown circular saw, pours water on the blade during the cutting to keep it cool). With that much to cut, perhaps the rental is the best bet.

Let us know how the escape goes! Do you have a plan for getting past the sharks in San Francisco Bay?
posted by jellicle at 3:37 PM on November 28, 2005

A concrete handheld wallsaw doesn't cut much deeper than 400mm -- and that's on a wall, with cuts of 200mm deep on each side. A floorsaw can cut up to 300mm deep. You may be better to hire a professional concrete cutting firm to come out. They will either cut it into smaller chunks and break it down with a Kango (a type of jackhammer) or recommend a small excavator with a breaker head (a very strong type of jackhammer that attaches to an excavator boom). At 600mm deep, it's going to be very time-consuming.

If there are two separate slabs you may be able to get away with a floorsaw, though. You need to find out -- the best way would be to get a concrete core driller to come out (or hire the machine yourself, but they're tricky to use) and drill right through. He'll extract the core and you can see if there are one or two pieces.

You may also want to consider where you're going to dump the hardfill, if you haven't already.

I ran a concrete-cutting/demolition company (the admin side) for three years until 1999, and had some hands-on experience as well as pricing and planning jobs. Technology may have changed since then, and there may be more high-power tools or bigger, deeper-cutting saws, but I doubt it.
posted by tracicle at 3:58 PM on November 28, 2005

I saw some guys busting up concrete that thick (and thicker) with a jack hammer mounted on the front of a bobcat loader (it replaced the bucket). It'll cost you to hire someone with one of these rigs, but they'll also be able to load the rubble and haul it off.
posted by 445supermag at 4:16 PM on November 28, 2005

Can you raise them up on something? enough to create a slope... then concentrate on the 'breakpoint'. If you are trying to break them whilst flat you'll be there for days.

Even a slight angle is enough, if you can jack it up and wedge a metal rod in - worked for me once, on a similar sized piece of concrete.
posted by snowgoon at 4:16 PM on November 28, 2005

I can't imagine anyone building a solid 2-foot thick slab. I suspect that only the perimeter is that thick to provide a footing below the frost line. The center of the slab may only be 6 inches. You might try drilling or jackhammering in the center which would allow you to work outward to the perimeter.
posted by JackFlash at 4:17 PM on November 28, 2005

krudiger, do you, by chance, live in San Francisco? I've got a friend in a similar situation with a backyard of concrete and no clue how to get it out of there. Do let us know how it goes...
posted by shoepal at 4:26 PM on November 28, 2005

I've broken up many slabs. snowgoon's right; you need to prop it up in the middle and hit the edges. Let gravity work with you. Concrete's very brittle. Think of it this way: instead of trying to smash a crunch bar into the top of your kitchen table, try snapping off parts over the edge of the table.
posted by glibhamdreck at 4:32 PM on November 28, 2005

Thanks, everyone.

Not surprisingly, I'm trying to do this on the cheap. Some of those rental ideas sound good and I'm definitely looking into the dexpan.

I don't live in SF. LA, actually. I'll let you know what we end up doing and how it goes.
posted by krudiger at 4:38 PM on November 28, 2005

Re: propping it up, I've tried in vain with a iron bar we have, but it is just too heavy - i can't even begin to make it move. I'd appreciate any suggestions on how to prop it up.
posted by krudiger at 4:43 PM on November 28, 2005

krudiger writes "Re: propping it up, I've tried in vain with a iron bar we have, but it is just too heavy - i can't even begin to make it move. I'd appreciate any suggestions on how to prop it up."

Dig under end. Fracture off end. Repeat.
posted by orthogonality at 4:52 PM on November 28, 2005

Having broken up a bunch of concrete myself, drilling is the easiest way to go. I let water sit for a few months, but you could use some product that expands to make the process faster. Be prepared for some nasty, heavy work, and make sure to wear appropriate eye and hand protection.

