A persistent drip at a threaded iron or brass joint usually stems from one error: misunderstanding how tapered national pipe threads seal. Unlike compression fittings that seat against an internal rubber gasket or copper ferrule, National Pipe Taper threads wedge directly against opposing metal threads. To prevent micro-channels of pressurized water from escaping along the helical root, you need a thread sealant that lubricates assembly while filling imperceptible manufacturing voids.
How PTFE Thread Tape Actually Functions
PTFE tape is primarily a thread lubricant rather than a glue, allowing you to turn threaded male fittings deeper into female sockets without galling the metal. For clean shower arm replacements and small brass nipples under forty pounds of pressure, three wraps of standard white PTFE tape wound clockwise will seat cleanly. Wrap in the direction of the threads so the tape edge does not unravel and bunch up when screwing the joint together.
When Pipe Dope Becomes Strictly Mandatory
Liquid thread sealant, commonly called pipe dope, contains suspended curing compounds that fill uneven thread profiles where tape might tear or shred. On larger diameters over one inch, or on rough cast-iron and natural gas lines, paste forms an elastic barrier that will not migrate or blow out under thermal cycling. Always verify that the paste compound lists potable water certification on the label before brushing it onto domestic supply lines.
The Double Seal Rule for Brass Valves
For critical installations like water heater nipples or primary pressure regulators, trade practice combines both sealants for foolproof reliability. Begin by wrapping the clean male threads with two passes of high-density tape, then smooth a light coating of pipe dope directly over the tape surface. This dual-barrier method fills voids completely while keeping cleanup fast and preventing excess paste from washing into your aerators.