# Digging UNDER poured concrete home floor?



## DYI hunting (Jan 10, 2012)

My great-uncle has one of those homes that is a single story built on a 8" poured slab with fiber impregnated concrete.  He has a water leak near where the water line comes in under the slab.  We have dug up the water line to the slab and not found the leak, but we can see where water is coming from somewhere under the house slab.  He  insists we dig a tunnel under the slab following the pipe and assures us the 8" foundation would hold up fine.  He is a pretty head strong 73 year old who would rather dig it up himself than do anything different. There is no way to convince him to hire an engineer or contractor, we have all talked till we are blue in the face.

I am a bit concerned, concrete and dirt coffin comes to mind.  With wet dirt, we would have to dig a little wider to keep the sides from collapsing and I don't know if 8" of concrete even with fibers would hold up to digging out 4 or 5 foot of dirt under it.  And wouldn't the floor crack over time since we could never pack the dirt back as firm as it is now?


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## gtparts (Jan 10, 2012)

Not interested in taking on the job, but there are only two practical solutions.

(1)
Remove concrete directly above the water line and wide enough to work on it when you expose the leaking portion. Repair line.  Back fill. Re-pour the concrete.  Pretty? No. Labor intensive? Yes. Expensive? Could be.

(2)
Run new line from outside to inside, connecting to the interior water system, eliminating that portion that is leaking under the slab. Pretty? If properly designed and installed, it will be "pretty". Labor intensive? Less so than tearing up the concrete. Expensive? Is anything cheap these days? But, it will probably be cheaper, quicker, and cleaner than option (1).

Best wishes on dealing with the great-uncle, the water problem, or both.

Is "backing out the door and burning rubber" an option?


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## skiff23 (Jan 10, 2012)

I think 8 " of concrete will hold up. I have done this before. 
On the other hand, there are plumbers who can come in and locate the leak within a sq ft or so and fix the problem. his choice. 
 But  I do think 8 in of concrete will hold uo just fine. Heck I even saw them dig up a complete house , pad and all , and move it down the road. So dig on......


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## atwenterprise (Jan 10, 2012)

I agree with GT. Option 2 is the best bet. I have done many of these in slab homes with frozen lines or defective polybutylene piping. Much cheaper to run a new line and be done with it. Has your great uncle talked to his insurance company?


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## thomas the redneck (Jan 10, 2012)

skiff23 said:


> I think 8 " of concrete will hold up. I have done this before.
> On the other hand, there are plumbers who can come in and locate the leak within a sq ft or so and fix the problem. his choice.
> But  I do think 8 in of concrete will hold uo just fine. Heck I even saw them dig up a complete house , pad and all , and move it down the road. So dig on......


i agree and have seen it done too
but i can think of no one on this earth that i like/love or think enough of to crawl under  their for at some point in time i will be surrounded by dirt with a slab of conceat over my head


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## groundhawg (Jan 10, 2012)

skiff23 said:


> I think 8 " of concrete will hold up. I have done this before.
> On the other hand, there are plumbers who can come in and locate the leak within a sq ft or so and fix the problem. his choice.
> But  I do think 8 in of concrete will hold uo just fine. Heck I even saw them dig up a complete house , pad and all , and move it down the road. So dig on......



Have done it twice to help fellow next door when we lived in FL, near Tampa.  Digging in the wet sandy soil was not to hard. First time we dug a "trench" about 4 by 6 feet under the kitchen and about 15 feet under the house.  Second time we dug a hole just large enough to wiggle in and out of about 8 to 10 feet under the house to a leak under his bathroom.


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## gobbleinwoods (Jan 10, 2012)

Hire a plumber to find the leak and cut through the floor and fix it.  From my building experience if there is a stub up close to the outside where  the leak is showing my guess would be the copper pipe has come in contact with the concrete and chemically reacted over time and presto a small pin hole leak.


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## swamp hunter (Jan 10, 2012)

If You can Tie into the Exsisting Plumbing from a Hole Drilled into the exterior of the Home at ground level ...Do that.
A Concrete Wet Saw of a Chipping Hammer inside the Home is a BIG MESS . I Know ...........


