Excavator question

[Jetboy]

I'm nearing the "fun" of tearing out my old garage to build a new one. It's detached and has a mono-slab.

I'm on the fence between renting a midsized or mini-excavator and tearing it out myself and loading in a roll off, or hiring an excavation company to come do it.

Anyone ever broken out concrete before and if so how big of an excavator do I need for the job? I don't want to spend a week doing it - the slab is only 22'x22'. Is a mini or midsize excavator up to the task? If not I should just hire a pro to come with a bigger machine.

I don't know what is in the slab, maybe some rebar, maybe not. The quality of the garage was that of a handy homeowner who didn't have a f'n clue about building a garage. So there's a good chance there's no bar in the slab, but who knows.

I live 4 blocks from an equipment rental place, so it's pretty easy for me to get equipment to my house. The biggest excavator I could get would be a Terex TC60 which is about 12,000lbs/44hp, or a backhoe similar to a case 580 in size. Not sure if either are enough for the job.

Oh, and if you happen to know a reliable excavation company in the Salt Lake City area, I'm open to suggestions.

 

[PAToyota]

The local rental place has Bobcat equipment. A 323 (smallest - 1032lb lift capacity) rents for about $600 for a week while an E80 (largest - 9325lb lift capacity) is $1000 for a week. For the $400 difference, I'd rent as big as I could fit (the 323 is just over 3' wide while the E80 is over 7.5' wide). Couldn't find specifications on the T60, but it looks like about the same size as an E55 or E60. You should be able to tear things apart with something that size.

Whether the slab is reinforced is going to make a huge difference. I've broken up unreinforced concrete just by lifting and edge and then smacking the chunks into smaller pieces. Just a matter of getting something under them to create a stress point.

The other question is whether you have the means and a place to haul the debris off to? Tearing it up is only half the battle - then you have to load it up and take it somewhere.

 

[Photoman]

If the slab is 4 inches thick, which I doubt from your description of the previous owner, then you are talking around 13 tons of concrete. Check with the roll off company and find out what their limits are weight wise. It might take more than one roll off. An excavation company should have their own trucks and this would not even be close to a tandem load weight wise. Costs can then be checked either way. Some guys with aluminum dump beds don't like concrete or rock work but they can just put a couple of buckets of dirt in first if they are really looking for a job.
A 580 Case would eat that slab up. A decent operator could have it done in 2-3 hours. Check the controls as Case machines can come with different ones. A thumb makes it real easy; a 4 in 1 on the front can pick up larger pieces. With either an excavator or a backhoe it just takes a start in concrete. The slab can then just be lifted and will crack and break. It is easier to dig in concrete once you get a start than it is to dig in frozen ground. To make smaller pieces just put the edge of one piece of concrete on another and give it a tap with the bucket teeth. Steel should be no problem in a residential slab. In fact many times you can hook a tooth in the steel and load a couple of pieces of concrete.

 

[Joe_E]

A mid sized or double ender is fine if it is 4".
Little tough for a mini because you have to be able to safely load the can without dropping s*** in your lap.

Work your way from a corner. If there is no rebar or wire you can fly through a 4" slab. Just lift big pieces and drop them, they'll crack into smaller.
Thumb would be ideal for leaving all your subbase material and just picking up the concrete.
Park the dumpster near the slab and start on the far side and keep swinging the broken slab towards the can on the pad. That way when you can load the can from one pile and rip up the slab under the pile when you have the rest loaded.

 

[Jetboy]

Thanks for all the advice. I'll have to get some estimates from a couple excavation companies to see how much the cost difference would be and go from there.

 

[se2000]

Do you need to remove the old slab? Maybe as my brother did was to build an new footing around it and poured 2" over the old and new.
If you do go with removing, I'd go with a 4 or 5 ton unit. You could do it in a day, just make sure you have enough dumpster available while you have the machine. You don't want to pay an extra day or have to load by hand.

 

[Delancy]

Do you need to remove the old slab? Maybe as my brother did was to build an new footing around it and poured 2" over the old and new.

What I would suggest, except 4" cap on top of 4" of screenings, or whatever compacted fill.

 

[Jetboy]

The roll off companies that will take concrete charge $300 per roll off, and I'd need two separate dumpsters for this much. Plus I need a third for the garage building. I could cut up the garage by hand pretty easily and load it the weekend before. And I think I could do the tear our and loading in a day, plus the dirt work necessary for the new slab. Then I'll need to find some washed rock.

I'm thinking by the time I spend $900 on 3 roll offs, plus $600ish for a day's equipment rental or $1200 for two day's equipment rental, I'll end up cheaper to have an excavation company come do it. I had two companies come out and they're going to give me prices. I suspect it will be cheaper or close to doing it myself and a lot easier. Hauling off the old concrete is really the expensive part and I'm guessing a dump truck is a more efficient way of doing it as compared to loading roll offs.

 

[Jetboy]

The new building will end up being a foot to the side of where the current one sits (zoning issues ). So I'd end up having to cut off at least two feet off one side of the existing slab. I'd love to just re-use the slab, but after digging around it, it's a 4"ish slab set on dirt. No footings, no washed rock under it. I don't think it's a very stable base to build on.

 

[Cookiemonster]

Even if its a 6" reinforced concrete slab any 12k machine with a breaker will do the trick. A 22'x20' slab shouldn't take you more than 2-3 days at the most. A CAT 305 which is right at 10k would work. I speak from experience. Unless your hitting some crazy 6k-8k lb concrete mix it should go fairly quickly. Grinder or torch to cut the rebar if any. As far as disposal if you have the property I'd dig a nice big fat hole and drop it in then back fill it and regrade, expect some settling over the next few winters though with a final regrade in a year or two if needed.

 

[Jetboy]

I ended up with a cat 303.5 IIRC. Worked great. Slab had no metal in it and was only 4" thick or less. Entire thing was gone in about 3 hours. No breaker. Just lifting and breaking out sections and hauling to the dump bin. With a dump truck or trailer closer I could probably have cut that time in half. The only issue I had was some of the bigger pieces were too much for it to lift over the edge of the bin. It could carry them to the bin, but wasn't strong enough to get them up to full height. A couple roughly 6x6 foot sections I had to drop and break up to get in the bin.

It was a great machine to use. Nice and easy. I rented an asv (Terex branded) skid steer later to do some other dirt moving around and wow - what a difficult to operate POS. It had 30hrs on it - practically brand new and it would stall (kill the engine) regularly trying to turn if there was any minor obstruction. If nothing else it should have a hydro bypass valve to keep the engine from dying. That was only one of many issues with it.

I used the mini ex to dig my foundation too. It was ridiculous due to government requirements. 36" deep 24" wide footer full or rebar. I pity the fool who has to remove that some day. It's going to require something a LOT bigger to take out. I suspect the entire slab might be moveable in one piece now... I also know it won't be me doing it.