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Thread: Can I just use silicon to install a toilet flange?

  1. #1
    DIY Member petrie's Avatar
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    Default Can I just use silicon to install a toilet flange?

    I have a 4" pvc pipe that is flush with the basement floor surrounded by concrete. The toilet flange goes inside the pipe. So, what I'm wondering is being as water would have to shoot back up the pipe on the way down to try and leak out could I use silicone? Would silicone eventually fail and let sewer gase up?
    My concern is that I don't want to someday have to replace a flange and try and cut the old one out and reattach a new one.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Use a "good" flange now and you will not have to replace it someday. DON'T use silicone to attach it.
    Licensed residential and commercial plumber

  3. #3
    DIY Member petrie's Avatar
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    you said the metal ringed plastic flange is much better than the all plastic one right?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The flange should be set after the finished floor is in so that it sets on TOP of the FINISHED floor and is tight to the floor. It should also be anchored into the floor. You can do that with lead anchors, Tapcons, or inserts and screws. Assuming you are adding tile, when cutting the tile to fit around the flange hole, notch the tile so you don't have to drill through them to make the holes for the anchors...much easier either on the tile saw, or with a diamond blade on a grinder before it is set.

    The all-plastic flanges tend to be fairly thick, and some toilets don't like that, plus, they aren't as strong - knock the toilet, and you may break an all plastic one; or, tighten the bolts too much, and they break out of the all plastic one. The metal ringed ones (SS, not painted steel) are lower profile, stronger, and you can adjust them to get the anchor slots for the toilet where you want them before you bolt the flange to the floor. You'll need both some primer and pvc cement. The primer cleans the pipe, softens and roughs it up some, then the cement literally melts the surface, and when you slide the two together, the pvc 'welds' itself into a monolithic, watertite bond. Hold it together for a bit while the solvent dissipates, or sometimes the joint will push itself apart since the fitting is tapered. Wouldn't hurt to either immediately screw it down, or set something on top for it to solidify fully. Nothing more annoying than coming back and finding you've not got a 1/4" gap under it because it pushed itself back up and it's now solid as a rock!
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Member petrie's Avatar
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    I'll make sure I get the stainless steel ringed toilet flange for my project. What is the big downside to just siliconing it to the pipe? Like I said before the flange goes in the pipe so It shouldn't leak water. (or does water come up into the joint when you flush?) since it's anchored to the floor the only concern in my mind would be sewer gas coming up into basement. My whole concern is that with the trouble I had putting in the pipe and cementing it in I don't want to ever have to do that again. Would silicone including RTV eventually break-down and let sewer gas come up the pipe?
    Glueing it with PVC glue is standard practice so I should probably just do that, but I'd like a definetive answer why it would be dumb to silicone it. thanks.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    If there ever was a backup in the drain, you'd have more than sewer gasses trying to get out. Silicon isn't forever...a pvc bond effectively is.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    In the Trades Gary Swart's Avatar
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    I think you've missed the explanation jadnashua gave about how PVC works. It is NOT a glue in the normal sense. By liquifying the surfaces of the pipe and fitting, it actually makes a chemical weld when the two surfaces blend. Silicon is more or less a traditional glue.

  8. #8
    DIY Member petrie's Avatar
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    Sounds like it's unanimous. I'll use primer and pvc cement. Thanks

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