Replacing cracked and settled garage floor?

[ddlaz]

My mom's detached two-car garage floor is severely damaged. Some cracks are 2 inches wide and there are probably 10 different floor elevations from the cracked up floor.

I haven't looked at it in a couple of years but I believe the framing is still in good condition.
What I'd like to do is replace the floor but I had some logistical questions.

1. Thought process: remove interior concrete, jack up structure(with ledgers and bracing), remove footings, dig out perimeter to pour 12x12" footing, set garage back down, pour interior concrete at 4". Is this how the experienced DIY'ers would do this? If not, enlighten me.

2. Since the footing will be under the garage, how do you put in and compact the class 5 under the footing? Is it necessary with a footing?

3. If the structure isn't sagging at any particular corner and the footings aren't cracked through, would it be acceptable to just cut, remove, and replace the interior concrete only? I don't want to do a hack-job, but since it's just a garage...why not?

Thanks in advance as usual!

 

[ford33]

First ask yourself is the structure worth the effort. What you propose is a huge job for a homeowner to consider.

It likely is easier, cheaper and offer time savings to tear it down and start over. Usually a lifted open three sided structure is difficult to pick up and put down on a new foundation and have everything line up again. Keeping the structure together while doing the foundation work is also another challenge.

There is a thread on here from last year about someone who did it and he was a skilled tradesman with a helper and a tractor. It's an interesting story presenting the troubles and triumphs of attempting this work.

 

[ddlaz]

I've built a couple of large stick built garages/man caves on slabs so I think I can handle the project. When considering if the structure is worth it or not, I am taking into account that these costs:the wood to lift the house with some bottle jacks is going to be about $500 +/- $100, the concrete would be about 11 yards but adding 20% to account for discrepancies is about $500, class 5 at $200. We'll just say $1500 in materials for lift and replace. That cost versus new wood, sheathing, siding, shingles, garage door, etc... would be about $5500 alone. BUT you'd still need new concrete and likely class 5 anyways so to compare the two, you'd have to exclude concrete from both options.
If you're also considering costs of manpower and/or machinery, I have a skidsteer and dump trailer at my disposal along with family and friends. They just aren't handy with a hammer...
Am I overlooking some other costs?

 

[ard]

What kind of floor and foundation does it have now???

if there is a footer and stem wall, with a separate slab- these can be independent.

If it is just a monolithic slab, with maybe thickened edges, less so....

Where are you? or mom? frost depth?

 

[ddlaz]

mono with thickened edges. MN frost depths were 54" IIRC.

 

[Copymutt]

Did this two summers ago to a mono pour that was laid over unprepared expansive clay and aprons around the house sloped to the house. This guy did nothing right. 4" heave down the center and 1" to 3" cracks.
I will say his absence of rebar made it a lot easier to remove. Everything went in and out through a window via a bobcat. I got multiple bids, most were flakes just by talking to them. I got it done by a contractor that bids mostly municipalities jobs. His crew needed a four day filler till next project.
15 x 30 4" slab, removed a foot of the clay, replaced with gravel, compacted, vapor barrier, pump truck thru the window, perfect troweling and finishing. Just cut inside the framing and left the thick part of the pour and the stem/ footer part. All for $6000.00. Other bids were $15k and they'd fit it in between other ongoing jobs,NOT. I could read between the lines where this was going.
This was one time I hired it out and very glad I did. Be sure to fence off anything that rolling equipment can damage, including well, septic, power drops, freeze proofs, etc.
Jim.

 

[bdbecker]

Jim- did you pin the new pour to the existing perimeter concrete? I'm thinking this is the route I'm going to take with my garage someday.

 

[Leaflessshadetree]

Aroud here concrete is close to $100/yd.
If the footers and foundation are good I'd just break out the center, redo the compaction (add rock if necessary and repour).
If redoing the foundation (or doing a mono slab) it could be easier to prepare the new next to the old and move the garage to it.

 

[Copymutt]

Jim- did you pin the new pour to the existing perimeter concrete? I'm thinking this is the route I'm going to take with my garage someday.

Yes, drilled into the perimeter and set rebar to tie in to new slab pour. When I've connected other pours to existing foundations I also epoxied the rebar in place. Didn't do it here as I see now possibility of any movement.
Jim

 

[Lunker]

I tore out a garage floor last year in a house I was flipping. Cost me $3500 the final product turned out ok. they saw cut the floor around framing tore out the floor, pinned it into the perimeter with rebar and repoured it. At the end of the day rehabbing the Garage saved me $5500 vs building new. I spent another $6000 on roof, hardie Siding and aluminum, and New garage doors

 

[matt_i]

If it isn't sagging or out of line, I really like the idea of having it professionally saw cut close to the walls, edge-drill and pin with rebar.

You have to fix the issues with why it broke apart though. It could be voids in the subgrade...or poor concreting (lots of water resulting in low strength). I would go back with steel reinforcement.

 

[D45]

The front 4 feet on my garage was in bad shape and the driveway was cracked and sinking in spots

The house was built in the 70s and most of the sand under the washed away...…..I guess they just to only use sand? The concrete place told me that gravel is only used now and is heavier, and wont wash away and will support it better

The also saw cut the curb, poured a new apron, re-coated the porch and poured a new small walk way from the front porch to the driveway

It was like $6000 for everything

 

[lakeroadster]

3. If the structure isn't sagging at any particular corner and the footings aren't cracked through, would it be acceptable to just cut, remove, and replace the interior concrete only? I don't want to do a hack-job, but since it's just a garage...why not?

Thanks in advance as usual!

Welcome new guy...

First question is.... Will you need a permit to do this renovation?

The idea of cutting the slab adjacent to the inside edge of the sill plate really changes the entire structural integrity of a thickened edge monopour foundation. I doubt you can get approval to do this as a permitted project, and doubt you can find an engineer that will approve it.

You may end up with a nice new floor... and then start to have structural issues.

Proceed with caution.

Is the lot big enough that the building could be moved to another location? Then you'd be able to have unobstructed access to remove the existing slab and start new. Then move the building back onto the new slab after 28 days.