Should the dope be applied directly to the male threads or should the tape go on first?

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    Use one or the other, not both. Frankly, I've never heard ANYONE suggest using both, and have never seen anyone do this, and I didn't even fathom there would be debate about this. Personally, I typically use dope for metal fittings, and tape for plastic, but it's not set in stone. Using too much tape OR dope with plastic can cause the fitting to break, and certainly that's a bigger concern if you have both. – gregmac Nov 29 '12 at 19:33
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    @grecmac some casual googling will turn up plenty of people recommending to use both. – Matthew Nov 29 '12 at 22:04
  • Note: A discussion on chat caused this related question to be opened: diy.stackexchange.com/questions/21117/…. FWIW, no one else had ever heard of using both. – gregmac Dec 3 '12 at 17:31
  • Ive heard of a lot of guys using both (personally pipe dope alone is all I use). Really wont hurt to use both just makes whomever does this method feel like they have a better seal – user15447 Oct 5 '13 at 20:57
  • Go on what? Context, please. – isherwood Dec 29 '15 at 15:28

11 Answers 11

up vote 11 down vote accepted

If you're using both, the tape would go on first. Which is immediately evident, if you've ever tried to apply them the other way round. There's open debate over whether or not there are any advantages to using both products together, or if each product by itself is adequate.

Pipe dope

Pipe dope; also known as pipe joint compound, is used to seal and lubricate the threads of a threaded pipe joint. It's available for both water and gas lines. It's applied by simply brushing it on the male threads of the pipe joint, before the joint is fit together. Pipe dope never hardens, and will not crumble and fall out of the joint.

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Teflon Tape Dope

Teflon Tape dope; also known as polytetrafluoroethylene (PTFE) Tape, or thread seal tape, is also used to seal and lubricate the threads of a threaded pipe joint. It's available in high-density and low-density flavors, for water and gas pipe. PTFE tape is applied by wrapping it in a clockwise direction, around the male threads of the threaded joint. PTFE tape is available in color coded versions (pink for water, yellow for gas), as well as the common white variety.

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  • 2
    Just glancing quickly through International Plumbing Code (IPC), I noticed for threaded joints of various materials it says "Pipe-joint compound or tape shall be applied on the male threads only". Notice it doesn't say "and/or"... Just sayin' – Tester101 Nov 28 '12 at 20:55
  • yes, but I have widely read advice about using both. I've also used both with success. I was just curious if there was a "right" way to do it... and I didn't think of the fact that it doesn't make sense to put dope on before tape – Matthew Nov 28 '12 at 22:40
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    Dupont would prefer you not call it Teflon tape. – Jeremy Stein Nov 29 '12 at 4:33
  • Dupont will have a lawyer call you and explain that Teflon® is a registered name as well as Viton® and that in order to not dilute the trademark, you must refer to it as Tape made of Teflon® or Seal made of Viton®. Joke is that we used the manufacturer's description on the seals and I highly doubt they called Parker-Hannafin to tell them to revise all their manuals. Explained all the Aeroquip manuals where they referred to all this hose stock as Stainless Braid with tube of Teflon® – Fiasco Labs Oct 5 '13 at 21:43
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    I love that we have a discussion of why not to call it Teflon, but not one explaining why it's called "dope" instead of the name on the package - "compound". – DaveM Jan 11 at 3:49

Im only here because we argue about it at work all the time. I originally worked for a sprinkler company that put dope then teflon on, and thats how we did it, and if you didnt do it that way, you were simply doing it wrong, without a specific reason given. I then went to a company who did it the opposite way with again no believable reason given. I've never had a leak with either method so I don't think it really matters all that much. but since dope is supposed to be applied to male threads, I would prefer it be put on first, and then the tape has something to stick to when first applying it. Also it is much cleaner to handle that way.

At the end of the day I don't think it really matters, and if your pipes arent holding water it's not because of the tape or the dope, but rather the guy threading the pipes or wrenching them in. If you're breaking female fittings simply because you have teflon on the pipe, then you either need to pay greater attention when wrenching on the fitting or adjust your die head.

If anyone can come up with a scientific reason why one goes before the other, I would love to hear it.

  • 1
    That's exactly my feeling too, this should be a matter of objective scientific testing and not really opinion. But maybe such research, if it exists, is not widely available or is proprietary. You'd figure any company selling these products has to know very clearly what they can claim about it in marketing, packaging, etc. without risking getting "in trouble" (ie sued). – DaveInCaz Mar 22 at 9:39

Many people frown on tape being used for gas piping. If the fitting was ever taken apart for service, shreds of tape can travel to gas valves, etc. Gas controls with shreds in them may very well not be covered by the warranty. Also, putting pipe dope on the male only keeps dope from being pushed into the system. Wiping any from the end will help. If the fittings leak they are probably just some of the cheap junk you can buy today, or someone locally ran the pipe tap/die in too far. As taps/dies are tapered that will oversize the female or undersize the male thread.

