Destroyed Concrete Floor

[Alexztt]

My 2 car floor seems to have lifted in the middle and cracked in multiple pieces off from there. It was like this when I bought the place. I plan on putting two 2 post auto lifts in this garage, so I need several inches of good concrete to bolt to for it to be safe. I am pretty sure I have to R+R the entire floor. My question is what to I do so this does not happen again. (Will post pics shortly)

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Basically this is what has happened I all different directions. Right to the footers.

 

[red]

One of the more experience concrete guys will chime in, but it could be one of two things.

First the sub-soil settled or wasn't compacted properly or worst yet construction debris could have been buried there.

Secondly could be tenting where the middle pushed up cause had no where to expand to - not very likely usually only see that with tile without expansion joints left in it.

Are there any water issues? Could water be washing away your base or freezing causing heaving the concrete.

 

[rsanter]

What about roots under the garage

Bob

 

[Zeke]

I'd remove the slab and look at the soil/base. You may want to take a few inches of that out too and replace with compacted base material. The when laying your rebar, dowel some of it into the existing footer.

 

[Alexztt]

Now that you guys say it. The nieghbors that have been here forever have told me there was a huge rock that was blasted out before they put up the garage. You think maybe they didnt get rid of enough of it?

 

[Alexztt]

There are no expansion joints in the floor if that makes a difference. Nor does there seem to be any signs of water damage. No water comes up thru the floor.

 

[zporta]

I would r&r the slab. It appears that the subgrade settled and the slab reinforcement wasn't tied into the foundation.

In all the garages I pour I use #4 rebar 24" both ways o.c. And drilled into the foundation around the entire perimeter

 

[ConCretin]

Personally I wouldn't bolt a lift to a slab I knew nothing about especially one that is as distressed as yours. The displacement of the existing concrete resulted from an inadequate base that settled, heaved or both. To correct this condition, you'll need to remove the slab anyway.

Your base should consist of 6-12" of well compacted, granular material. Make sure there is no organic material and check for proper drainage. Don't forget to protect the base material and native soils beneath it from freezing.

There's plenty of good advice on here about how to properly construct the new slab. I differ a little on pinning the slab to the foundation. You want the slab supported by the sub grade plus the dowels can restrain contraction and cause cracks.

It will be a lot of work to remove the slab and correct the sub-grade but if you want a lift, it's probably necessary.

 

[Alexztt]

So there is most likely a problem under the slab. Fantastic. I will not bolt a lift to this slab which is why I am trying to figure out what my issues are. I want to get the floor taken care of first before I do anything else. Next question is does anyone know a good contractor that I can trust in my area.

 

[rsanter]

Yes I agree there is a bro elm under that slab, but don't get too dismayed as it's all fixable
I would remove the slab and do an eval of the ground under there.
Think about digging out some of the dirt and adding some base that gets compacted
Then add your slab back in with the required footing for the lift

Bob

 

[Alexztt]

I understand settled but was does heaved mean? I am a big DIY guy but only if it can be done properly. Do the guys that have done this before or the professionals on here think I can do this myself?

 

[dwm]

Heave is generally the result of expansion/contraction from freeze/thaw cycles (water changing to ice and back). That's why folks are recommending you remove some soil and fill/compact a new base of something that drains reasonably well. Where I am, there is a lot of dense clay which holds moisture and causes frost heave in the winter. Tears deck ledgers off walls of the DIY decks that don't have proper depth footers, breaks improperly installed sewage lines at the foundation, wrecks our roads, moves our driveway slabs, etc.

 

[Justanoldguy]

If you not wanting to remove the floor but still want a lift.
I suggets cutting out 2 squares where you are going to bolt the lift to.
About 2ft x 2ft by 2ft deep and pour new concrete in there.
If you can live with the floor then at least the lift is safe.

 

[Dan in Pasadena]

Now that you guys say it. The nieghbors that have been here forever have told me there was a huge rock that was blasted out before they put up the garage. You think maybe they didnt get rid of enough of it?

The problem ISNT that they didn't get rid of enough of it. The problem is likely that they removed it to below grade (or completely) and filled it up without properly compacting the soil. That's how you get settlement and the resulting cracking.

Remove the lab, remove the un compacted fill, backfill and compact properly (or use slurry) then replace the slab.

