# Erosion and a void around slab edge



## FreshFish (Mar 22, 2012)

Hello All,

I have lived in my house for four years and have slowly discovered that it has been pieced together over the years.

The side (right side in the drawing I attached) of the house sits on a slab with no footing.  When we moved in, there was some minor erosion around the slab edge and the chimney had a slight tilt - in four years, that hasn't changed (no new cracks in the chimney, no other visible signs of any settling - inside or out).

I noticed a few weeks back that some finish work around the rear corner of that side of the house was cracking.  I pulled it back to discover that there is also a slab back there, but this area has a nice-sized void under the slab edge.  There is probably a 3'x3' area of unsupported, 'floating' concrete.  The picture I included doesn't show that, but you can see the edge of the slab with darkness underneath.

Luckily, this part of my house is extremely light construction - a shed-style roof and a single story...so not a ton of weight.  But it obviously freaked me out.

I have received a few bids on different ways to fix everything (including the section with just the minor erosion and tilting chimney).  My problem is that everyone I have talked to has a particular product that they are trying to sell me.

The two basic options that have been presented to me are: 
1) Slabjack everything for a total cost of about $2000
2) Reinforce everything with a combination of slab piers and push piers for about $11000

I am looking for the right balance of cost and effectiveness.  I know that piers will solve the problem forever, but doesn't it seem like overkill for the areas that just have minor erosion that hasn't changed in 4 years?  And is slabjack a bad idea for large voids?

Also, I should mention that we can assume that the causes of the erosion (poor drainage) will be fixed by the time I get the foundation work done.  We are having a french drain installed that will get the water away from the structure.

Thanks for honest opinions!


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## nealtw (Mar 22, 2012)

I would go with slabjacking, if it's done right, it is effective.


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## joecaption (Mar 22, 2012)

Looks like a DIY enclosing an old slab open deck to me.
That T-111 should never had been installed that close to the grade. I'd bet if you opened up that wall there's going to be mold wet insulation and may even be rotted bottom plates.
Ever notice the inside floor getting wet when it rains, or at least a musty smell?


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## FreshFish (Mar 22, 2012)

@joecaption: you are right that it looks like an enclosed patio...

I haven't noticed any wet floors, but there is a musty smell when we get a lot of rain.  Oh Joy, sounds like it's time to open up some walls too.

Any opinion on the foundation fix?  It sounds like once it's all done I may need to do a different type of siding...


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## nealtw (Mar 22, 2012)

Good eye Joe. That would explain the house covering the slab. You may want to check all around the house for a foundation. If it is all like this you have no frost protection. Our slab type house still have a foundation to below frost level.


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## joecaption (Mar 23, 2012)

Where do you live? (It's a great idea to go back and add that info in your profile)
Reason I'm asking is it also looks like someone ran a water line through an outside wall. (I see a foam cap over a sill cock under the window)
Running lines through an outside wall is a big no no in a cold area.

There's a few things that can be done and still have that siding workout.
Any place the slab sticks out behond the siding needs to be cut off so water does not just lay there and seep in.
Change the roof framing so there's more over hang.
Add a gutter.
Go over the walls with Tyvex and add vinyl siding. Personaly the way I would do it is run a band of 1 X 6 vinyl lumber around the bottom of the wall that sits low enough so it's at least 1" passed the slab, a piece of Z moulding,
then J moulding then run the siding.
Not the perfect way but would stop the water from getting in between the slab and the bottom plate.
The


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## FreshFish (Mar 25, 2012)

Hi Joe, thanks for the feedback.  I am in Seattle, WA (I updated my profile too).  It does get pretty cold during the winters.

Thanks for the suggestions on the siding issues.

I should also mention (as it may have not been clear from the pictures/description) that there is a concrete 'walkway' just adjacent to the slab the house is on, but the two aren't attached.  I cut a strip out of the walkway (shown in the picture) just to be able to see under the house slab and assess the size of the void.  Eventually that entire walkway slab will be removed.

Thanks again,
Ben


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## nealtw (Mar 26, 2012)

The frost line is Seattle is 18", that means the bottom of the concrete should be 18" below ground level and you should have 8" of concrete above ground. Neither contractor was offering a good solution for your house. Normaly I would go with mud jacking and it will do the job but the house is still subject to frost heaving.


