How To Use Pipe Dope to Prevent Plumbing Leaks
Updated: Jan. 31, 2024
Wondering if you should use pipe dope on your plumbing projects? We explain what it is and when to apply it.
Time A few hours
ComplexityBeginner
Cost$10-$20
Introduction
When I was new to the trades and learning to work on old, ramshackle plumbing systems, I noticed some pipe unions came apart far easier than others. Those showed signs they had been installed with sealant, and disassembling them required less grumbling on my part.
A more experienced plumber taught me to use Teflon tape and pipe dope. But over the years I've heard all kinds of material referred to as pipe dope, and the definition can be hard to understand for anyone new to DIY work.
I asked Matt Little, a licensed plumber and co-founder of Damien McEvoy Plumbing, to help us understand what pipe dope is and how to best use it during DIY repairs.
We'll start by going over the basics, then walk through how to apply pipe dope, step-by-step.
What is pipe dope?
According to Little, "pipe dope refers to a paste-like material that is used to seal and lubricate threaded pipe joints."
Some manufacturers call their product pipe dope, while others stick to the more formal term: pipe joint compound. Even worse, other manufacturers simply label it pipe sealant, which can cause confusion.
"Although pipe sealant and pipe dope are frequently used interchangeably, there is a distinction," says Little. "Although not all pipe sealants are pipe dope, pipe dope is one kind of pipe sealant."
A good example of a non-dope pipe sealant is PTFE tape, commonly called Teflon tape, which is wrapped around male pipe threads before being joined.
What is pipe dope used for?
"To seal and lubricate threaded pipe joints," says Little. "It is especially helpful, in my opinion, in preventing leaks and corrosion in plumbing connections."
In an ideal world, pipe threads would always align perfectly, and pipe dope and other sealants wouldn't be needed. But real-world variances means there can be imperfect contact between the mating threads. Adding pipe dope prior to assembly fills those minute voids between the threads.
Pipe dope also acts as a lubricant and prevents seizing of the mating parts, allowing for much easier disassembly.
When should I use pipe dope?
To ensure a tight seal with a metal threaded pipe, or easy disassembly later on.
"When working with threaded pipe fittings and connectors, I usually use pipe dope," Little says. "It works well to create a tight seal, whether using gas, water or other substances."
I asked about all those old pipes I worked on that came apart so easily. How does pipe dope prevent the pipes from seizing up? "Even after drying," Little says, "pipe dope keeps its pliability, enabling disassembly if necessary."
When should I not use pipe dope?
Not all pipe dopes are intended for all materials. Check the instructions on the sealant for a list of recommended materials. Connections that use a rubber gasket to make a seal (like a flexible sink supply line) don't benefit from dope, since the seal happens with the gasket rather than the threads. Plus, the solvents in some dope might damage the rubber gasket.
Tools Required
- Rag
- Wire brush
Materials Required
- Pipe dope
- Teflon tape (optional)
Project step-by-step (6)
Double-check the pipe dope directions
Always check the directions on the pipe dope to verify it’s safe to use on your project.
- Look for a list of approved materials or materials to avoid, along with an operating temperature range.
- Some pipe dopes use solvents that can damage plastics like ABS.
- Examine the pipes themselves to see if there are cautions against pipe dopes or other sealants.
- I’ve seen these warnings on sprinkler systems.
Clean the pipe threads
This is particularly important when reassembling older systems.
- Make sure both sets of threads are free of dirt and debris.
- Use a wire brush to clear away any buildup from the male and female threads.
- Wipe down threads with a rag if you see oils or moisture on them.
Apply sealant tape to male threads (optional)
Teflon tape and pipe dope work on their own, but some plumbers prefer to use both.
- Apply the tape clockwise when looking at the opening of the pipe so it will be tightened when securing the pipe.
- Don’t apply more than two to three turns of tape. You have to leave space for the pipe dope as well. Don’t add so much material that you bind the threads.
Apply pipe dope to male threads
- If the pipe dope has a brush or spatula integrated into the lid, use it to spread a layer of dope over the male threads.
- Squeeze pipe dope that comes in a tube onto the threads, then spread by hand or with a separate brush.
- If you put thread tape on the pipe, apply the dope in the same direction as the tape (clockwise when looking at the end of the pipe) to avoid loosening the tape.
- Cover the thread grooves with an even layer of dope.
- There’s less concern about putting on too much dope. The excess will squeeze out of the joint and be easily wiped away.
Connect the pipe
- Screw the male threads into the female fitting. Don’t over-tighten.
- Wipe away any pipe dope that squeezes out of the pipe.
Frequently asked questions
Why is it called pipe dope?
The exact origin is unclear, but I found stories indicating DOPE is an old plumbing mnemonic checklist. `D’ reminds us to check for the displacement of pipes,`O’ for obstructions,`P’ for a pneumatic pump to test for air leaks and `E’ for equipment testing.
Interestingly, emergency room and intensive care unit personnel also use DOPE as a post-intubation checklist. The seventh edition of the Advanced Trauma Life Support (ATLS) manual tells the story of doctors overhearing plumbers going through this checklist, and deciding to use it themselves.
I couldn’t confirm this is where pipe dope gets its name, but it was too interesting not to share.
Is pipe dope permanent?
Technically, no.
It provides a seal until the pipes are taken apart — no need to refresh it periodically. But it’s not permanent like glue or PVC cement is permanent. Pipes held together with pipe dope should still come apart.
How long does pipe dope take to dry?
A few hours, according to Little, though that can vary. Some pipe sealants never fully dry.
Is pipe dope better than Teflon tape?
Now we’re into what Little calls “the timeless dispute.” Either will work. It boils down to individual preference. “Both are good,” Little says, “but I prefer pipe dope because it’s simpler to use and works better to seal joints.”
I use pipe dope, but my go-to is Teflon tape. I find it tidier and I’m more likely to have it on hand.
About the expert
Matt Little started his career as a plumber. The co-owner of Damien McEvoy Plumbing, Little provides customers with valuable tips and tricks to keep their homes and businesses in top condition.
