DIY Garage Slab Leveling

[DustynBeardface]

So I have this garage built in 1962 that was pretty obviously put up by someone's cousin Tony who "knew a thing or two about buildin' stuff". The slab is 6 inches thick in the middle, 3 inches thick on the perimeter. It has a massive grand canyon sized crack running east to west, and a smaller crack running north to south in an almost perfect cross. The whole building is leaning to the north, and it's pretty ugly as well (pictures attached).

Now the correct answer to the question I'm about to ask is "knock it down and start over", but I'm not looking for the correct answer. I have a finite amount of money and time to make this thing a slightly less terrible version of itself, and I'm weighing options to do exactly that.

First project is leveling the slab. I have come up with a few different ways to tackle this and I'm curious what you all might do in my situation. To raise the slab I plan on coring four 8" holes per section (sixteen total) and dropping a bottle jack into each hole. I'll then anchor sections of chain into the slab and cross it over the top of the jack so I can slowly jack the slab section level. I also plan on coring one 8" hole in the center to accomplish phase 2. Once the section is level I have thought of a few options:

1. Hire a concrete company to bring out a truck with rip fill slurry that is basically portland cement and water that will flow under the slab and then harden. I calculated it needing roughly 1.5 yards of material to do the entire building which was quoted at just over $500. If I wanted to do that I would need 16 bottle jacks and a ton of chain to pull it off. I can do it in four pours for an additional $300 which brings the grand total to roughly $800

2. Mix a portland slurry myself and do the pours section by section. This will take roughly 45 bags of portland at $18 a bag equaling around $800 dollars, plus the rental or purchase of a mixer.

3. Abandon the slurry and instead drill 1/4" holes in a grid across the slab and fill the void below the slab with spray foam. No idea if the foam would support the weight of the garage after the fact or if I would be able to fill the void either.

What option would you choose? What other ideas might you have? Has anyone else attempted something like this?

(More photos in the comments)

 

[DustynBeardface]

 

[DustynBeardface]

 

[DustynBeardface]

 

[Steve W.]

Maybe give a call to YOUR cousin Tony?

.

 

[bdbecker]

Following... I've got the same issue in my garage.

FWIW, I did get a quote a number of years ago to have my slab leveled using a product called 'polylevel'. The price at the time was well beyond what I could stomach - something like $7-8k. The estimator said the fact that there was a structure already on the slab wouldn't be an issue, apparently they'd seen and fixed situations like ours all the time. I'm not sure of the process they used to pull the slab back together - not sure I even asked.

Back then, they were the only game in town offering the product. Now that they have some competition, I should really get some more quotes to see if prices have come down.

 

[sjvicker]

I'm gonna be 'that guy'. If you have the skills to do the items you're suggesting above to give yourself a slab that is just kind of ok then you have the skills to remove and replace your slab. Even if you've never done flat work before I bet you could get it better than you think and if its too much for one pour you could split it into 2 short loads.

Coring holes, adding bottle jacks, hoping the slab doesn't break in two, just seems like there's a lot of costs and risk along the way that'll nickel and dime you.

 

[NUTTSGT]

I'm gonna be 'that guy'. If you have the skills to do the items you're suggesting above to give yourself a slab that is just kind of ok then you have the skills to remove and replace your slab. Even if you've never done flat work before I bet you could get it better than you think and if its too much for one pour you could split it into 2 short loads.

This is my suggestion as well. Get the old slab out and fix what is underneath it so the problem doesn't come back. If it's a year long project, it'll be worth it in the end.

However, keep in mind, you may need to do some work under the edges to completely fix the problem.

 

[DustynBeardface]

Maybe give a call to YOUR cousin Tony?

My brother, I am the cousin you call. It's either gonna go really well, or really bad, but it's gonna be a good time.

 

[DustynBeardface]

Following... I've got the same issue in my garage.

FWIW, I did get a quote a number of years ago to have my slab leveled using a product called 'polylevel'. The price at the time was well beyond what I could stomach - something like $7-8k. The estimator said the fact that there was a structure already on the slab wouldn't be an issue, apparently they'd seen and fixed situations like ours all the time. I'm not sure of the process they used to pull the slab back together - not sure I even asked.

Back then, they were the only game in town offering the product. Now that they have some competition, I should really get some more quotes to see if prices have come down.

I called up the pros first and got a 7k quote myself.

1) I don't have 7k to throw at this thing
2) Even if I did have 7k to throw at it, that 7k could go a lot further on projects that are a lot more fun
3) If I do it myself I get to justify buying tools I otherwise wouldn't need, gain experience doing something I've never done, and get to work on a project. Win/Win/Win

 

[DustynBeardface]

I'm gonna be 'that guy'. If you have the skills to do the items you're suggesting above to give yourself a slab that is just kind of ok then you have the skills to remove and replace your slab. Even if you've never done flat work before I bet you could get it better than you think and if its too much for one pour you could split it into 2 short loads.

Coring holes, adding bottle jacks, hoping the slab doesn't break in two, just seems like there's a lot of costs and risk along the way that'll nickel and dime you.

No no, see you're the guy I want to hear from. That is an interesting proposition, and I think you're right, I do have the gall to believe I could pull that off (and maybe add some height to the building while I'm at it?). Excuse me while I dive down the rabbit hole of building jacking.

