Removing large concrete slab to plant trees under

ilovemytrees(5b/6a Western, NY)October 5, 2013


We removed a large building last year from our property. It really opened up our property. Funny enough, it didn't lower our taxes by much, but I digress.

The slab is HUGE. 45ft X 35ft or so.

I know we'll have to haul in a ton of top soil because I want to plant a row of mixed conifers in that spot. I can hardly wait til next spring! Would the area need some fertilization because the land has been covered by concrete for over 60 years, and since it was a garage, had cars sitting on top of it for most of those years? I want the best start for the trees. Unfortunately, we don't own a tractor, so the gravel pit down the road will just dump the soil for us to spread ourselves.

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toronado3800 Zone 6 StLouis(6)

Now THAT is an excuse for a good soil test if I have ever heard one.

And it is going to be a bit of work. At times my riding mower has helped me a bit even if it is hard on the little tractor.

    Bookmark   October 5, 2013 at 1:09PM
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Because the soil under the pad has been covered by concrete for such a long time and also been down by the weight of cars etc., it is probably quite compacted and probably dry. If there was a gravel bed under the slab, make sure it is removed. It would be a good thing to plow or till the soil before and after you get the new soil delivered. Especially after you get the new soil. You do not want a sharp difference in soil types.

Being in Western New York, you should have a good wet winter. I would suggest that you not plant until the spring. This would allow the winter rains/snows to recharge to soil water where the slab was.

As always, dig a $10 hole for a $5 tree.

    Bookmark   October 5, 2013 at 1:09PM
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Not entirely sure from the original post, but I'm assuming the concrete slab is already removed. A soil test is an excellent, even essential, idea.

Not to be discouraging, but a 6" layer of topsoil, according to my rough and perhaps not entirely reliable mental calculation, will require about 25 yards of material. Remove any gravel that was beneath the slab as advised above and you will need far more than 25 yards. I'm not sure what the per yard price of topsoil is in your area, but you are looking at a major expense. You're also looking at a monumental task in spreading even the lower amount by hand.

The best you can hope for is a soil test that shows no contamination from oil or gasoline and reasonable fertility already. This would mean a smaller amount of brought in material and maybe enough of a savings to permit the hiring of equpment and an operator to spread and mix the new with what's already there - including the gravel - rather than having to remove anything.

    Bookmark   October 6, 2013 at 5:50AM
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ilovemytrees(5b/6a Western, NY)

Good morning everyone.

No, the concrete slab has NOT been removed; it's still there. I am very concerned about oil and gas contamination because the previous owners, well the husband, his hobby was being a mechanic, and he was always working on his friends' cars. At any given time there was 6 or 7 cars parked in and around the garage.

In the middle of the concrete slab is a giant hole, I guess to let the oil run down into the ground. :(

The garage was made of cinder block, so all around the concrete floor are two rows of cinder blocks, 16 inches deep. 16 inches I have to fill with top soil. The price is going to be astronomical. I'm aware.

Look, you guys are the experts. If gas and oil went into the ground, am I only looking at grass as a possibility here? Are even bushes a possibility? I have sandy/gravelly soil. It's basically rocks and sand. Does that help?

Edited to add, I don't think there is any gravel underneath the slab. There are some major cracks in it in a few different places, and we can see all the way down. No gravel that we can see. The slab itself is only about 1 and 1/2 inches thick.

This post was edited by ilovemytrees on Sun, Oct 6, 13 at 10:34

    Bookmark   October 6, 2013 at 10:27AM
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jcalhoun(8b Mobile County AL)

Most likely the hole in the slab was for a hydraulic lift for servicing the vehicles.

    Bookmark   October 6, 2013 at 10:56AM
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jcalhoun(8b Mobile County AL)

Also, if you want to remove the slab yourselves an air comprssor and jackhmmer can be rented. You can also rent a construction dumpster to put the broken cement in if you need a way to get rid of it.

    Bookmark   October 6, 2013 at 10:59AM
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ken_adrian Adrian MI cold Z5

yes on soil test ...

but i wouldnt waste money on moving in tons of soil ...

havent we taught you to plant in native soil???

where are you going to buy native soil ????

the only reason to do so.. other than winning the lotto ... would be if you were tending towards a berm.. to escape your flatness ...

in fact .. i might even skip the soil test ... for fear the feds might declare it a toxic area.. and then what.. charge you a million to remove several feet of soil ... what a potential nightmare ...

trees and shrubs are not foo foo .. and you know that already ... and i doubt there is anything he could have done.. to so badly hurt the soil.. that you will have trouble growing stuff ...

crikey.. they are razing an old gas station in town.. and the lot is covered with weed trees and shrubs.. you cant beat these things back with a stick.. and you know that ...

have it removed.. regraded.. and start planting ...


    Bookmark   October 6, 2013 at 11:14AM
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ilovemytrees(5b/6a Western, NY)

If I took a picture of the hole, would you guys be able to tell me if it was a hydraulic hole or one used to drain oil and gas?

We have thought about going the air compressor/jackhammer route with a dumpster. They want $400 for just the dumpster and then charge the dumping of it based on weight. I was hoping to have a guy around here take it and use it for "fill".