I live in LA as well, and one of the crappy things about having such great weather is that your concrete is sure to be in great shape.
posted by gregariousrecluse at 5:02 PM on November 28, 2005

In LA, eh? That does away with my idea: drill holes, fill with water, cap off the holes. Let nature do some work.

If you rent, check out the Bosch concrete drill. They have a diamond-tipped bit that the shop will micrometer-measure, then charge you for the wear-and-tear. Slices through concrete like a redhot knife through butter. Expensive but oh-so-easy.
posted by five fresh fish at 5:06 PM on November 28, 2005

I had one of these. Concrete slab, about 12-18" thick .

I got rid of it with a pickaxe, and a lot of patience. The worst part were the 2 foot thick "balls" of concrete where they'd conveniently poured it extra thick. If yours is like mine, it was quite a bit thinner towards the middle, which was a pleasant surprise.

If you don't enjoy sysyphean tasks that involve getting pelted with small concrete shards, I'd suggest hiring somebody.
posted by I Love Tacos at 5:11 PM on November 28, 2005

dig a hole and run water under it over night to displace the dirt and create a cavity, instead of trying to lift it.
posted by snsranch at 5:15 PM on November 28, 2005

Oh, my other major tool was a 6' iron spud bar.
posted by I Love Tacos at 5:17 PM on November 28, 2005

If you still want to do the expansion trick, don't let the weather stop you!

You could buy some dry ice (it's about $2 a pound) and drop it in the water filled holes...

Didn't the ancient egyptians supposedly do this with wood pegs that would expand a lot after being exposed to water?
posted by phrontist at 8:47 PM on November 28, 2005

snsranch: Brilliant.
posted by phrontist at 8:48 PM on November 28, 2005

Large limestone blocks are split using the the stone equivalent of a maul and a steel lining to reduce the friction of the maul against the stone. The technical name of these two tools I don't remember at the moment.

If you want to split the concrete slab, you will have to drill 1/4 -1/2 inch holes every foot to foot and a half. If the slab is one foot thick, the holes have to be six inches deep. Once the holes are drilled start tapping in an iron spike or very big nail, that is just slightly larger than the diameter of the hole, into the hole. Strike the left one, the the center one, then the right one and repeat the process until the slab splits. Each strike will only move the nails a small amount but the combined pressure they apply to the slab will split it.

Most people don't have a drill capable of making such a large hole in concrete but some of the larger hardware stores rent them and will show you how to use them.
posted by 517 at 9:26 PM on November 28, 2005

There are a bunch of different ways to demolish your slab, the best method for you depends on what your goals are.

1. Do you want it done quickly? If so, I'd go with a jackhammer and compressor. Sunbelt Rentals can provide both. They may even deliver it for you.

2. Do you want it done cheaply? Well, there aren't too many cheap ways to do it. Drilling holes and using a sledge and a pin will work, but you'll still need to rent the drill. If you're going to rent the drill, I'd go with the Dexpan expanding mortar. It's pretty cool stuff. Dexpan expanding mortar works extremely well, we're using it on one of the construction projects I'm working on right now to fracture rock. As an aside, the rock is about 10,000 psi, your concrete is probably around 3,000 psi.

3. Do you want to play with construction equipment? Get a bobcat loader and a breaker attachment, again from Sunbelt or your local rental place. It'll make short work of it, but will be more expensive than a compressor and jackhammer.

Two other things you'll have to worry about:

1. Disposal. If your measurements are accurate, you'll have 3.5 tons of concrete on your hands. You'll need to pay someone to haul it away or take it to a landfill or a concrete recycler.

2. Reinforcing steel. It'll be either wire mesh or reinforcing bars. Not much of an issue if you go with the bobcat loader, but if you go with any of the other options, you'll need a pair of boltcutters. Hopefully they didn't put anything too big in there, but you never know.
posted by electroboy at 9:57 AM on November 29, 2005