Anytime you are connecting pipes or fittings together, you almost always need to apply a thread sealant on the threads. That means having to choose between pipe dope and Teflon tape.
So, what is the difference between Teflon tape and pipe dope? Which one should you use? Is one better than the other?
Pipe dope is easy to apply, provides better sealing in permanent connections, prevents joint corrosions, seals and also lubricates threads but is messy and not good for plastic connections. Teflon tape is versatile, mess-free, used in plastic and metal connections but isn’t corrosion-proof.
In summary, when connecting plastic, soft metals, unreactive metals and small diameter pipes, Teflon tape is the thread sealant to use. On the other hand, use pipe dope when connecting natural gas pipes, large diameter pipes, steel and reactive metals.
I should however give a disclaimer that this recommendation is not by any code but rather from personal knowledge and experience. Plumbers are actually split in the middle on what thread sealant to use, some swearing by pipe dope and others by Teflon tape.
Pipe Dope vs Teflon Tape
When dealing with brass pipes or fittings, Teflon tape is preferred over pipe dope unless the connection has an O-ring or rubber gasket. Having said that, there is nothing wrong in using pipe dope in brass fittings.
Contrary to some people’s concerns, pipe dope can and is used in water lines. If anything, Teflon tape should be the main concern since it can tear off and clog faucet aerators and other orifices.
One thing that I have however observed is that most old plumbers use pipe dope more while younger plumbers prefer Teflon tape. The most important thing is to make sure that the connection does not leak afterwards.
There are plumbers who even use and recommend using pipe dope and Teflon tape together. Should you do that though?
Yes! You can use both Teflon tape and pipe dope together. Apply about 4 tight wraps of Teflon tape on the threads then apply the dope/paste on the Teflon. Always apply Teflon tape first then pipe dope on the tape and not the other way round.
Actually, about 40% of plumbers use Teflon tape and pipe dope together. There is however a good number of plumbers and other building professionals who insist there is no advantage of using Teflon tape and pipe dope together.
And they are not wrong. Both Teflon tape and pipe dope work excellently on their own. If you are however having leaks after using them separately, trying to combine them will not hurt.
Pipe dope is the best sealant for gas lines and is preferred to Teflon tape by most plumbers and inspectors since it’s thicker, seals better, lubricates and also prevents thread corrosion. If you must use Teflon tape, use the yellow-coded tape which is specifically designed for gas lines
In case you are wondering, plumber’s putty and pipe dope are not the same thing. Although both are used for sealing, plumber’s putty is a solid paste and is used to seal flanges while pipe dope is used to seal threaded connections.
Let us now look at Teflon tape and pipe dope separately and learn more about their properties.
Pipe Dope
Pipe dope, also known as pipe joint compound or thread paste is a putty-like adhesive that is used to create watertight and airtight seals in threaded connections. It comes with an applicator brush to help you spread it around threads.
Pipe dope is applied on the male threads but some people apply it on the female threads as well. A nice coat on the male threads is however sufficient to create a good seal and you don’t need to worry about damaging pipes since the excess dope is squeezed out at the top of the connections.
Apart from creating an airtight seal, pipe dope also helps with lubricating the threads, helping you to screw the pipes or fitting together easily, as well as when disconnecting the joint. That is the reason dope is used even in thread connections that do not need a sealant.
Pipe dope is the sealant of choice when connecting joints in metals that corrode easily. Unlike Teflon tape which can tear and subject the threads to corrosion, pipe dope does not allow agents that cause metal corrosion to come into contact with the threads.
Pipe dope is so easy to use but it is messy. You will need a rag to wipe off excess dope afterwards and also clean the applicator brush.
To apply pipe dope, swab a coat on the male threads making sure to cover all the threads using the applicator brush. You can then thread the male connection on the female connection being careful to avoid cross-threading then tighten with a wrench.
Teflon Tape
Teflon tape, also known as pipe thread sealant, PTFE or plumber’s tape is a thin film of thread sealant that comes rolled in a plastic groove.
Teflon tape may seem easy to apply but it actually isn’t until you learn how to. However, after learning how to use it becomes so easy to apply and unlike pipe dope it is mess-free.
With Teflon tape, you must know:
- Which way to apply it
- How much of it to use
- How to cut it
- Where to apply it
- Where not to apply it
Applying Teflon tape in the wrong direction or using too much of it will end up with the same problems you were avoid in the first place; leaks!
It is important to remember that Teflon tape should be applied in the direction of the threads. To tighten a connection, we turn the fitting clockwise. You should therefore apply about 4 wraps of Teflon tape on the threads in a clockwise direction from back to forth with nice overwraps.
What happens when you apply Teflon tape in the counterclockwise direction? As you thread in the pipe/fitting, the Teflon tape will be unraveling which means you will end up with no thread sealant in your connection.
On the other hand, using too much Teflon tape will mean that the fitting/pipe will have problems threading in the female connection, and you may use a wrench to persuade it. Needless to say, you will end up with damaged threads.
The main reason most folks have leaks after using Teflon tape is because they don’t know how to use. Check out this post on how to properly use Teflon tape.
Most Teflon tapes are white in color. These are excellent for use in water applications but if you want to use Teflon tape for black iron pipe (used for gas line), use the yellow Teflon tape.
The yellow Teflon tape works is premium high-density tape and that is why it is specifically designed for propane, butane and natural gas lines.
When to Use Teflon Tape and When to Use Pipe Dope
Why do we even need to use a thread sealant in the first place? And do you know that not all connections need a thread sealant?
The main reason we need to use a thread sealant is due to the fact that most threaded connections are tapered. That means that the threads at the front of the connection are smaller than the threads at the back.
As such, there are gaps between the major and minor diameter of the threads. That is where thread sealants come in.
So, where do you use pipe dope and where do you use Teflon tape? Both of these thread sealants are actually very effective and both will work in almost any situation but use the below guide if you are not sure:
Plastic pipes: Teflon tape. Since pipe dope is a lubricant, it can result in overtightening of the pipe causing thread damage or even cracking of the pipe.
Steel/reactive metals: Pipe dope. Steel and other metals that are prone to corrosion are better of connected using pipe dope. Apart from lubrication and sealing, the dope provides corrosion protection unlike tape.
Large pipe: Pipe dope. Whenever you are working with a large diameter pipe, pipe dope is easier to use that Teflon tape. This is however not to say you cannot use Teflon on big pipes. It is just simple that way.
Small pipe: Teflon tape. For the above reasons.
Gas lines: As I mentioned earlier, pipe dope is the thread sealant to use when connecting gas lines. It is actually a requirement in some states. Use the yellow-colored Teflon tape if you must use Teflon with gas line connections.
Wrap Up
And basically that is everything about pipe dope and Teflon tape. If you use both (separately) but still have leaks, you can try using them together.
Apply about 4 wraps of Teflon tape on the connection followed by a nice coat of pipe dope and see what happens.