Okay, the real reason I want this done is this: Because it was an attached garage there are/were no windows on the lower entire side of the east side of our house. I hate how it looks. It runs along our living room, kitchen etc and I want to plant trees to hide that fact. Our entire first floor is cinderblock (hidden under vinyl siding) so getting windows put in would be a major pain. The neighbors said try the window route and pave the slab and make it a nice patio. But I want a yard there, and to plant trees there and possibly get a window in somewhere.

DH is a little intimidated about doing it himself. He's a suit and tie kind of guy, (I don't mean that pejoratively obviously) and learning to drywall was a big step for he and I, which we did this year. But the jack hammering of such a large slab is something he isn't sure he wants to take on. He's not sure how long it would take, and the safety of doing it ourselves, and since it was an attached garage, the concrete slab abuts our house. We can't tell how complicated THAT would be, getting that close to the foundation.

ETA: Ken, the gravel pit is right down the road; their soil is our native soil. After what you said about the Feds, and this being NY, there is no way I'm going to have a soil test now. lol

This post was edited by ilovemytrees on Sun, Oct 6, 13 at 12:19

    Bookmark   October 6, 2013 at 12:13PM
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I believe you said the garage was a block garage and by inference the concrete was poured on a platform surrounded by a block wall. This could mess with all of the great plans proposed.

As I have seen is this technique for build, the garage floor is significantly above grade. They build the surrounding wall, fill with any thing available to bring the ground surface in the block wall to withing 6" of the top of the block foundation A layer of sand is then spread on this to form a pad for the cement..

If this is the way your garage was constructed, You may have a lot of worthless fill to remove before you can actually find suitable ground for planting.

I would also consider the comment about a hazardous waste site. This could be a very expensive situations, because as owner of the property you are responsible for any contamination coming from the property

As for the hole, are there any small bolt holes near the big hole that would indicate something was bolted to the floor near, around or over the hole (the bolt hole pattern would be very telling.)

    Bookmark   October 6, 2013 at 1:22PM
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Given your description of how the garage and surrounding area were used, it would seem very likely that there is significant contamination of the soil. Whether you have the soil tested to confirm or refute this is really between you and your conscience, but gasoline especially is capable of migrating in unexpected ways particularly when the ground provides good drainage. If you or your neighbors have wells the danger is quite real. At the very least, I'd find out what the relevant laws are in your state. In many cases this kind of pollution, especially if it was not revealed when you purchased the property, is not your sole responsibility and may qualify for various forms of mitigation using public funds.

    Bookmark   October 7, 2013 at 5:42AM
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I was in a similar situation. 40 x 40 slab in my backyard including car path all the way up the side. Take a look at the before and after - 2009 and present:

House was built in the 20's and no idea how long the 6-8" slab was there. Had it jackhammered and hauled away. After that, just tilled everything and got rid of most big stuff from the ash sublayer and mixed the rest in. Might have brought in a few yards of topsoil (because I didn't know what I was doing), and as many buckets of city compost I could haul, but that's it. I'm also big on shredding my leaves in the fall and spreading them back down.

Everything thrives today like the concrete never happened. I should also mention that all plants are native. Ironically, I have a higher planting success rate in the area that was paved than in the front yard, which was never paved. Can't see them from this perspective, but there are another 7 trees, a pond, and a few perennial/shrub beds. I'm phasing the grass out with shredded hardwood since it's the only vegetation I can't support on rainwater alone. Took me about a year to get the rainwater runoff figured out with swales and directing it to appropriate plants, but I have no paved surfaces and no basement water issues.

Congrats on your decision.

Here is a link that might be useful: before and after

This post was edited by c2g on Mon, Oct 7, 13 at 11:49

    Bookmark   October 7, 2013 at 11:45AM
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ilovemytrees(5b/6a Western, NY)


Hi! How long did it take to jackhammer it completely up? How many people were jackhammering it? How many truck loads did it take to haul it away? Thank you so much in advance for answering my questions.

    Bookmark   October 7, 2013 at 5:08PM
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At the risk of being repititous, the concrete is not your main problem. Gasoline and oil in the ground under and around the slab is. Ignoring this issue would, imho, be a very serious mistake that may very well come back to haunt you in the future. Purchasing property without knowing about potentially serious pollution is one thing. Knowing about it and proceeding as if it did not exist is another entirely. Perhaps the previous owners were extremely careful and there is no serious contamination at all. Only a soil test will tell you.

    Bookmark   October 8, 2013 at 5:07AM
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ilovemytrees(5b/6a Western, NY)


The former owner, I found out from my husband, did not fix cars mechanically. He did detailing work only. The whole in the middle of the concrete was to let any rain that got in, to drain down into the ground. It was not used for any hydraulic uses. It's just a simple hole.

    Bookmark   October 8, 2013 at 10:48AM
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@ilovemytrees - I found a guy on craigslist who owned a dumptruck and a jackhammer. To break up the entire 40x40 pad and the driveway that ran the length of the house, I think I paid him about $1800 and amazingly he got everything out in two loads over 3 days with the help of two high school aged kids.

    Bookmark   October 9, 2013 at 1:29PM
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