# Concrete backfill of slab after plumbing repair



## Msradell (Sep 1, 2011)

You definitely want to put out a vapor barrier, tape it to the existing barrier on each side to get the best deal possible. Putting in rebar probably is going to help money for a trench area that small although it wouldn't hurt. How deep are you going to pour the concrete?

Mixing in a 5 gallon bucket with a drill may sound like a good idea but you probably are going to have cold joints between every batch because you won't be able to mix it fast enough. Cold joints are going to cause future problems. I would definitely use bonding agent, some people say it helps some people don't but it's not very expensive so why take the chance.

If you don't use rebar you may be better off buying some of the concrete mixes that contain fiber reinforcing in them.


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## miamicuse (Nov 13, 2011)

When I initially made the slab cut, I used a 7" diamond blade saw. It was able to cut through the 4" slab in some spot and not in some others, and a sledgehammer was used to break things loose. After I got removed the broken concrete the existing vapor barrier was torn, ripped in many places. It is impossible to tape new barrier to old. I backfilled the soil and wet/compacted as I go. To try and tape the new barrier to old I would have to remove some soil to expose the underside of the perimeter of the trench to make room for me to try and tape. In some cases I may have to reach 2", 4" or more to get to the old torn edge of the old barrier. That would create a sliver of void under the old concrete edge unless I pack those with new concrete.


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## stadry (Jun 20, 2009)

{B}a 7" blade on a circle saw will only usually cut 3" deep,,, you don't need to o'lap the existing v/b - just come close to it,,, even the bag your suit came in when you picked it up at the cleaners,,, or 3mil trash bag,,, you can mix in a 5gal bucket too,,, just 'rod' the new conc into the previous bkt & you'll be fine,,, bonding agent on the existing ? maybe but not on the previous bag of conc
we'd use the yellow bagg'd conc, NOT the 5000
if you're taking that long to mix conc, you shouldn't be doing the work :vs_no_no_no:


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## miamicuse (Nov 13, 2011)

I have a somewhat crazy idea which is to actually carry the bags of concrete mix right into the trench, and mix them in place with a shovel. The width of the trench is just about right for a shovel moving around, could I not use a garden hose to wet the concrete, mix them in place without a messing with a wheel barrow and spilling and making a mess?

The only issue would be the vapor barrier may be ripped by the shovel...but if I cut a piece of thin plywood and lay it on top of the barrier, lay the bags of mix on top, cut and remove the bag, hose down and mix, I can use a mudmixer right in the trench and a shovel to even things, and when it's done I can reach down there to pull out the piece of plywood? Of course if I use rebars then this will not work.


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## stadry (Jun 20, 2009)

*works fine for fence posts but what happens when the woods rots & there goes the support for the conc ?*


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## miamicuse (Nov 13, 2011)

stadry said:


> *works fine for fence posts but what happens when the woods rots & there goes the support for the conc ?*


My thinking is the plywood will have drilled holes where I will have a few ropes tied through the holes. Then the plywood would lay in the bottom of the trench, and I unload bags of concrete mix into the trench, add water into the mix with a garden hose or bucket, mix with a shovel.

Once I am done I pull on the ropes to drag the plywood out.


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## Nealtw (Jun 22, 2017)

miamicuse said:


> My thinking is the plywood will have drilled holes where I will have a few ropes tied through the holes. Then the plywood would lay in the bottom of the trench, and I unload bags of concrete mix into the trench, add water into the mix with a garden hose or bucket, mix with a shovel.
> 
> Once I am done I pull on the ropes to drag the plywood out.


Put the concrete in the wheel barrow in the back yard mix it and dump it in a 5 gal pail and deliver. No dust in the house.:vs_cool:


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## jlhaslip (Dec 31, 2009)

Lay the plywood on the floor right beside the trench and mix it right where you need it.


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