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-   -   Cracks appearing in garage slab (http://www.diychatroom.com/f19/cracks-appearing-garage-slab-12080/)

tripower 10-03-2007 07:40 PM

Cracks appearing in garage slab
 
I have a new (5 months old) slab; approximately 25' X 30', 4" thick, 3500psi, wire mesh and fiber reinforced.

The slab was allowed to cure over a month before anything heavy was put on the floor.

About a 2 months ago a hairline crack developed near the middle of the floor. And now I see a new hairline crack appearing length-wise.

Needless to say I am not to happy about this.

Should this be something that I should be concerned about with the integrity of the floor or is it more of a cosmetic issue?

97catintenn 10-03-2007 07:47 PM

It stinks, but thats what concrete does. It cracks. But thats not as bad as having a low spot in the concrete floor and when it rains hard, the rain comes in under the garage door and puddles inside the garage.

That really stinks!

I believe yours to be purely cosmetic.

tripower 10-03-2007 07:55 PM

Quote:

Originally Posted by 97catintenn (Post 66189)
It stinks, but thats what concrete does. It cracks. But thats not as bad as having a low spot in the concrete floor and when it rains hard, the rain comes in under the garage door and puddles inside the garage.

That really stinks!

I believe yours to be purely cosmetic.

I wanted to put a four post lift in my garage and now these cracks have me worrying about the integrity of the floor. Should this be something I need to worry about?

concretemasonry 10-03-2007 08:22 PM

You should have had control joints sawed in th slab to control where the cracks will occur and eliminate the appearance of random cracks. Nothing can be done about that now.

If you want to put in a lift now and not increase the cracks, saw cut the locations (diamond shape at each post) of the post locations and put in a separate Sonotube footing. That way you will support the lift independently of the slab and not worry about cracks and settlement that could screw up your drainage.

tripower 10-03-2007 08:30 PM

Quote:

Originally Posted by concretemasonry (Post 66196)
You should have had control joints sawed in th slab to control where the cracks will occur and eliminate the appearance of random cracks. Nothing can be done about that now.

If you want to put in a lift now and not increase the cracks, saw cut the locations (diamond shape at each post) of the post locations and put in a separate Sonotube footing. That way you will support the lift independently of the slab and not worry about cracks and settlement that could screw up your drainage.


Thanks for the advice. It's a great idea. Do you know of any web links where someone has done something similar?

kemerick 10-03-2007 08:33 PM

I don't know of any web links but I just wanted to second the great idea...

97catintenn 10-03-2007 09:47 PM

I've never dug a diamond shaped footer, but a footer is needed. A four post lift requires a concrete footer a certain width to bolt to right? I mean the metal flange on the bottom of the metal post is going to be something like a 10"X10" or a 12"X12" flange. So your footer needs to go out past that about 4"s. Making the footer either 14X14 or 16X16. Dig down till you hit solid dirt and at least 8"s deep.

You asked for pictures, but if I posted pictures, it would be of cut concrete with some over cut marks and new concrete poured. You will be able to tell by looking at that you did this as an add on.

Unless you do some cosmetic work.

If you do not do this, then you may attaching your lift to a section of concrete that is not the full 3.5"s that concrete pads normally are. Keep in mind that they form them with 2X4's and those measure out to 3.5"s. And after they spread the grade and pour the concrete and may end up being less.

tripower 10-03-2007 10:04 PM

Quote:

Originally Posted by 97catintenn (Post 66209)
I've never dug a diamond shaped footer, but a footer is needed. A four post lift requires a concrete footer a certain width to bolt to right? I mean the metal flange on the bottom of the metal post is going to be something like a 10"X10" or a 12"X12" flange. So your footer needs to go out past that about 4"s. Making the footer either 14X14 or 16X16. Dig down till you hit solid dirt and at least 8"s deep.

You asked for pictures, but if I posted pictures, it would be of cut concrete with some over cut marks and new concrete poured. You will be able to tell by looking at that you did this as an add on.

Unless you do some cosmetic work.

If you do not do this, then you may attaching your lift to a section of concrete that is not the full 3.5"s that concrete pads normally are. Keep in mind that they form them with 2X4's and those measure out to 3.5"s. And after they spread the grade and pour the concrete and may end up being less.


Actually, four post lifts usually don't bolt in. But all 2 post lifts do, so I don't think that is an issue but never the less cutting in separate footings seems like a great idea.

97catintenn 10-04-2007 07:29 AM

Thanks for the info, I was thinking that they all were bolted to the floor.

tripower 10-15-2007 08:33 PM

Quote:

Originally Posted by concretemasonry (Post 66196)
You should have had control joints sawed in th slab to control where the cracks will occur and eliminate the appearance of random cracks. Nothing can be done about that now.

If you want to put in a lift now and not increase the cracks, saw cut the locations (diamond shape at each post) of the post locations and put in a separate Sonotube footing. That way you will support the lift independently of the slab and not worry about cracks and settlement that could screw up your drainage.

What should I put on the cracks to reduce their appearance and prevent water from seeping in?

kemerick 10-15-2007 09:06 PM

I have used the Quikrete Concrete Crack Seal:

http://www.quickrete.com/ProductLine...eCrackSeal.asp

...but it has dried out and needs to be redone already after a year. The cracks have grown a bit and it has been exposed to the mild elements here in Southern California. It may work better for you however being in a garage.

If the cracks have stopped growing I would try mortar. Its cheap enough to give it a shot...

murray59 10-16-2007 12:00 AM

Around here the code for garage slabs has gone to 5" thick and rebar reinforcement. Then they saw in lines to control where the cement cracks. As for footings for the lift, I was thinking a 4 post lift with car wouldn't have much more weight than a 4 wheeled car so why bother with footings for it unless it's a 2 post lift.

Ron6519 10-16-2007 04:01 PM

These lifts can be in the 1500- 1700 lb range. You store one car on top and park another underneath. That's alot of weight on a 4" slab.. Once you pour the footings, the lift and the car it carries don't factor into the load on the floor.
Ron


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