Replacing toilet flange - use 4" ABS as coupler?

Andy911 · Nov 26, 2010

Hi, I am trying to replace my toilet flange. There's not really any 3" pipe past the old flange before the 90, so my cut pipe right now is 3" I.D. and 4" O.D (ie. because it is the thickness of the original 3" plus the toilet flange coupling)

Can I use a piece of 4" ABS as a coupler and then a flange that fits inside 4" ABS? I would file down the inside of the pipe so there isn't a sharp edge for stuff to catch on as it's going down

Thanks!

Andy911 · Nov 29, 2010

Hi, I bought some 4" ABS and it fits like a glove around the existing (which is an abs 90 3" outside fitting - the old flange is inside)

I'm going to use this 4" to couple a new 3" outside flange unless someone knows why it would be a bad idea?

Thanks!

Sponsor · 2022-01-29T12:20:58-0800

Andy911 · Nov 29, 2010

Hi, I bought some 4" ABS and it fits like a glove around the existing (which is an abs 90 3" outside fitting - the old flange is inside)

I'm going to use this 4" to couple a new 3" outside flange unless someone knows why it would be a bad idea?

Thanks!

Gary Swart · Nov 29, 2010

Both ABS and PVC use what is termed, "interference fit". While the 4" pipe may seem to fitting nicely over the 3", it is not an interference fit. Both ABS and PVC are solvent welded, not glued in the usual sense of the term. This means the surfaces of the pipe and fitting is melted by the solvent for a few seconds while the materials are joined. The two surfaces then fuse together in a weld, very much like welding metal.

Andy911 · Nov 29, 2010

Hi Gary, I get what you are saying about "solvent welding" but I'm not sure what you mean about the 4" overtop not being an "interference fit"?

I guess - is a normal coupler slightly tapered inside in order to acheive the interference fit? If I use a generous amount of cement is this really that important?

If so do they make a specialty coupler for this application? (ie 4" I.D.) I suppose a 4" I.D. toilet flange would also not be tapered inside?

Thanks!

Gary Swart · Nov 29, 2010

You have the basic concept of the taper correct. The solvent used is not glue. ABS and PVC have different chemical makeup and their respective solvents are chemically different, but they both work the same way; they melt the surfaces of the pipe and fitting allowing the fusing of the two parts. These solvents will not fill a void. People often attempt to dry fit ABS or PVC drains only to have one or two problems. If they just slip the pieces together and cut pipe to fit the space, when they joint with the solvent, they find they lose about 1/4" or so per joint because the pipe was not fully seated in the fitting. If they try to force the pieces together dry with a hammer, the pieces still do not fully seat, but they have a near impossible task in separating the parts. I think if you take your problem to a plumbing supply house, they will be able to advise you on what you need. I'm quite sure there is a proper way to fit a flange to your drain.

Andy911 · Nov 30, 2010

I don't think there is a void - the pieces are quite snug - but do you mean without the taper it's not guaranteed to be void-free?

I'll call some plumbing supply stores but it's very difficult to explain what I want and up in Canada the choices are always more limited. I figured if anybody would be aware of something that exists it would be here.

Thanks!

Redwood · Nov 30, 2010

I would remove the old toilet flange coupling and use 3"

Andy911 · Nov 30, 2010

I am finding it impossible to gently remove the remaining bit of the old 3" flange inside the 3" closet bend, and I don't want to really start chiseling it and crack the ABS because its difficult to access even from below.

Redwood · Nov 30, 2010

Then hire a plumber to do it...
We do it often...

Andy911 · Nov 30, 2010

Yes if I could find someone who wouldn't charge a minimum service call then I would!

Redwood · Nov 30, 2010

Well I sometimes work on my van...
I enjoy playing mechanic and I'm not to bad at it...

But on that cold winter day, when a job will take to long, or, when it requires equipment or tools I don't have it goes to the mechanic and I pay what it costs....

Andy911 · Nov 30, 2010

Maybe so, but these forums are partly meant to be a DIY resource, and I'm still in DIY mode on this one. If I exhaust my possibilities on an outside coupling then I may need to hire someone, but I'm not there yet.

Redwood · Nov 30, 2010

It wasn't me that said this....

andy911 said:
I am finding it impossible to gently remove the remaining bit of the old 3" flange inside the 3" closet bend, and I don't want to really start chiseling it and crack the ABS because its difficult to access even from below.

So if you can't then it is on to Option B....
Paying the mechanic....

Gary Swart · Nov 30, 2010

You came to the forum with a legitimate question. When we could not give you the answer you wanted to hear, you tried to convince us to tell you your idea would work. Well friend, it won't. Yes, this is a place for DIY questions and where DIYers can get help in their projects, but you're not going to get a green light to proceed with an improper procedure. Some DIYers have some skills, others have little or even none, but we all have a point where what we are trying to do or what we want to do is either not possible or is beyond our individual abilities. At that point, the best advice we can offer is to hire a professional. Your problem is one that a plumber can solve quickly and correctly. Of course, you can always "glue" the 4" over the 3", what the hell do these guys know...they are just trying to line their own pockets. Do what you want. You asked for free advice, you got free advice and apparently you don't want to take it. Well, that's OK, you're not required to.

Andy911 · Dec 1, 2010

Whoa - I didn't mean any offence! All I was saying is that I'd still like to see if I can track down some kind of specialty coupling that might work for my situation.

I suppose some kind of Fernco-type coupler is out of the question?

Sorry again if it seemed like I was ignoring your advice - far from it! I'm just a little stubborn is all

Cheers

Redwood · Dec 1, 2010

No offense was taken here...

I was just pointing out the logic I was walking into with answering this post.
The "I can't do it myself, yet i don't want to hire a plumber." is tough place to bring a plumber that is trying to help you on a DIYer Forum.

The only good way at this point is to remove the old flange completely and cement on a new one preferably an ABS flange with a stainless steel ring. This is really the the only way that your problem can be reliably repaired without opening below. It is what we would do when confronted with the same job because any other method would leave a liability for leakage in the future and damage to the ceiling below, wood rotting and mold.

Andy911 · Dec 13, 2010

Well I spend yesterday afternoon doing this the right way - I used my multitool to cut off as much of the old 3" pipe as possible, then use my rounded edge rasp to file the rest of the pipe down. 3 hours later

Good as new! (Well, I had to lop about a 1/4" off the closet 90 but I still got a good seal).

Here's the part that sort of steams me a little bit - I noticed the wax rings all come with a built in plastic flange - the throat on these is only 2.5" wide ie. smaller than a cheater flange! So I do ask myself what was the point of going through all that hassle....

Cheers!

Redwood · Dec 13, 2010

Well many of us don't use that style of wax ring because they have a long history of creating more problems than they ever solved.

Now your mention of trimming 1/4" off the 90 has me wondering what you did there...

It doesn't sound good...

Andy911 · Dec 13, 2010

All the big boxes around here sell nothing but the wax rings with the plastic insert though...

What I meant was that I trimmed off the old 3" flange spout but I cut a little further ie approx. 1/8" to 1/4" of the closet 90 off - just due to error in eyeballing where the 90 began. So there isn't the full coupling of a brand new 90 but I left enough that it got a good solid fit. The fit was extremely snug and the toilet flange is very well screwed to the subfloor - it ain't going anywhere

Replacing toilet flange - use 4" ABS as coupler?

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