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Thread: Attaching Kerdi to old CI concrete floor

  1. #1
    DIY Junior Member DIYMom808's Avatar
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    Unhappy Attaching Kerdi to old CI concrete floor

    This project is truly wearing on me and before I throw in towel and call a plumber I was hoping to get some advice.

    The house we bought was built in 1965. The master shower has been leaking since we bought the house 4 years ago, this year we decided enough was enough and tore it apart. We love the neoshower shape and don't want to do too much to change what already exisit. What we are doing is putting in a new Kerdi shower base and will put up Hardi plank walls that we will Kerdi over before tiling with Fossil Stone Tiles. We've viewed the Kerdi DVD and understand that the Kerdi system must be attached to a PVC pipe from the drain. However, the DVD never discusses what to do if the drain is pre-exisiting and in the concrete floor. My husband removed the old mud shower pan and now we have a clean concrete floor with an old cast iron drain. We attempted to add the Kerdi to the drain but the Kerdi system is wider than the pre-exisiting drain. At this point we are not sure what to do. John Bridges site doesn't provide much help for our situation, although the site does have great advice, and Schluter Kerdi reps aren't much help either.

    My question is: how do we widen the cast iron drain in the concrete floor without having to break through the concrete? Can the cast iron drain be chiseled away enough to attach the Kerdi Drain System to? Or if anyone has a better suggestion that doesn't start with breaking the cement I'd so appreciate it

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default drain

    Not sure how to answer you, since the Kerdi drains all show it being connected to a PVC trap and riser. That would not work with a cast iron pipe because there would not be any way to connect the two materials without having a leak. If that is the only connection Kerdi uses, then you have to break the concrete, cut off the cast iron riser, couple on a piece of PVC cut to the right length, and then glue on the Kerdi drain.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    The absolute best way to do this is to dig up the floor and replace the trap and maybe the trap arm depending on how old things are and how they look with pvc.

    The Kerdi membrane is designed to use thinset to the (fairly significant) area of the drain's flange. It requires an overlap of at least 2" in order to prevent a leak through the thinset.

    Before they developed the kerdi drain, they had a method to use the material in a clamping drain assembly. It didn't work anywhere near as well as the one they have now. The new drain also is really nice in that the grate can be moved when setting the tile to get a perfect horizontal placement, which normally allows you to get the tile to mate up just the way you want it to.

    My guess is that you didn't like the answer you got on the Tile-your-world website...they have a huge amount of tiling expertise, and don't like to second guess the manufacturer's research on what works. Kerdi is a system, and not using all of the parts voids the integrity of the system. It really isn't a huge effort to tear into that floor and do it right.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Junior Member DIYMom808's Avatar
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    Default

    Thank you for your advice. As much as my husband is fighting me on breaking the cement, it sounds like we will have no choice. Now the unfortunate task of telling my husband that it's time to get a professional.

    Thank you.

  5. #5
    Master Plumber master plumber mark's Avatar
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    Talking breaking cement

    hey....its fun to break up cement....

    you can really work out some stress doing it

    just think of someone or something in your past

    (like my ex wife) and just start wailing away

    with that sledje hammer....

    next thing you know your are done....

  6. #6
    In the Trades Gary Swart's Avatar
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    Default

    Breaking concrete really isn't as bad a job as it might seem. It doesn't require a industrial size jack hammer. You can rent rotary hammer/drills that are quite easy to handle and will do the job, or you can buy one for around $100. You do need to be concerned about safety and wear eye and ear protection and a dust mask is advisable. Since breaking concrete raises a fair amount of dust, you will want to drape plastic sheets around the work area.

  7. #7
    Homeowner geniescience's Avatar
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    Default What size is your CI pipe?

    Mom

    Can you measure diameters and post more information? Your existing drain in cast iron. You still have options to consider.

    Plumbers routinely connect pipes and things from different manufacturers. Once you define your situation more clearly, the plumbers here can direct you to a drain that works. In fact, all drains work.

    David

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