# Slab 'foundation', NO FOOTER! What to do?!



## n9viw

The short of it is just as the subject line says. The long of it is below.

Pony and I moved to this wonderful piece of the MOzarks last year, it's a mixed blessing. Part of the mix is the house- 32x36', originally intended to be a garage, the POs (NOT the original builders) started turning it into a house, and we're continuing in that vein. 
The only trouble is, the slab was poured with NO FOOTER, not a bit! At a couple edges, I can stick my hand UNDER the slab. But it gets better: rather than grading the site, the OB leveled it with... creek gravel. It's like pea gravel, but slipperier! So there's no real ground anywhere under it, except maybe at the highest point.
Needless to say, it's been slithering out from under the house for the last few years, and the foundation has substantial cracks and settling. I'm loath to do any major work on this place until I'm sure it's not just going to shift in a rainstorm and collapse on us!
I considered mudjacking, but there's really nothing against which the hydro-mud can push without just displacing gravel. Also considered having the house jacked and having a footer cut under it, but at that much cost, I may as well have the whole foundation removed and have a basement dug under the house! And in the 'zarks, that's a mega-pricey proposition (we don't have soil, we have 'dirty rocks'.) Not in the budget of time or space to strip it and start over, we have to work with what we've got.

Any recommendations?


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## Darren

Grout still seems like the best solution. How thick is the slab?


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## n9viw

Slab appears to be 8-10" thick, depending on where you measure. OB made 'forms' by hammering 2x2 into the ground (not far enough) and putting plywood against it, then lining with plastic. Of course, the cement pushed on the 2x2s and plywood, bowing them out, so the finished slab curves outward- it's about right at the corners, but along the sides, the foundation sticks out from the wall about 3 or 4 inches.


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## NorthwoodsMike

One idea, spoken as someone who isn't a foundation expert, would be to dig around the peremeter, 2 feet deep, 1 to 2 feet under the slab. I would then drill holes from the bottom into the existing slab, and use (what I think is called) hydraulic cement to fasten rebar into those holes so it hangs into the void. This void would then be filled with concrete, essentially turning you foundation into a monolithic slab. I'm not sure how mud jacking works, and whether this would occur before or after the concrete pour, but the voids under the slab could be filled in, including the areas with the gravel. The new "footing" should contain everything, especially if any grading issues are corrected.

After doing this, I would wait, and allow any final settling to occur. Then, I would install Gypcrete(sp?) to level the floors inside. Consider a few rolls of pex at this time too, heated floors are the best


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## NorthwoodsMike

I just had another thought. You could dig straight down from the foundation edge, 2-3 feet, and install 2 or 3 inch foam. Backfill with a really heavy clay-rich soil, and mudjack the voids. It essentially does the same thing i described above, less the structural support value-it keeps what is under the slab, under the slab. As with above, proper grading and drainage would be critical.


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## NamasteMama

Those type of foundations are the norm in my area.:bored:


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## fishhead

Could you fasten the bottom plates to the slab? At least that way the house and the slab wouldn't move at different speeds.

Or maybe dig around perimeter and pour a footing attaching it to the slab with rebar put through holes in the slab? Even if it was only done on one side it should anchor the slab.


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## TNHermit

n9viw said:


> Slab appears to be 8-10" thick, depending on where you measure. OB made 'forms' by hammering 2x2 into the ground (not far enough) and putting plywood against it, then lining with plastic. Of course, the cement pushed on the 2x2s and plywood, bowing them out, so the finished slab curves outward- it's about right at the corners, but along the sides, the foundation sticks out from the wall about 3 or 4 inches.


if the slab is 8-10 inches thick then you have the footer included in the slab as one pour. There are probably rod in that part. Most likely you never et a frost that deep that stays.
check it out. Dig under the slab about two foot back and see if it doesn't get thinner.
as for the gravel that is a good thing. you don't want dirt underneath. the more the better. i have a 4inch slab 30 x 60 in my shop over 6 inches of No 6. its been there for 15 years and has one small crack in it.