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## SGaither (Jan 10, 2012)

Do not attempt to dig under the slab. The slab is supported by the ground, the ground pushes up on the slab with the same force as the slab pushes down. When you remove the compacted dirt from a section you loose the slab's support in that particular area. Without an engineered slurry you would never be able to accomplish the same compaction under the slab and over time it will crack and fail. I've seen this happen with a ruptured water line that the flowing water excavated the soil beneath the slab thus causing a sink hole effect, this caused extensive damage to the exterior brick walls, interior sheet rock and obviously the slab.


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## jimbo4116 (Jan 10, 2012)

swamp hunter said:


> If You can Tie into the Exsisting Plumbing from a Hole Drilled into the exterior of the Home at ground level ...Do that.
> A Concrete Wet Saw of a Chipping Hammer inside the Home is a BIG MESS . I Know ...........



Re-plumb to the existing plumbing overhead with pex.  You need a plumber.


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## DYI hunting (Jan 10, 2012)

Going to put this mess off till the weekend and hopefully his daughter can talk him into using a plumber or going about it in some other method.  I doubt he will change his mind.

If we do dig under, can we backfill with concrete since we can't compact the dirt as good as it was before?


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## rider1009 (Jan 10, 2012)

I would not backfill with concrete, it shrinks as it sets. That would leave gaps. Grout is the only recomended backfill as it expands as it sets.


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## Tacoma (Jan 11, 2012)

Hire a plumber (with insurance) and fix it right.


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## dawg2 (Jan 11, 2012)

jimbo4116 said:


> Re-plumb to the existing plumbing overhead with pex.  You need a plumber.


I agree.  I would not dig more than a foot or two under that slab.  This can affect load bearing wall sand crack slabs, sheetrock wals, tiles, etc.



rider1009 said:


> I would not backfill with concrete, it shrinks as it sets. That would leave gaps. Grout is the only recomended backfill as it expands as it sets.



You can use hydraulic cement.  It will expand.


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## dwhee87 (Jan 11, 2012)

If you do end up digging it out, call the cement company and ask for a flowable fill. It's basically a concrete and sand grout, with no aggregate. It'll flow into the void spaces and set. All concrete companies make it.

My $0.02...if you only have to dig a foot or two, go for it, if it's further under than that, hire a professional.


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## DYI hunting (Jan 11, 2012)

Talked to his son today and looks like they might be willing to hire a professional.  But he still insists no one is going to cut holes in his floor.  I hope I am off the hook.  If they do, I feel sorry for the guy who tackles it.  I used to cut his grass, and he would supervise me and insisted on cutting the hardest parts so I didn't mess up his push lawnmower.  Gotta love the old man, he is a hoot.


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## MOTS (Jan 11, 2012)

I would have full confidence with an 8 inch concrete slab tunneling any amount of length if I was chasing down a pipe, 40 inches wide at the most? The Mexican cartel don't even use a concrete roof!


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## cb1967 (Jan 11, 2012)

*solution*

rest assured, i know nothing about nothing! however, jimbo4116 and gocargo strikes me as brilliant. i'm sure everyone has seen the big steel vertical walls they set in ditches to hold the dirt up while men work in them. there has been many men lost they're life in those circumstances without that piece of safety. you aint got enough money to send me under that house!


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## Ronnie T (Jan 11, 2012)

He needs a plumber.

Not a handy man.  A real life professional plumber.

It'll be cheaper.


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## sengdigger (Jan 12, 2012)

Up here our slabs are only 4" of concrete and the footer is 8" deep, so from the outside it looks like a 8" slab. I doubt that the slab is 8" except on the footer.


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## Confederate_Jay (Jan 12, 2012)

If he has copper pipes chances are another leak will spring up later even if he fixes this one. Re-pipe overhead and be done with it for good.


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## biggsteve (Jan 13, 2012)

Confederate_Jay said:


> If he has copper pipes chances are another leak will spring up later even if he fixes this one. Re-pipe overhead and be done with it for good.



exactly.  like faulty buried electrical cables, when there's a failure, another one is close by.  trust me.

i had a similar problem.  i put pvc up through the attic, then down to the kitchen sink.  still workin.  lol


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