Introduction
During my time, there have been a few times I’ve run into a sunken concrete slab. There might be some specific reasons why it has happened, maybe the soil wasn’t compacted well enough, freeze-thaw happened or water has been eating the ground beneath it.
I like to say that reason isn’t that important when the damage is done – it’s best to get it under control before thinking that. So let us have a look at concrete raising in this article.
There is one article about mudjacking vs. polyjacking on this site, but it was more about comparing the two. I want to concentrate more on the process and how it works for this one. I guess the first question would be does concrete raising work?
Indeed it does and it has been working for something like 100 years already. It’s not a permanent solution, but the results last several years.
That would mean that if you have a slab in the second half of its expected life, and if the raising is not that expensive, it could be a better option than replacing the slab. It can be a matter of cost in many ways actually.
Decorative concrete gets more expensive the more complex it is. If you have invested in your slab a lot, it’s more than likely that raising it will be cheaper than getting a newly decorated one that is on the same level.
It could also be a plain old grey slab. Removing and redoing one is heavy work so I don’t judge quick solutions that work out.
So how to raise the concrete slab?
As stated before, the sinking of concrete slabs is most often caused by voids under the slab. These might have been caused by water slowly removing material, ground heaving, or pressure which is also a way to compact soil.
So soil that is not compact and pressure is a bad combination as the thicker the slab is, the more weight the dense concrete has. Sound logical right?
The reason might not matter that much, to get the slab back up you would need something to put under it. Mudjacking vs. polyjacking work in a little bit different ways.
Mudjack concrete raising
Before we talk about mudjacking, it might be good to understand what it is. When mudjacking is done, limestone aggregates with cement are forced under the concrete from holes that are drilled into the slab.
The mix will fill the voids and lift the slab by pressure from the used machine. The concrete lifting machine can be a mudjack pump that will feed the cement lifting mix through the holes drilled.
The concrete lifting can be done by other means as well, but I’d maybe use polyurethane for that kind of lifting method. Hydraulic pumps can lift quite heavy weights, but the problem is getting the cement mix under the slab evenly without a proper pressure tool.
That being said, you also need something to pump polyurethane under the slab. For most people, these are not DIY projects.
So is mudjacking worth it all? I’d say it depends on the slab’s expected age. If you DIY, you need to rent some machines to be able to do it.
The problem might be that proper machines won’t be rented depending on local laws. If it’s not an option, the only way to know is to make some calls and compare prices.
Polyurethane concrete raising
Regarding the DIY department, I think polyfoam concrete lifting might be harder to achieve. That’s because the way it works needs even more special tools than mudjacking.
Raising concrete slab will work pretty much in the same fashion. You need to drill holes for the polyurethane to be injected.
Polyurethane has two components that react with each other when they come together at the concrete hole. This will cause the expansion and lifting of the concrete.
Before injection, you need to lift the slab a little, hopefully to the correct height. After that, the polyurethane is injected and will expand and fill the voids under the slab.
It will expand and set very fast so if the slab is lifted to the correct height, the extra will come off under it and set in under half a minute. You can drive a car on it on the same day so it’s a lot faster than mudjacking that needs curing time.
The advantage of this method is that the foam is very light, it won’t add more weight to the ground so it won’t cause extra sinking because of that at least.
How much does it cost to have concrete raised?
Now this question changes from place to place and you will have to call your local contractors. Things that affect the price are the local pay rates for workers, the price of materials, and the size of the slabs being raised.
For mudjacking the price should be around 5$ per square foot. Might be more or less depending on where you live. So if you have 10 feet wide driveway that is 20 feet long the cost would be 10*20*5$ which amounts to 1000$ in our imaginary case.
For polyjacking the price per square foot is probably more, maybe up from 10$ per square foot.
Here is an easy trick you can do if your contractors don’t want to tell you the price. Ask multiple contractors for the cost of the job, and skip the ones who doesn’t want to give you that. They are more than likely the ones who want to overprice their work.
Divide how much it would cost you by the number of square feet of your driveway/slab and you will have your price per square foot. For example, if the contractor gives me a 1500$ estimation, I’ll divide it by 200 square feet (10*20 of my example) and know the price is 7,5$ per square foot.
DIY concrete raising for those who like to get their hands dirty
To keep it simple, I will assume that raising the concrete would be done by cement mix or using soil. Both are something that anyone of us should be able to get.
For concrete leveling DIY work, you need to be a little resourceful as lifting the concrete can be tricky. You can use hydraulic pumps, but getting the lifting force on both sides of the sidewalk, for example, can be hard and you might need to build a tool for it yourself.
With enough leverage everything is possible and one way is to use heavy construction equipment like excavators. Depending on where you live.
Sidewalk
Something like a sidewalk you might be able to fix by using soil if it’s not too wide. The wider it gets the harder it will be to lift and fill under. Concrete gets heavy quite fast when the object gets larger.
That being said, you need a way to lift the sunken end. If there is more than 1 edge, it gets even more complicated as you will have to lift it 1 end at a time or both at once.
Whichever way you choose it will be hard work. Depending on the size of the concrete, you can use either leverage or you can dig and use something like a car hydraulic jack if working by hand. Just make sure it can handle the weight.
At this point, you might realize that a hydraulic jack might be hard to use in that kind of condition so you might want to invent some helping tool that can handle the weight of the concrete, is easy to place under the slab, and is easy to lift with it.
When you get the piece of concrete lifted, you need to fill it under it with soil. It’s hard to get it there compact enough, but it can serve as a temporary solution or it might last surprisingly long before sinking with rain and such again.
Mudjack at home
Before even beginning, I think that correct concrete raising should be done with professional mudjack equipment. It’s hard to come by with alternatives that can get enough pressure for it to work like it’s supposed to.
One way I can think of is lifting the slab slightly higher than necessary. That way if you can fill the void when you let it down the pressure will fill the voids beneath the slab.
If the slab is small, this might be manageable, but the bigger it is the more unlikely it is to succeed. That’s why I’d rather call in people with professional tools.
The main reason for that is that without proper equipment, it’s hard to get enough cement mix under the slab from any hole that is made. Small lift and homemade pressure tools might get enough “mudjack” under the slab, but the wider and longer it gets you might end up needing buckets upon buckets that need to be poured underneath.
But if we deem the job manageable then first, big enough holes should be drilled as mentioned before, from the sunken end towards the end where it’s not. Or if the whole slab has sunken, it would need lifting all around.
When the holes are drilled, the mudjack pump pumps cement mix into the hole and under the slab. It will start lifting from the sunken end.
When it’s at the correct height, you move to the next hole and fill it up as much as there is free space. Work like this until you are at the other end.
Conclusion
I hope this makes sense in concrete raising and how it is done with different methods. After some thinking, I included the DIY concrete raising, but I honestly think it will likely be a waste of money and time to do it yourself.
The equipment rent will cost, your time is also valuable, and the professionals should be able to do it well enough for it to last longer. If not done well, it could even be harder to fix in the future.
I know some people can handle it more than well, but it might be a waste of time for most.
The main thing I’m concerned about in a job like this is that the fix won’t get under the slab well enough. As said before, there are multiple reasons for concrete to sink and it’s more than likely to do that with time.
If it’s not done properly it might just be the same situation next year or even worse. But when it comes to concrete raising, I think it’s a worthy try with expensive concrete slabs and why not cheaper ones depending on the price tag?
