Two types of thread joint
- Thread that seals: tapered threads (for example a radiator valve tail into the radiator). The thread itself needs a sealant — PTFE or paste.
- Thread that only clamps: parallel threads with a washer or olive. The washer or olive is the seal. Tape here does nothing and can even stop the washer seating.
How to wrap PTFE tape properly
- Clean the thread.
- Hold the fitting with the thread end pointing at you.
- Wrap clockwise — the same way the nut will tighten — so tightening does not unravel it.
- Pull slightly tight so the tape sinks into the threads.
- Use 5–10 wraps; thicker for loose threads.
Pro tip: If the tape bunches up or tears as you screw it in, you wrapped it the wrong way. Start again.
When paste is better
Jointing compound fills gaps well and stays flexible. Many plumbers use a little on olives to help them seat, and on threads for heating systems. Always use a product approved for drinking water on water supply pipes.
Gas tape vs water tape
Yellow tape is made for gas. We teach plumbing only — never work on gas. For water, use white WRAS-approved PTFE.