Use tape first, then apply the pipe dope on top.

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    What?? Why? I've NEVER seen this done, and can't imagine any need to ever do this: both products have the same ultimate purpose. I typically use dope on steel and brass fittings that I'd use a a big wrench on, and tape on plastic pipes. I see no benefit whatsoever to using both, and in fact, I'd say it's more likely to cause problems than doing it properly with one or the other. I'll remove my -1 if you can update with a good rationale, but just saying to use both is bad advice in my opinion. – gregmac Nov 29 '12 at 19:29
  • I was actually just answering the question that was asked by the OP (before Tester101 put is more complete answer up). I have never used both at the same time but I have read advice from those who do use both (and starting with the tape and then the dope). As @Tester101 stated above it does look like the IPC does not recommend using both. – auujay Nov 29 '12 at 21:46
  • I don't see why this warrants downvotes. If this answer presumes that I am going to use both, as I stated then his answer is perfectly valid (albeit not as complete as others) – Matthew Nov 30 '12 at 0:11
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    It's not a good answer in general since it provides no reasoning or citations as to why this might be correct. Normally I would just not upvote, but answering like this is implying the original question is valid, and I don't think it is (and I'm by no means alone, judging from responses of other users and this question). – gregmac Dec 3 '12 at 17:40
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    The goal is to not have leaks people. Apply the tape, add a little dope and tighten the pipe. Then, wipe your threads to clean the joint so it looks nice; display some pride in your work. It is NOT rocket science. I've had joints with no tape or dope that haven't leaked because I know how to set up my dies. But going to sleep at night knowing there's no leaks is comforting, so stop complaining about the right way and just use both!! – user46780 Dec 18 '15 at 5:22

Put on some high density yellow or pink Teflon tape, then a thin layer of Rectorseal Tru-Blu. I have had good luck with this dope. DO NOT use low density Teflon tape or non setting pipe dope, in my experience it does not work as well. Only apply pipe dope lightly with a BRUSH, not a shovel.

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    Why do you recommend using both types of dope at the same time? Is there an advantage to using both together? – Tester101 Jun 25 '14 at 10:51

A long time ago, when I installed gas lines for furnaces, using both was the approved method of the contractor that I worked for.

We used one to one and a half turns of Teflon tape, and then doped the threads of the gas line(s).

The reason as explained to me was that the tape sealed it, and a light doping lubricated it to make putting it together easier, as well as aiding in the seal of a more poorly machined fitting.

I've rarely had to use both on a plumbing fitting though. Only on a stubborn old fitting or two that were leaking with tape alone.

I'd use t-tape first and a small amount of pipe dope on the tape.

I've worked on 30 inch water main breaks And have installed hundreds of copper water services with brass fittings,fire hydrants ive taped live water mains worked on cla- Val's installed 10" gate valves, PVC plumbing. Installed thousands of water meters and customer shut off valves. 15+ years of plumbing outside of working for a water department for 10 years.

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    Did you use tape and dope together in all of those situations? – BMitch Feb 19 '16 at 13:36

I find that on pvc fittings if tape is used it can crack the female fitting .I use dope only on pvc and tighten only as needed .not saying it should not be done but I find a tendency for that to happen

It's all relative. If you were dealing with three-quarter inch PVC or DWV of any kind obviously you just need Teflon. When you are dealing with plumbing, and heating systems in particular, you will want to use both. Teflon first. Dope second. The last thing you want to do is complete a job (especially big commercial) and have a leak in the system. Working in the fields for decades I can tell you I've seen far less leaks down the road on fittings that have both.

Teflon tape should never be used for gas piping unless it is yellow rated.

  • You make no case for using both other than an anecdotal assertion. They have the same in tended purpose, and you basically create a third point of failure (pipe:tape, tape:dope, dope:pipe) for absolutely no reason. – isherwood Jan 10 at 21:10

I've always used dope over the tape because it acts like an anti seize lubricant in the event you have to take it back apart in the future.

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    So does the tape. It's a primary selling point of Teflon. The whole idea of using both furrows my brow, since the dope would be sealing to the tape, which makes no sense. – isherwood Jan 10 at 21:09

Using Dope and tape together is how it should be done.Dope has Teflon embedded in it and acts as lubricant and Bonds with the Teflon tape making a great seal.

For black iron 1 1/4 or larger, I dope, tape and then dope again.

Like one user has said. It’s the dye or the guy wrenching Them in.

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