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Old 06-18-2008, 02:10 PM   #1
mikeyr
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Default replacing garage floor

The house I am moving into has a older garage with a badly cracked floor, cracks are in several places with the worst running about 12ft. diagonally and 2" to 3" apart in one place, the structure of the garage seems fine as long as the termites don't sneeze.

The thing is what the city calls legal non-conforming as it was built in 1951. My first thought was tear it down and rebuild but the city wants me to move it 8feet from the property line if I do that, it currently is 2feet from the line. I don't want to lose 6feet of my yard and have 8feet wasted space on the side so I am leaving it up and fixing it one wall at a time.

Back to the slab its badly cracked but there is no seam at the footer, it looks like the footer and slab was poured all in one pour instead of a footer and then slab, how do I get the slab out ?

I am guessing a concrete saw and get as close to the wall as I can ? luckily I have confirmed there is no rebar in the slab. OR would it better just to float a new slab on top of the old one ? I really hope not because my lift needs 4.5" of good concrete under it.
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Old 06-18-2008, 02:37 PM   #2
6t7gto
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Default Re: replacing garage floor

You have a monolithic floor.
My dad has one and it cracked. We laid a 2x4 along the wall and cut the floor with a concrete saw.
removed the cracked floor and poured a new one.
drill some holes in the remaining concrete and install some re-bar. (under pinning the new floor.)

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Old 06-18-2008, 04:32 PM   #3
Kevin54
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Default Re: replacing garage floor

Quote:
I am guessing a concrete saw and get as close to the wall as I can ? luckily I have confirmed there is no rebar in the slab. OR would it better just to float a new slab on top of the old one ? I really hope not because my lift needs 4.5" of good concrete under it.
Quote:
You have a monolithic floor.
I hate to say, but you had better talk to a structural engineer before you cut anything. A monolithic pour, where they pout the outer edges thicker, may not be strong enough to support the building once the floor is cut away. The structure would need to have a different style of foundation to support it. By that I mean, it would need a footer, rebar, and walls up to the sill plate. With a monolithic floor, the floor helps support the structure by tying the floor, and whatever small foundation there is together. I would imagine that over time, some of the foundation has settled, therefore causing the cracks to go through the floor. I would remove a wall at a time, support the structure with what you have, then redo the foundation to where it would be able to support what you have. You may be grandfathered in on your structure if you leave just one wall. A lot of the remodeling shows in the past, and even This Old House, got around a lot of things by tearing down everything but one wall and doing a total rebuild. Worth looking into before you end up with real structural damage.
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Old 06-18-2008, 04:49 PM   #4
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Default Re: replacing garage floor

I have a similar issue. I have been lurking here for a couple years picking up pointers on this and that, and trying to get caught up on other house projects before I dig into my garage build. My carport slab was poured as part of a larger sidewalk project, I think, 15-20 years ago and for whatever reason they never cut any control joints or made much/any effort to finish the surface. So, the surface kinda sucks. I have watched the cracks closely since we moved into this house three years ago, and while a couple are 1/4" or so wide, the floor's not moving (not to say it won't, but I think I'll be OK). So I am planning on building the garage on the existing floor, leaving the footer across the door frames, and filling in the floor up to that level with a self-leveling and/or fiber-reinforced topping slab. Thick enough to have some strength, flat enough to be a nice surface to seal/ coat/ roll a creeper on, and still low enough to drive anything onto without concern. Since I don't have the height for or plan on adjusting the roof to accomodate a lift (that's still years out in the barn I want to build), I think I'll be OK. I hope.

Or, I might convert the carport/garage, get it dried in and "done" and then cut the floor out and repour. I am seriously on the fence, and I imagine that'll be the case until I get down to fish or cut bait time. I really REALLY don't want to go through a slab demo, though.
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Old 06-18-2008, 07:07 PM   #5
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Default Re: replacing garage floor

I have to have a engineer look at the place anyway for the extension I am doing so I will bring that up with him. Cosmetically, the cracked floor really does not bother me in any way since I will cover it with Racedeck tiles but because my 4-post lift is going on that floor, the cracks concern me for strength.

I can most likely do one wall at a time and rebuild but that will really mess up my schedule, I would much prefer to get the floor fixed so I can put the lift on and after I am moved in worry about the details of rebuilding. Yes, I know bad way to do it but I am paying 2 mortgages until I move in.
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Old 06-19-2008, 03:19 AM   #6
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Default Re: replacing garage floor

Is the garage attached to the house? If not, I bet you could have the wooden structure jacked up and jackhammer the floor out, then repour. You may even be able to add a bit of height and /or drop the floor down a bit.

I imagine this would be pretty expensive, of course
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Old 06-19-2008, 05:55 AM   #7
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Default Re: replacing garage floor

If your not concerned about the appearance, then figure out where the posts from the lift will be and mark them on the floor. Draw a 16x16 square (or larger) centered on the mark. Saw cut these areas out. Dig down until you find good solid earth with sufficient bearing capacity (hopefully your garage is a slab on grade vs a structural slab with grade beams). When you dig, make the earthern hole larger then the cut-out by about 4 inches all around - this will give the slab a ledge on the new pier for support. Place 2 #4 rebars about 2 inches off the bottom running front/back about 2 inches from the sides and another similar matt of bars running left/right on top of this - wire them together at the intersections. Pour new piers in these areas (3500 psi mix or better), vibrate to remove air pockets, and trowel the surface smooth with the adjacent surfaces. Perform cosmetic repairs to the remaining surface or cover with the Race Deck as you suggested. Position/mount your lift on the new piers - do not use the lift until the concrete strength has come up adequately. Typically, in 7 days you will get 70 to 80% of a the concrete strength with full strength in 28 days.

Same technique is done all the time in houses to add/relocate column loads in basements to accomodate structural issues or rennovations requiring re-posting of loads. I have also done it in new houses many times when the concrete contractor screwed up and missed a pier for a column.
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Old 06-19-2008, 09:33 AM   #8
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Default Re: replacing garage floor

great idea larry4406.
You could also use some extra concrete to fill in the cracks and then cover with the racedeck.

I believe that would be the most economical way to add the lift to your garage. And you could probably do it all yourself for less than $500.

If you tear down, you will have to comply with current codes (i had to do the same thing) but the setback's were'nt as large as yours (and there was no help for my old garage)
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Old 06-20-2008, 12:58 AM   #9
mikeyr
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Default Re: replacing garage floor

I am considering lifting the entire garage and doing proper footings and slab.

But if the city gives me ANY grief, then 16x16 or 24x24 cuts and new concrete for the lift as Larry said, I like that idea
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Old 06-20-2008, 10:50 AM   #10
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Default Re: replacing garage floor

Not sure what the bearing strength of the soils in your neck of the woods is, but in here in northern VA I have dealt with soils as low as 1500 pounds per square foot and as high as 2500 psf. So to put that in perspective, a single 12x12 inch pier can support a minimum of 1500 pounds. At this amount, that would be 6000 pounds of combined lift and vehicle. So the moral of the story is work the pier size along with the bearing capacity to support the intended load while making sure the concrete can transfer the load.
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Old 06-24-2008, 02:22 PM   #11
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Default Re: replacing garage floor

Well said Larry! you must be a fellow Engineer. Mikeyr I wold suggest doing what Larry said as this is your most cost effective solution to your problem. Just make sure you make your piers the correct size according to a soils report!
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