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Raise Sunken Concrete?


Hello. I have a 5x5 concrete porch that has sunk 6-8 inches. The porch consists of a top surface with an 18 inch skirt, and a step. I believe it was a single pour.  The porch itself is in good condition, so I am seeking methods of raising it. I have looked into slabjacking, and pressure-fill lifting, but was actually looking for a pneumatic solution. any thoughts, comments, anecdotes, would be greatly appreciated. Thanks

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abenjam54 years ago
Does anyone know of a place where I can learn more about concrete pumping in Calgary? My neighbor suggested I have it done, but I don't know what it is.
trschroeder5 years ago
Build a 2x form. You want the finished slab to be 4" - 6" above the adjacent grade. Provide 6"-8" of gravel fill over the existing slab. Pull some of the gravel away from the form, providing for a dropped concrete edge, 8" wide, tapered up to the main portion of the slab. Use slab reinforcing mesh, 6x6 or similar. Pour a 4" slab. I'm not getting the 18" skirt, but am thinking the concrete deck is, or was, 18" above the adjacent grade. If that's the case, forget my second sentence. Not knowing where the steps are, you may have to top the tread. Use a minimum of 4" cover. I suggest 7" rise and about 12" treads.
tewharau5 years ago
Why not just box around it & lay an 8 inch slab on top? If you don't like the concrete layered look on the edge, tile the top & sides. Hope this helps.
sgunkler (author)  tewharau5 years ago
I think the added weight would accelerate the problem. However this plays out the porch will need appropriate foundation. This is my sisters house, and I have suggested casting one extra step, or a deck-over, but she wants it to be as it was originally. Thanks for your reply
It could sink further but if it has taken 10 years to sink 8 inches, it may take another 10?

If it has sunk 8 inches in 6 months, I'd be pulling it up, and digging down to solid. Put in a ring foundation or cinder blocks, fill with clean gravel and the old concrete, and lay another slab.

Hope this helps.
If its now twice as heavy, it will either sink twice as fast, or, if you exceed the yieldstress of the soil, right away.
orksecurity5 years ago
I've got a sunken area in my basement floor, where presumably there's been some settling (I hope not erosion). I asked a contractor whether it would be worth trying to do something like pump more concrete under it. His advice was not to touch it.

Something to check: Has the porch actually sunk, or has loam built up around it? Depending on how you're caring for the lawn, and how long it's been, 6 inches of increase in ground level isn't impossible. If it has tilted this obviously isn't the case; if it's still level you might want to attack the problem the other way around by re-grading the yard.
sgunkler (author)  orksecurity5 years ago
The porch has left an impression/material on the front of the house where it used to be. It does seem to have actually sunk into the ground about 6-8 inches. The porch is curiously level . it seems to be a common problem in the neighborhood. I don't think any footers/foundation was put down - just cast on the bare ground. thanks for your reply.
rickharris5 years ago
In the long run it might just be easier to brake it up and relay - It sank for a reason that you will have to fix.
If you are going to spend the money, do it 1 time and be done.
sgunkler (author)  rickharris5 years ago
every porch in the neighborhood suffers from the same problem, they were all cast without foundation (on the cheap), so they rest on their skirts - rain and time have caused them to cut into the ground, runoff doesn't seem to be an issue. After raising it, I'm going to install adequate foundation. Thanks for your comment, knowing all the angles before I start the project helps..
You could shift it on an airbag, at a pinch, but you have to get the bag under the slab somehow. You'd need about 1 PSI in the bag, if you could get half of the area of the slab covered.

Steve
sgunkler (author)  steveastrouk5 years ago
Thanks for the reply. having difficulty locating an airbag, but this seems to be the most efficient/safest way to evenly lift the structure. thanks again.
Try truck inner tubes ?
sgunkler (author)  steveastrouk5 years ago
Simple, cheap, and so obvious it completely evaded me! brilliant! thanks
sshuggi5 years ago
Be sure to watch out for cracking that slab. If the concrete has any room to sag, it could easily snap or crack. Remember concrete is good in compression, not in tension.
sgunkler (author)  sshuggi5 years ago
Thanks for the reply. Good advice.