 

[Fixr]

I would think that ripping it out and pouring a new slab is likely to be way less work and expense than your idea once everything has gone wrong in ways you didn't expect, and far more likely to have a satisfactory result.

So be sure to take lots of pics and videos!

 

[Fav Onefour]

I get the idea of jacking and leveling the slab. Seems like a crazy amount of work for the idea of "leveling" a broken slab.

The nickle and dime concept came across my mind as well. My concern is doing all that work for what end result. Is it the slab that is failing or the base below? Jacking and leveling doesn't fully address either of those two issues.

@DustynBeardface , You mention that the building leans to the north. Do you mean the foundation is out of level or the building is just simply leaning? Does it have footings, or is it just wall on slab?
I'd agree that it's better to save the structure and money. If the foundation/slab is out of level, it might fix multiple issues by jacking up the garage and putting in footings. That could be a DIY project and the floor can be addressed when and how you decide.

 

[racecougar]

Another vote for busting out that slab, fixing the base, and pouring new.

 

[DustynBeardface]

I get the idea of jacking and leveling the slab. Seems like a crazy amount of work for the idea of "leveling" a broken slab.

The nickle and dime concept came across my mind as well. My concern is doing all that work for what end result. Is it the slab that is failing or the base below? Jacking and leveling doesn't fully address either of those two issues.

@DustynBeardface , You mention that the building leans to the north. Do you mean the foundation is out of level or the building is just simply leaning? Does it have footings, or is it just wall on slab?
I'd agree that it's better to save the structure and money. If the foundation/slab is out of level, it might fix multiple issues by jacking up the garage and putting in footings. That could be a DIY project and the floor can be addressed when and how you decide.

I think the building lean is related to the sinking of the slab and the poor construction techniques they used to build it. There are no footings whatsoever, and based on the varying slab thickness I don't think there was much in the way of site prep done before building either.

After doing some research on jacking up the building to replace the floor, that's definitely the direction I want to go. I calculated around $900 in concrete for the 6 or so yards it will take to repour the slab. It does add in the cost of jack hammering out the old slab and disposing of it, but that's manageable. My biggest hurdle is going to be emptying the building when it comes time though.

I'm going to probably start by addressing the lean and stability issues with the building so that it's solid enough to lift. I'll keep this thread updated, but this is going to be a slow going project as time and funds allow.

 

[Fav Onefour]

Sounds like you are getting a plan together.

It will be helpful to grab a cheap laser level and verify what is out of whack. (I love those things.) No need to reinforce crooked walls. If they are straight, the process will be pretty straight forward.
I am a big fan of doing it right. I think you can see why. This wouldn't even be a discussion if the original build was done correctly. The good news here is that it looks like the process is doable.

I know it's a pain, but do you have the option of a local storage facility? I moved my large stuff a couple times into a local place so I could go gung ho on a big project. I was reluctant at first thinking it was a waste of time and money. In the end, I'm so glad I did have room to move. It made the projects more efficient. In a surprise twist, the rental unit was a motivating tool too. I busted my **** to get things done and quit using the rented space.

 

[DustynBeardface]

I actually already have the laser level, I did a pretty complete analysis of the slab when we bought the house and then laid it out in sketchup to figure out exactly how far the slab had dropped in each area. That's also how I calculated how much fill it would take to bring it back to level and also design the lighting

I'm going to keep working on the model to get an accurate idea of how far it's racking and if the corners are in square as well. Lifting the building also gives me the opportunity to address the sill plates that have rotted away from the amount of water intrusion.

Storage unit is a decent option, and you're right about it being a motivating tool. I just tend to have super heavy stuff so I hate the idea of moving it at all.

 

[Thistle2592]

I had the same problem and had a local company do the foam injection. They raised one side 10 inches. Their orginal contract had an estimated amount of foam, if it went over I would pay by the cubic foot...I amended the contract to pay for 20% more and after it was on their dime. Quote was for $3,200 without the limit it would have been over $7,000. The work was done in November of 2023.

After they were finished I stapled the broken slabs together. So far, so good.

Carbon Fiber Concrete Stitch Staple Repair Kit

NextStar 15 Carbon Fiber Concrete Stitch kit is a concrete crack control with a carbon fiber stitch system. Crack stitching and strengthening for concrete Floors, foundation walls, slabs, and swimming pools.

nextstartech.com

 

[Dig Doug]

a few things to think about

Making the slab flat / level may not fix the actual problem that is causing the cracking / movement.

need to do some discovery

What is causing the cracking / movements ?

expansive soil - clay
freezing temperature during winter expand / contract
lack of a solid foundation/ footings
moisture water / rain / drainage
no compaction to support the slab / organic materials breaking down

how far out of level is the slab, around the perimeter and then down the middle
where & How much is the building leaning
How is the structure anchored to the slab, might need to be re anchored

you need to be Very careful attempting to move the slab as the structure COULD come down on top of you
you might need some temporary bracing to secure the walls and the roof system.


I could live with an out of level slab, a lot of garages are slopped to flow water out the garage door.

looking at this from my recliner

Im thinking -
saw cut the concrete and remove a 15, 18 or 24 inch strip to eliminate the cracks
epoxy dowel in rebar to marry everything back together

keep in mind that you have independent 4 corners of the slab that are not connected to each other and once you start to push pull tweak
the roof can come down on top of you, like a deck of cards.