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## BridgeMan (Mar 31, 2012)

Jumping in a bit late here, but I have to ask--exactly why are you considering slab-jacking?  Is the interior of the house floor settled?  If the intent is just to fill the void under the slab shown in the photo, that's easy to accomplish by a DIYer at considerably less expense than what you were quoted.


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## Bridger51 (Aug 24, 2013)

BridgeMan - I'm with you.  I have a ranch style home in Florida that has the underside of the slab becoming exposed due to a the yard settling.  Along with that I need to build a new retaining wall, install gutters on the house, etc.  I plan to raise the elevation of my yard and fix those problems, but how exactly do I make sure all the air is removed from under my slab from the outside??  Today is the first time I noticed how bad it is.  Not more than 1 inch of air, but it goes back under the slab at least 1 foot.  Their are no current settlement issues inside the house and the slab has not cracked to my knowledge, but I'm getting nervous.  I have a few ideas, but an not positive on a few of the technical parts.  Can I use a poly compound myself?    This should be a DiYer....IMO.  BridgeMan if your out there, you seemed like this could be an easy fix.

I was thinking of using a loose concrete or poly and letting it settle under the house than burying that under the dirt, But do I have to keep everything from sticking out farther than the current slab?  Will only a couple inches laterally create different problems in the future?


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## nealtw (Aug 25, 2013)

BridgeMan said:


> Jumping in a bit late here, but I have to ask--exactly why are you considering slab-jacking?  Is the interior of the house floor settled?  If the intent is just to fill the void under the slab shown in the photo, that's easy to accomplish by a DIYer at considerably less expense than what you were quoted.


 A little late but the chimney leaning was the reason for the mudjacking.


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## BridgeMan (Aug 29, 2013)

nealtw said:


> A little late but the chimney leaning was the reason for the mudjacking.



Sorry, neal, but he didn't mention that he was trying to correct the slightly-tilted chimney by means of mud-jacking.  His concern was the large void under the slab, not adjacent to the chimney.


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## BridgeMan (Aug 29, 2013)

Bridger51 said:


> BridgeMan - I'm with you.  I have a ranch style home in Florida that has the underside of the slab becoming exposed due to a the yard settling. . . . . but how exactly do I make sure all the air is removed from under my slab from the outside??  Today is the first time I noticed how bad it is.  Not more than 1 inch of air, but it goes back under the slab at least 1 foot. . . .  Can I use a poly compound myself?    This should be a DiYer....IMO.  BridgeMan if your out there, you seemed like this could be an easy fix.
> 
> I was thinking of using a loose concrete or poly and letting it settle under the house than burying that under the dirt, But do I have to keep everything from sticking out farther than the current slab?  Will only a couple inches laterally create different problems in the future?



If all you're dealing with is only an inch of settlement, extending just a foot under the slab, why not go the cheap (and easy) way?  Which in my opinion would be dry-packing a pre-packaged concrete mix into the voided areas, working from the outside, and starting in the middle of any given void and working outwards to enable entrapped air to escape.  Hardest part would be hand-excavating temporary "work stations" in the adjacent soil, to provide space for working a tamper back and forth after you've dropped in a load of slightly-stiff (no more than 2" slump) concrete, preferably off of slightly-sloped, intermittent planks.  Installing the planks with gaps between them will provide room for working your tamper in a horizontal plane.  Use a 2 x 4 in the flat orientation for the tamper, rounding the edge you hold to avoid blisters.

Doing it this way is economical, probably less than $50 for bagged concrete, depending on the size and extent of your house's voids.  Ten 80-lb. bags of mud will cover almost 100 feet of voids around the perimeter of the house, assuming an average thickness of 3/4".  And there should be no extensions of your work beyond the existing slab, as you can finish the concrete flush with the slab edges with a hand float (resin or mag) if poured stiff enough.


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## nealtw (Aug 30, 2013)

BridgeMan said:


> Sorry, neal, but he didn't mention that he was trying to correct the slightly-tilted chimney by means of mud-jacking.  His concern was the large void under the slab, not adjacent to the chimney.


 
So let's go over the problem; A slab, maybe a patio or garage or carport, who knows, laid on dirt, soft dirt. If this was errosion, where did the dirt go.

It went down, settled, As the problem may have been isolated to this area and the void  is what needs to be dealt with mudjacking would fill the void and raise the slab back to level. As stated, that still leaves the problem of frost protection and no footing.
Was there something you wanted to add to that.


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