# Cement Compound.



## Foundatio (Mar 2, 2010)

I recently had a foundation specilist come take a look at my slab due to some issue we were experiencing, and he says our issue isn't our foundation. He pointed out where a side walk running along the slab is coming apart from the main slab, allowing water to go directly under it and push it up. He suggested using a compound to seal the two together. What should I use?


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## TxBuilder (Mar 3, 2010)

Welcome! There are some Concrete guys around here I'm sure would be happy to help.


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## Nestor_Kelebay (Mar 3, 2010)

What's commonly used to seal cracks in concrete foundations where I live is called "hydraulic cement".  This is a cement mixture that expands as it cures, and that causes it to form a tight seal in the crack.

PS:
I'm going to start out by saying that I'm certainly no concrete or foundation specialist, and there are people in here that know much more than me about both.  However, I just don't see why water getting into a crack between a sidewalk and a concrete house slab would cause either one to lift.

Still, I don't understand why that crack would cause anything to lift.  Water that gets into the ground will continue to sink into the ground until it gets down to the water table.  If that water were to freeze and expand, it could lift the sidewalk.  If you have a lot of clay in your soil, the clay would expand and lift the sidewalk, but one would expect that the clay under your sidewalk would already be wet since any moisture in it couldn't evaporate easily, and so adding water wouldn't result in any further swelling of the clay in the soil.  And, I see you live in Texas so the ground isn't going to freeze deep enough in winter to cause any significant amount of frost heave to lift either the sidewalk or the house.

I'm wondering if the smarter thing to do wouldn't be to just move the sidewalk away from the slab, or cut a few inches off the edge of the sidewalk and fill the gap with stones so that the sidewalk could move up and down independant of the slab, and just let it do that.

I guess I just don't see any reason why water leaking in between a concrete sidewalk and a concrete house slab would cause either one to lift unless that water freezes.  Did you're foundation specialist explain how that could happen?


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## Wuzzat? (Mar 3, 2010)

Foundatio said:


> where a side walk running along the slab is coming apart from the main slab, allowing water to go directly under it and push it up.


http://www.fairfaxcounty.gov/dpwes/publications/lti/expansivesoil.pdf

http://www.springerlink.com/content/1516886676l6qj77/

?


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## Foundatio (Mar 3, 2010)

Wuzzat? said:


> http://www.fairfaxcounty.gov/dpwes/publications/lti/expansivesoil.pdf
> 
> SpringerLink - Journal Article
> 
> ?




I'm sorry but I don't understand.


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## oldognewtrick (Mar 3, 2010)

Foundatio said:


> I'm sorry but I don't understand.



Dont worry, your not alone.


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## Nestor_Kelebay (Mar 4, 2010)

Foundatio:

Is the sidewalk slab beside your house actually lifting?

There is a crack you can see.  And, it would stand to reason that water could get into that crack.  But, do you see any evidence that the sidewalk slab is lifting?


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## Foundatio (Mar 4, 2010)

There is a visible crack. It's pretty big and getting bigger. I think the previous owner had issues and sealed it.


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## itsreallyconc (Mar 5, 2010)

if there's wtr penetrating, we'd probably use either polysulfide or 100% silicone installed to seal the jnt but it sounds as if there's also some expansive soils issue too,,, hydraulic has its +'s but, where there's movement due to expansion/contraction, it'll fail to accommodate the chang's.

we've got some commercial property ' managers ' who think we get frost in the ground here in atl    but its the heat that's hard on our conc,,, no provision for its expansion = much work for us    bless their hearts !

ps - don't forget - sealing a jnt/crk w/proper mtl = NO 3-SIDED adhesion, ONLY 2 ! ! !  depth:width ratio's extremely important, too !


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## Wuzzat? (Mar 10, 2010)

Foundatio said:


> I'm sorry but I don't understand.


Sorry.  

It's an article on expansive soil, which is probably what is causing your problems, and an article on remedying it by mixing the soil with lime and fly ash.


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## itsreallyconc (Mar 10, 2010)

how was it sealed - hydraulic OR caulk ?  most don't properly seal even IF they do pick the correct material & do the proper prep,,, just a thought


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