Pipe Dope

Pipe dope (formally called pipe joint compound or pipe thread sealant) is a paste applied to the male threads of a pipe connection before assembly to fill voids in the thread engagement, preventing water, gas, or steam from leaking through the threaded joint. Unlike PTFE tape (plumber's tape), which is a solid wrap, pipe dope is a viscous paste that fills gaps more thoroughly on coarser or damaged threads.

Types of pipe dope

• Standard (non-hardening): the most common type — stays soft and workable, allowing disassembly later. Good for water and low-pressure steam lines. Brands like Rectorseal T Plus 2 are industry standards.
• Gas-rated: specifically formulated and tested for use on natural gas and LP gas lines. Never use a water-only compound on gas threads. Look for "gas-rated" or listings under ANSI/UL standards.
• PTFE-enhanced: paste blended with PTFE particles for additional sealing. Works on most metals and plastic threads.
• Hard-set (anaerobic): cures by polymerizing in the absence of air (like thread locker compounds). Provides maximum seal but requires special removers to disassemble.

Pipe dope vs. PTFE tape

Both are thread sealants but suit different applications. PTFE tape (plumber's tape) is preferred on fine threads, brass-to-brass connections, and any joint you may need to disassemble. Pipe dope is preferred on steel pipe, coarser NPT threads, corroded or slightly damaged threads, and connections subject to vibration. Many professional plumbers apply PTFE tape first, then a thin coat of pipe dope over it — especially on gas lines and threaded steel pipe.

Application

Apply pipe dope only to the male (outer) threads, not the female (inner) threads, to avoid pushing compound into the pipe. Use a brush or your finger to coat all threads. Assemble hand-tight, then wrench-tighten 1–3 additional turns (NPT threads taper, so they seal through engagement, not torque). Wipe off excess. Cure time before pressure testing: 1–2 hours for most non-hardening compounds.