 

[Alexztt]

I dont have a problem removing the slab. I am more worried about if I will be able to prep the base and pour the slab properly. With only what I know from reading and other research that I will do.

 

[StillSmokey]

I wouldn't recommend placing and finishing the slab yourself. However it may be worthwhile to look at renting a bobcat/dump trailer and doing the demo and prep yourself.

Personally if I was doing a lift, I'd be putting pilings where my posts are going.

 

[ADSR]

I understand settled but was does heaved mean? I am a big DIY guy but only if it can be done properly. Do the guys that have done this before or the professionals on here think I can do this myself?

This is easy DIY stuff. Rent a 65lb jackhammer and give it ****. Place all the broken concrete off to the side. Dig out the dirt or clay down 12 - 20". Throw all the broken concrete back in the hole. Fill it up with roadbase and compact in 4" lifts. Grade for 6" and drill in 5/8's rebar every 4'

 

[Alexztt]

So putting the concrete back in the hole is acceptable? What is roadbase? Do I need equipment to compact? This seems like the most important part.

 

[ADSR]

So putting the concrete back in the hole is acceptable? What is roadbase? Do I need equipment to compact? This seems like the most important part.

The concrete is clean hard fill. I always try to use it on the jobsite and save the customer money. Roadbase is 3/4 - with fines. It's what used underneath roads before concrete or asphalt. Most guys use fill sand, but it's not as hard.

You'll need to rent a plate compactor and run it over the base in 4" lifts. The more times you go over it, the better.

 

[Morrison]

I would pay someone to do this. I like doing everything I can as well but someone who does concrete for a living will probably give you a better floor.

Do the demo with to save some money if you want.

 

[ADSR]

I'm wondering if the foundation has shifted. You can't really tell from the picture, but this is what i can see.

 

[danski0224]

I'm wondering if the foundation has shifted. You can't really tell from the picture, but this is what i can see.

The top of a foundation/footing is typically not level in residential construction.

The mudsill is shimmed level and the gaps are supposed to be filled in.

If the gap you show in the picture between the mudsill and the concrete "suddenly appeared", there would be no doubt about cracking in the foundation.

You have a perimeter footing and a floating slab. Typically, the foundation/footing should extend below the frost line, even if it is a trench footing.

Local codes/practices would dictate whether or not there is rebar tying the slab to the footing. If it was a monolithic pour (footings and floor at the same time), there would be rebar in there.

Something isn't right under the slab.

You will have to bust it out to fix it. Excavate to undisturbed soil and start over. Put tubing in the concrete for radiant heat this time.

An alternative, if the crack itself isn't objectionable, is mudjacking the slab.

 

[volleyball]

Since you are a DIY guy, what I would suggest is you have a few months before you can do this. First decide what all you want. Do you want it pitched to the outside? Do you want a drain? Do you want in slab heating? Where is the lift going?
You then can dig out the old slab. Determine what is there. I doubt the huge rock is the problem. It probably isn't going anywhere. More likely the soil heaved or shrunk while the ledge did not.
I am betting no base so dig down for enough room to lay base. You can use some of the small pieces of old concrete but toss all the chunks. Fill in with 3/4" and compact. you'll want some heavy mil plastic on top of that and 2" or more of foam. the thickness of your slab should bring you to grade.
I would have a pro do the slab. Someone with a power trowel to give it that finished look and make the surface harder. I looked into getting help and renting the equipment and the numbers were not good.
You also have to look at the surrounding area. Is the garage level, higher or lower than it? Any drainage going past the garage? Any idea of when the existing slab was poured? A recent floor in an old garage could mean nobody has done it right and it still fails.
For the lift. you may want to run the power in conduit in the slab. I would also see what the mfg wants as far as footing. Since a lift has more stresses than a floor post would, a rebar cage might be valuable. Cheap and easy to dig and make when you are in just dirt. Expensive when you have a fresh floor.

 

[Alexztt]

Foam under the concrete? What is that for I have never heard of that? LORDDIESEL the footing does not have a crack sorry for the crappy picture. I am in no way a pro but to me it does not seem like the fotting has shifted at all. None of the damage is new but I have only owned the house for a year and a half. On that note the garage itself is less than 10 years old. Is there something I can look for as far as water damage?

