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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

2 Answers

up vote 8 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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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
Dupont would prefer you not call it Teflon tape. – Jeremy Stein Nov 29 '12 at 4:33
up vote 0 down vote

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
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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