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Thread: Concrete coming tomorrow 3" pipe and flange on the outside

  1. #1
    DIY Junior Member joallen001's Avatar
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    Default Concrete coming tomorrow 3" pipe and flange on the outside

    I have concrete being poured tomorrow and have a 3" pipe that will need a flange. I know they make 3" flanges that go on the inside but I would rather put it on the outside of pipe. What is the best way to wrap the pipe so room is left for the flange to be glued on. I was thinking something like foam pipe insulation and melting it out with a torch after the pour. I am a little afraid the foam may push in to far with the concrete weight. Just trying to save myself from having to chisel it out later. Any suggestions on this? Also is a flange with stainless steel the best to use on a slab pour? I am staying away from the all plastic flanges!

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    In the Trades Gary Swart's Avatar
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    You're on the right track with the outside fitting flange, and SS is always preferred over all plastic. Go to a building supply house, even a big box store probably will be OK, and get the foam sleeve that is made for the purpose.

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    Moderator & Master Plumber hj's Avatar
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    Default sleeve

    They make foam sleeves and also wrapped corrugated cardboard ones. You just "pick" them out after the concrete is poured, you DO NOT "melt" them out. Don't do like a homeowner here did years ago. He formed his area and then called for the concrete to be delivered. He told his wife to have them pour it inside his form. A few hours later the concrete company got a call. He said, "You delivered my concrete 4 hours ago and it is still in a big pile. When does it level itself out?"
    Licensed residential and commercial plumber

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    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    We use a 4"x 3" 90 with 4" pipe coming through the slab. Then you can get a flange the fits inside the 4" pipe.

    John

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by hj View Post
    He said, "You delivered my concrete 4 hours ago and it is still in a big pile..."
    At least they got the slump right, eh?!
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    Forum Admin, Expert Plumber Terry's Avatar
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    We use a 4"x 3" 90 with 4" pipe coming through the slab. Then you can get a flange the fits inside the 4" pipe.

    John
    I like doing that too. That way I can cut it flush with the finished floor and glue it inside the pipe.
    Also with a 4", if the plumbing gets bumped I have some leeway that I don't get with 3"

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    Moderator & Master Plumber hj's Avatar
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    Default flange

    quote; glue it inside the pipe. I ALWAYS use a flange that slides OVER the outside of the riser. That way I can cut it off AFTER the flange is against the floor.
    Licensed residential and commercial plumber

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    DIY Senior Member DavidTu's Avatar
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    Quote Originally Posted by Terry View Post
    I like doing that too. That way I can cut it flush with the finished floor and glue it inside the pipe.
    Also with a 4", if the plumbing gets bumped I have some leeway that I don't get with 3"
    Terry, I don't follow... how does 4" provide leeway? It would seem if the pipe is not positioned correctly the 3" inside flange is also not going to sit correctly??

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