 

[Fixnfly]

So what would the cost be to pay someone to do this work?
Just a ballpark figure, I know every job is different and and it depends where you live.

 

[ADSR]

The top of a foundation/footing is typically not level in residential construction.

What the hell are you talking about? I've only put in 100 - 150 foundations as a carpenter. If you can't get the top of the foundation level, you better find another career.

 

[ADSR]

So what would the cost be to pay someone to do this work?
Just a ballpark figure, I know every job is different and and it depends where you live.

OP didn't post size of garage, or i missed it. A big two car garage with a 4" thick slab would take a 6 - 8 hours for 2 guys to hammer out and remove. Another 8 hours for 2 guys to dig the garage out. Then prob 8 more to compact/fill/grade getting it ready for the pour.

4 days to play it safe.

 

[ADSR]

Foam under the concrete? What is that for I have never heard of that? LORDDIESEL the footing does not have a crack sorry for the crappy picture. I am in no way a pro but to me it does not seem like the fotting has shifted at all. None of the damage is new but I have only owned the house for a year and a half. On that note the garage itself is less than 10 years old. Is there something I can look for as far as water damage?

There should be plate gasket under the wall by code. The only thing i would look at is the footing under the slab after you hammer it out.

 

[Alexztt]

What on the footing should I look for? Also how far down do I have to dig if I want to pour in 6 inches of concrete? I have an average 2 car garage. I have never actually measured it before. Thanks for all the help.

 

[volleyball]

Foam under the slab insulates it. Especially good if you heat the space.
Until you know what is under the slab, you don't know how far you have to dig. slab depth + foam + base material. could be 14" with a 6" slab which I think is over kill.

 

[ADSR]

Foam under the slab insulates it. Especially good if you heat the space.
Until you know what is under the slab, you don't know how far you have to dig. slab depth + foam + base material. could be 14" with a 6" slab which I think is over kill.

This^

You won't know how far to go until you get in there. 4" slab will be fine without a lift. 6" if you want a lift. If it was mine, i would put at least 2" of white foam in it. 4 x 8 x 2 white foam is under 20 bucks a sheet and has a 7.5 R value. Well worth the money IMO.

 

[anthony666]

This^

You won't know how far to go until you get in there. 4" slab will be fine without a lift. 6" if you want a lift. If it was mine, i would put at least 2" of white foam in it. 4 x 8 x 2 white foam is under 20 bucks a sheet and has a 7.5 R value. Well worth the money IMO.

x2 .. even if you don't heat the floor, or don't heat the shop at all

 

[Alexztt]

That is a great idea. It must cut down on how cold the concrete gets dramatically. How thick should the base be? I know we were talking about compacting every 4 inches that leads me to believe it has to be pretty thick. Does it depend on what I have underneath and the damage incurred or is there an average thickness it should be?

 

[volleyball]

We don't know. We said that. 4" may be enough. I like to compact the soil, then every 2" of base above that.
If you can live with pulling up a section then you can get a better idea. But you cannot do the job correctly now. I say revisit when you are prepared to do this in the spring. We should still be here.

 

[farmer_ryan]

i wouldn't use a foam under the slab unless it was rated for sub grade use. once your foam absorbs a little water it is useless as an insulating material.

as for the concrete, i had a guy tell me one time just to pour it 12 inches thick and not worry about it.

 

[ADSR]

i wouldn't use a foam under the slab unless it was rated for sub grade use. once your foam absorbs a little water it is useless as an insulating material.

I don't think anyone here would be dumb enough to use open cell foam under concrete.

 

[farmer_ryan]

I don't think anyone here would be dumb enough to use open cell foam under concrete.

You might be suprised.....

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[Justanoldguy]

What the hell are you talking about? I've only put in 100 - 150 foundations as a carpenter. If you can't get the top of the foundation level, you better find another career.

Agree totally

 

[Justanoldguy]

You might be suprised.....

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Well I figure the advise about the foam was said in a sensible manner.
Not here to talk about the odd idiot out there that does everything outside the norm.

 

[farmer_ryan]

I would also consider putting a vertical piece of insulation along the edge. Like along the block or between the posts. I did this in my shop and I really think it helps keep the cold from working under the edge of the slab.

Is 6 inches think enough concrete for under the lift?

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