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.