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Re: large cracks in slab

To: Keith Turk <kturk@ala.net>
Subject: Re: large cracks in slab
From: Scott Hall <sch8489@garnet.acns.fsu.edu>
Date: Fri, 6 Dec 2002 00:30:30 -0500 (EST)
On Thu, 5 Dec 2002, Keith Turk wrote:

> Scott... Almost every single slab I've ever poured or seen has crack's..
> it's a normal result of shrinkage in the first 28 days of curing.... if it's
> 56 days old it's most likely done shrinking....   ( your mileage may vary )

forgot to mention that...it's probably close to ten years old.  my bad.

> Now the normal size of the crack is porportional to the quality of the
> concrete itself.... house slab's by BOCO, IBCO or SBCCI  allow for the use
> of 3000 psi concrete.... or a 4.5-5 bag mix.... ( meaning there is
> 450-500lbs of cement per cubic yard )  bottom line if the water content for
> that cubic yard was stretched to make it easier to pull ( float ) on the

I was thinking that maybe since the slab is so big and probably was hard
to float (at least 40 x 40 at it's smallest part) and there aren't any
joints that is *should* crack.  but these are mighty big cracks...

> set on a PURE flat situation... if the ground is sloping more then a foot or
> so... well I'd be much more concerned....

in front of the garage it slopes maybe four feet down real quick.  and
there's a crack there, too.  but not as big as those actually in the
house.  either side of the house has a shallower slope.  nearly flat in
back.

> flooring and I'd make a point to the builder that I was concerned and going
> to have the actual crack measured along it's distance for a couple of years
> and he would sign a letter saying he understood my concern and would extend
> the warranty appropriately...

probably not an option here...

> Okay now for the Caulking.... I'd be fine with that.... but I'd also be okay
> with a simple mortar mix type patch floated into the crack with say a screw
> driver type device.... my thoughts being your more likely to get quality
> penetration with cementatious products then you are with Caulk type
> patches.... You do have to do something because water in some form or
> fashion is going to migrate...

I do want to keep out the water.  but what about keeping the slab
together?  one of the cracks runs under some tile in the kitchen, right
under a grout line.  you can see where the grout line has started to
crack.  that's making me worry that thte cracking wasn't just from the
shrinkage when it cured.  unless they put the tile down that quick, which
I don't know.  the cracks are level, but otherwise it looks a lot like the
slab was being pulled apart but a giant hand.  big, jagged (and wide(r
than I'd like to see)) cracks.  any idea how wide is too wide?  1/4 inch?
1/8?

> I'm a builder but don't do a lot of concrete work under houses.... I own a
> concrete manufacturing business that makes veneer stone products... So what
> I'm saying is mostly off the top of my pee brain... and keep in mind that
> CRS stuff ...

no sweat.  thanks for the reply.

scott 

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