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## dirtman

I believe TNHERMIT is probably correct about it being a monoslab. If not then 8 to 10 inches of concrete would be like one giant footer. With the gravel beneath it there is nothing for frost to push against. You have to find a way to keep it from coming out from under the slab. Cracks are normal. The settling is the only thing that would concern me. Hydro-jacking would need something solid to push against and that would compromise the drainage the gravel is providing.


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## NorthwoodsMike

What does the grade look like around the house? While having gravel under the foundation, is nice for drainage, ideally, it should never need to drain because the grade around the house should have everything pitched away from it, and water shouldn't be coming through the roof 

I really think a containment perimeter(like the foam and clay backfill) followed by mudjacking and proper grading would solve any problems. The mudjacking would fill the gravel voids, but good grading and clay backfill would keep water out, eliminating the need for under slab drainage.


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## Evons hubby

I would just dig down about 1 1/2 feet all the way around the perimeter, about 8 inches wide and pour concrete up to near the level of the top of the existing slab. That should stabilize everything. 

ETA: be sure to slope the top of your new footer slightly away from the house to prevent water draining back under the house.


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## Pony

I've wondered if there was a way to build a containment wall to hold the gravel under the slab... you know, just dig in a bit, slap in some pressure-treated 1 or 2x8 boards, fill in the gravel...?

Dunno. Just want to get this project moving forward again.


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## motdaugrnds

Sounds ot me as though you have a nice thick slab for your house to sit on. The only problem appears to be it was not given any "lips" to keep it from sliding.

Now I've only learned masonry work by doing it on my own place; so take what I say with this in mind: I would fix this the simple way, i.e. put lips on the slab to stop it from moving, like Ivonne's Hubby said. The only thing I would add is: I would bring those lips up higher than the slab up about 6" up the sides of your house, making sure your house siding is "over" that lip so as to keep water from getting in it.

Then I would redo the "inside" floors of the house, leveling the floors and connecting the new flooring to the old flooring with small pieces of rebar (hiding the top of this rebar under your new layer of flooring). This is essentially doing the same thing to your house as you did to that slab, i.e. putting a lip on it that helps fortify the walls.

None of this would cost much; but would require some work.


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## n9viw

Well, in my mind, the problem is the fact that, rather than digging the dirt down to grade and THEN pouring a slab, they dumped a load a creek gravel on an unlevel surface and leveled THAT, then poured the slab on the loose gravel. Since the ground slopes somewhat under the gravel, it's all washing out. Reminds me of the comment in scripture about building one's house on rock vs. shifting sand... Oy!

I like the ideas of digging the perimeter out and pouring a proper graded footer, and tying it to the slab with rebar. Heck, at that point, I'd have a solid connection to earth; I could either jack the slab edges up, or just wait for the gravel under the house to slither out and settle in the vacancy of the gravel I'd dug out from the edges, and the floor will self-level! Double bonus.


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## davel745

I suggest you dig down about 2 feet and about 18 inches wide and but in rebar two on the bottom and two on the top and make sure you tie the corners in with rebar. if you don't use rebar the footer will crack and roll under.  I suggest you make the box that holds the slab as strong as you can afford. Then if it moves it wont break. Good luck


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## n9viw

Dave, thanks for the tip, I'll add that to the pile. I hope the slab doesn't pitch while I'm digging under the edge; do you think I should do it one edge at a time, or try to do them all at once?


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## Nicole Irene

How about extending out your house a couple of feet (extra sq footage!)? Then, new edge footing ( I would guess 18" deep x 12 in wide min, but I live in Ca and am not familiar with your state codes..a local structural engineer could give you the residential standard for your area), new 2-4 ft wide slab tied horizontally into existing slab with epoxy rebar. That way, you are not digging under your slab. 

Otherwise, you could pour a new footing in 4 foot sections if you need to dig out. Just tie into the slab with epoxy rebar.


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## davel745

n9viw said:


> Dave, thanks for the tip, I'll add that to the pile. I hope the slab doesn't pitch while I'm digging under the edge; do you think I should do it one edge at a time, or try to do them all at once?


If you cast the footer all at once it will be the strongest.


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