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Old 02-19-2009, 01:14 PM   #1
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concrete cap


I have a detached garage that is 20x20. It is a concrete floor and probably 40+ years old. I bought the house 7 years ago and the floor was cracked and had shifted. To my untrained eye it has not moved since I have owned it. It is at minimum 6" thick on one side and the other is at least 10" thick.


my budget doesn't allow me to tear out the floor and replace it.

So, what I'd like to know is, can successfully I put a 2" or 3" cap on this floor?

What are the pros and cons?

Thanks
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Old 02-19-2009, 02:05 PM   #2
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The problem of pouring over the old surface with a new one is that you still haven't fixed the problem that caused the old one to crack. That said, perhaps the soil under the old slab was not compacted or it was not prepared properly or had poor fill. Maybe it'll move again and then again, maybe it won't.

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Old 02-19-2009, 02:22 PM   #3
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Yes you can put concrete over the old. First it must be clean and dry. Then add a bonding agent to allow the old to stick to the new. As long as you are sure it is no longer moving as suggested by the last post.
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Old 02-19-2009, 02:23 PM   #4
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Well, what ever the problem is/was wouldn't it continue to show itself... i.e. wider cracks, additional cracking/shifting each year?
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Old 02-19-2009, 02:24 PM   #5
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Quote:
Originally Posted by Bob Mariani View Post
Yes you can put concrete over the old. First it must be clean and dry. Then add a bonding agent to allow the old to stick to the new. As long as you are sure it is no longer moving as suggested by the last post.


What should the minimum thickness be?
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Old 02-19-2009, 02:52 PM   #6
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Un-bonded minimum of 3". Some bonding agents let you go as thin as 3/4". Any joint cuts should go at least 1" into the base slab.
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Old 02-19-2009, 02:57 PM   #7
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What should I fill the cracks with? Most of them are at least 1" to 2" wide
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Old 02-19-2009, 03:22 PM   #8
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just fill with the new top coat
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Old 02-19-2009, 03:32 PM   #9
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Thanks for all the help guys... one more question.

One of my side walls and a center support beam sit on the old floor. What would be the best way to deal with these?
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Old 02-19-2009, 04:25 PM   #10
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If it truely needs to be fixed, fix it correctly or you will be sorry. Pouring over it is not a good idea. Most all concrete is going to crack. Cracks are ok, ugly, but ok. If the concrete has broken and seperated much at all, you have a geological problem that pouring over it is not going to fix. If it isn't a geo. problem, then 2" of concrete may not be a good idea. It will look ok over time but it will be difficult to do anything to the existing concrete that will prepare the surfaces avoiding a cold joint. What will happen after time is the 2" will start craking and coming up on its own. Most concrete books, manuals, and the like highly discourages against anything less than 4". If you pour 4", you need to think about all your doors getting into the garage. They will all need to be reset, which will mean either a sawed off custom door or major work in raising headers regardless of it being framed or block.

My advice, if it ain't falling over, don't fix it. Chances are, whatever caused this happened within a couple years of the concrete being poured and is fine now. If you absolutely must, hammer it up, take it out, and repour it.

Post us a picture and we can tell you if this is something to worry about or not.
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Old 02-19-2009, 09:45 PM   #11
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I wouldn't fix it, and I'm not. Save up to tear out and do it right. I've got the same issue and it drives me nuts. However, I do know that pouring a "cap" over it will never work. First of all, you never really know if the soil movement is still active, unless you get super scientific, so there's a good chance you'll see cracks again soon. You'll be paying to adjust doors, as mentioned, and all other framing likely when adding concrete to the existing floor. All in all, it's half-assed and wouldn't be worth it.

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