# Concrete Slab repair for plumbing trench



## dshap1984

I've just cut several trenches (2-3 ft wide x 25 ft long) in my existing concrete slab to run plumbing. The slab was about 4in thick with wire mesh and a plastic barrier between the concrete and the wet clay like soil (home located in New Orleans). I also had to break up footings in a few locations as well. I used a concrete saw to score the trenches and then a jack hammer to break the concrete. Most of the trench edges have 1-2 inches of smooth saw cut with the rest of the edge jagged. The plumbing is done, and now I'm ready to repair the slab.

I was planning to use a company that mixes short loads of concrete on site and then I would wheel barrow and poor the concrete. A few questions.

Do I need to put wire mesh?
Do I need to dowel into the existing slab or would adhesive painted on the edges be adequate?
Do I add a plastic barrier over the PVC pipe/below the concrete.

The plumber dug the trench out after I removed the concrete, placed the pipe, then back filled with the hard clay like soil (very clumpy). It appears like he mashed the clay like soil manually, but nothing else was done to compact it. It is pretty hard and doesn't move much when I stand on it. Is that ok or is it critical that this is compacted better? If so, any recommendation how without messing up all the plumbing slopes already installed.

Thanks,
Dan


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## Colbyt

It should have been filled with gravel and your plumber should know that.

I would either do it right or compact what you have using a hand tamper, but not over the pipes.


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## dshap1984

Thanks. I could try to dig up around the sides of the pipe and put gravel. What size gravel should I use?


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## Colbyt

I don't know the name of it. It is small and settles into place for pipe support. Also used for slab support and spread by the slinger trucks. Ask at the quarry, they will know what the slinger guys buy. A $10 trailer / pickup load should do the whole job.


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## Bondo

dshap1984 said:


> Thanks. I could try to dig up around the sides of the pipe and put gravel. What size gravel should I use?


Ayuh,.... The finer it is, the easier it is work work with, 'n compact,....

3/4" minus is a good grade,....


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## concrete_joe

that whole floor is non load bearing to the structure above. unless you are putting something real heavy on these areas where psi is high, i would simply wet that stuff and then hand tamp the best you can, then std 1" 4kspi concrete. i would however try to add back some vapor barrier, kinda hard with pipes there, but drape it and cut slits for vertical sections of pipe, etc.


i myself might drill some dowel holes in edge of that existing and then with some gorilla glue (just to keep them from moving) stick some 1/4" steel pins in there, 1" in and 1" out. 

other than that, keep going, it will be fine.


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## dshap1984

Thanks. I planned to pour the concrete this weekend. If I were to wet the mud and manual tamp it today/tomorrow, do i need to wait a period of time before pouring the concrete or can I just pour the next day?

You are correct, there should not be anything too heavy on this slab. Normal foot traffic in in a home. There will be a bath tub on one portion of the new concrete.


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## TheEplumber

I agree with concrete_joe, just go real easy on the water. Too much and you'll have a mess that will set you back.
Try tamping first, but be very careful not to lift the pipes as you tamp- it's easy to do.
Dowels at about every 4' can't hurt either


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## ron45

I'm hoping that's not your plumbers idea of a drain pipe.?
How much fall do you have.?

If you do plan to go with that, It's called pea stone....


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## stadry

dig that **** outta there so you can get 4" of conc placed onto a properly compacted base,,, YES to vapor barrier IF the rest of the floor also has it OR your replacement conc will suck moisture while the balance of the floor doesn't,,, no wire - its a pita & does little good,,, you'll need to score joints otherwise the conc'll crk all by itself where it wants :furious: #57 stone is what we use IF we need stone - compacted dirt base is usually good enough

btw, LESS water makes for better conc :thumbsup: why wet the base - there's plastic, remember ?

gorilla glue ? :huh: never thought of that,,,,,,,,,,,,,,,,,,,,,,,,, :laughing:


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## dshap1984

ron45 said:


> I'm hoping that's not your plumbers idea of a drain pipe.?
> How much fall do you have.?
> 
> If you do plan to go with that, It's called pea stone....


 
The plumber said he gave me atleast an 1/8 in per foot. Both the laterals switch from 4inch to 3, so he picks up an inch of slope without noticing on the top of the pipe.


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## dshap1984

TheEplumber said:


> I agree with concrete_joe, just go real easy on the water. Too much and you'll have a mess that will set you back.
> Try tamping first, but be very careful not to lift the pipes as you tamp- it's easy to do.
> Dowels at about every 4' can't hurt either


The clay like back fill he placed is really hard. I tried tamping it down and it doesn't budge. You can slam your heal of you boot into it without it depressing at all. 

You think it's fine to fill right over that stuff?
Also, the distance between the top of my slab and the top of my pipe is only 1-1.5 inches at spots. I know he didn't have much of choice to get the propper slope on the pipe. Would wire mesh be helpful to preven that narrow part from cracking?


