How to Seal PVC, CPVC and PP Threads: Teflon Tape or Thread Sealant

How to Seal PVC, CPVC and PP Threads: Teflon Tape or Thread Sealant

Threaded PVC, CPVC and polypropylene (PP) fittings need a sealant on the threads to seal. There are two choices: PTFE thread seal tape, often called Teflon tape, or a thread sealant, also called pipe dope. Both work on plastic when the right one is chosen and applied correctly. Most leaks and cracked fittings come from an incompatible sealant, too much tape or overtightening.

Choose the Right Sealant

  • PVC and CPVC: use PTFE tape or a thread sealant rated for the material, never both on the same joint.
  • PP: Banjo does not recommend PTFE tape on its polypropylene threaded fittings, because tape enlarges the male thread and can split the female thread. Banjo recommends a pipe thread sealant such as RectorSeal Tru-Blu or RectorSeal No. 21.
  • Check thread sealant compatibility. Some pipe dopes can cause chemical stress cracking in plastic, so confirm the sealant is rated for your material. For example, RectorSeal No. 21 lists PVC but should not be used on CPVC or ABS.
  • Use PTFE tape at least 3.5 mil thick.

Before You Start

  • PTFE tape and thread sealant can be used on both Schedule 40 and Schedule 80 threaded fittings.
  • Make sure the threads are clean and undamaged.
  • Always follow the fitting and sealant manufacturers' instructions.

How to Apply Teflon Tape

  1. Apply tape to the male threads only.
  2. Start at the first full thread and wrap in the direction of the threads (clockwise when looking at the end of the fitting). Pull the tape snug into the threads.
  3. Use 2 to 3 wraps, covering the full thread length. Do not let tape extend into the opening.

How to Apply Thread Sealant

  1. Apply an even coat to the male threads, covering all threads.
  2. Do not apply excess sealant or let it clog the opening.
  3. On larger sizes, check whether the female threads should also be coated. For Banjo PP fittings, Banjo calls for coating both male and female threads on 1-1/4 in. and larger.

How to Tighten the Joint

  1. Thread the joint together by hand until finger tight.
  2. Finish with a strap wrench or smooth-jawed wrench:
    • PVC and CPVC fittings: tighten 1 to 2 turns beyond finger tight.
    • Banjo PP fittings with thread sealant: Banjo calls for hand tight plus 1/2 to 3/4 turn.
  3. Do not overtighten. PTFE tape acts as a lubricant, which makes a taped joint easier to overtighten.
  4. Do not back the joint up after tightening.

Prevent Split Female Threads

Overtightening a tapered thread creates expansion forces that can split a plastic female fitting. PVC Schedule 80 Special Reinforced (SR) fittings use an external reinforcing collar to contain those forces, which helps prevent split threads even if a fitting is accidentally overtightened.

Plastic Female Threads on Metal Pipe

When a plastic female adapter threads onto metal pipe, use 5 to 5-1/2 wraps of tape. SR fittings are also designed for direct connection to threaded metal pipe.

Threading Plastic Pipe

Only cut threads into Schedule 80 or heavier pipe. Do not cut threads into Schedule 40 pipe. Threading removes pipe wall, so fitting manufacturers apply a 50% pressure derating to threaded pipe. Check the system pressure before choosing threaded connections.

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