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Thread: Questions about back filling a hole in slab

  1. #1
    DIY Junior Member Will C.'s Avatar
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    Feb 2014

    Default Questions about back filling a hole in slab

    Just wanted to say Hi and yes I'm a newbie to this website. I've been reading different threads before posting to try and keep my questions to a minimal as I'm sure they are basic and everyone except me knows the answer! I'm replacing the drain below the slab in a shower and I have the cast iron pipe cut and ready to re install ABS.

    1. Which one or either should I use to connect the CI to ABS? the CI measured closer to 2.5" OD so not sure if I will be able to make the 2"-2" work. If neither of these are the type I need what would be a better option? pic 2

    2. I was told I could use the dirt on the right with minimal rocks to back fill the hole but didn't know if I could reuse the pile on left with more rocks? I have three buckets of similar consistency dirt on the right but will need another if the pile on the left doesn't work. I can pour the other buckets into my proper blue storage container if that will help? pic 4

    3.If I need extra refill would sand be acceptable or should I purchase it from a box store?

    thanks in advance for any advise and if my explanations don't make any logical meaning I will try to explain again!
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    Last edited by Will C.; 02-24-2014 at 08:15 AM.

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
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    2.5" OD is considered 2" pipe.
    Going from cast iron to plastic is easy with a no-hub type coupling. If you have the cast out of the hole, then you can see about matching up the sizing with the new coupling.
    Back fill with what you have there. You can also pick up a bag of sand if you're more comfortable with that.

  3. #3
    Test, Don't Guess! cacher_chick's Avatar
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    Jan 2008
    Land of Cheese


    After bedding plastic pipe in a trench, I surround it in coarse sand before backfilling with native soil, and then at least 3" of stone between the concrete pour and the underlaying soil. If you are doing a big area of concrete, you might also consider 2" xps foam board under the pour for insulation.

    Most companies such as Fernco make couplers specifically listed for connecting ABS to cast iron.

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