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## concrete_joe

ron45 said:


> I'm hoping that's not your plumbers idea of a drain pipe.?
> How much fall do you have.?
> 
> If you do plan to go with that, It's called pea stone....


so OP - what does a bubble on a level look like when you put level on the drain pipes (the horizontal pipes). looks like tub and sink water can run, what about toilet? interested in seeing what a level bubble looks like.


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## SeniorSitizen

I would not leave that gumbo crap dirt in there. That looks as if it came from a ditch. 

Pictures can be deceiving but it looked to me in some areas the pipe was actually above floor level. Regardless, with it being that shallow I would be putting curved reinforcement there extending several inches over into the thicker mix and probably just a good mixture of grout in those areas thin areas. I don't think you'll like rock there.


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## concrete_joe

it looks clay like, probably will turn very hard when it dries out, which is fine here. 

OP - was that fill brought in or was that the dirt that was dug out?


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## Bondo

concrete_joe said:


> it looks clay like, probably will turn very hard when it dries out, which is fine here.
> 
> OP - was that fill brought in or was that the dirt that was dug out?


Ayuh,.... 1st post says it's native soils,...



> *The plumber dug the trench out after I removed the concrete, placed the pipe, then back filled with the hard clay like soil (very clumpy). *It appears like he mashed the clay like soil manually, but nothing else was done to compact it. It is pretty hard and doesn't move much when I stand on it. Is that ok or is it critical that this is compacted better? If so, any recommendation how without messing up all the plumbing slopes already installed.


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## concrete_joe

Bondo said:


> Ayuh,.... 1st post says it's native soils,...


doesnt say where it came from. if that dirt was under the original slab then that dirt is ok to go back but needs to be tamped some, etc. slightly wet, easy tamp, let dry 24hrs, pour new concrete.


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## dshap1984

To confirm the dirt is all the native soil that was below the existing concrete slab and an existing waterproof barrier. It was dug up, the pipe place on top, and manually compressed, not sure if they used a tamper or just pushed it down with shovel, boot, etc. 

I tried to compress it, but it would not compress much at all. I'll try to wet it a bit first, and then compress it.


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## dshap1984

SeniorSitizen said:


> I would not leave that gumbo crap dirt in there. That looks as if it came from a ditch.
> 
> Pictures can be deceiving but it looked to me in some areas the pipe was actually above floor level. Regardless, with it being that shallow I would be putting curved reinforcement there extending several inches over into the thicker mix and probably just a good mixture of grout in those areas thin areas. I don't think you'll like rock there.


 
I'm not sure I understand your suggestion with the curved reinforcement and grout. Can you please clarify? The top of the pipe is 1-1.5 inches from the top of concrete in a few areas.


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## concrete_joe

so you broke the original vapor barrier. the plumber should have placed plastic down 1st and tucked it under the edges of the existing slab, then some dirt, then his pipes, then fill.

if you cant tuck plastic under now that all that dirt is there and hard, i would drape some plastic over all that before new concrete, tuck plastic tight against the edges of the existing cut slab, pour concrete keep plastic sticking up at all the cuts, let dry, then cut the extra plastic flush to floor. the use of a few dowel pins is recommended.

water will migrate via path of least resistance, thus i would not pour new w/o some plastic there.


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## MTN REMODEL LLC

Seems to me you sort of have two competeing/contradictory objectives..

1)I would sure want some vapor barrier BUT

2) With a bare 1/8 fall, even though you think that clay is compacted well, I'd sure want any slab plumbing encased in concrete... and a vapor barrier will restrict concrete flow on the underside of your drains. 

Maybe overkill ideas but you might:

Mix a couple if bags of pea concrete or grout and pack the underside of your drainage as a pad... then poly over that.

Or put some kind of support (broad based chairs) under critical high points of your drainage.... then poly

I'd dowel some and use a bonding agent on your existing slab.

For your 1.5 pour over your high pipe, I'd use a pea gravel (pumping or bag) concrete... maybe add some fiberglass (if your final floor will be finished or your don't care about the fiber finish.

Are the 5 gallon cans your shower/tub boxes... never thought of that...

Good luck


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## concrete_joe

+1 on post #21


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## ron45

When it's all said and done keep this in mind......You can even put it behind a wall.

https://www.youtube.com/watch?v=YkeRtNvv6gY


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## concrete_joe

that saniflo unit, wonder how it holds up to a kid flushing a toy that has metal pieces in it?? or maybe flushes a golf ball?


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## ron45

Okay Joe, what did you do.?


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## concrete_joe

well, kids see those bowl commercials where they flush toys and golf balls and the toilet doesnt clog, imagine a golf ball entering that sani-flo unit. i can see how that conversation goes, "_no billy, you go upstairs and use that toilet, this one is for adults only_"


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## stadry

:huh: how does even an adult get a golf ball thru a shower drain ? ? ? :whistling2:


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## jomama45

stadry said:


> :huh: how does even an adult get a golf ball thru a shower drain ? ? ? :whistling2:


Now I'm really fearing growing old. Are you telling me that you start $*itting golf balls when you get older??????/ :laughing:


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## stadry

i'll let you know,,, we're playing 18 tomorrow :yes:


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