If you’re accustomed to using PTFE (Teflon) tape to seal pipe threads and are tempted to use it with your flange sealant—stop immediately! The use of PTFE tape or any other non-metallic barrier on a flange joint is a guaranteed path to sealant failure.

The core issue is that PTFE tape, which is a polymer (plastic), completely defeats the two essential requirements for anaerobic sealants to cure:

1. It Blocks Metal Contact: Anaerobic sealants must touch bare metal for the metal ions to catalyze the cure. PTFE tape acts as a physical barrier, preventing this crucial chemical reaction.
   
2. It Creates a Gap: Even when compressed, the tape creates a layer that is often too thick, exceeding the narrow 0.25 mm gap tolerance of most anaerobic flange sealants. This increased gap traps more air (oxygen), which further inhibits the cure.

The result: The sealant inside the joint remains a liquid or semi-cured gel, leading to inevitable leaks under pressure.

The Fix: Anaerobic Sealants Replace Non-Metallic Gaskets and Tapes

The single best solution is to use the anaerobic sealant as intended—as a Formed-in-Place Gasket (FIPG) that replaces traditional sealing methods on rigid, machined metal-to-metal joints.

1. Remove All Traces of PTFE and Old Gasket Material

Thoroughly remove all existing PTFE tape, old pre-cut gaskets, and any residue from both mating surfaces.

• Clean: Use a sharp scraper or abrasive pad to get down to bare metal.
• Degrease: Wipe down the surfaces with a residue-free solvent to remove any oil or contamination.

2. Apply the Sealant Directly to Bare Metal

Apply a continuous bead of the anaerobic sealant directly onto one clean, bare metal flange surface, ensuring the bead encircles all fastener holes and fluid ports.

• Avoid Over-Applying: Use just enough material to coat the surface; excessive material will squeeze out and remain uncured (which is normal, but wasteful).

Incure HeatGrip™ 504 Flexible General Purpose Gasket Sealant

For most professional and DIY gasketing jobs, we recommend the Incure HeatGrip™ 504 Flexible General Purpose Gasket Sealant.

• Purpose-Built Replacement: This product is designed to replace the need for pre-cut gaskets, tapes, or traditional barrier methods on rigid flanges.
• Leak-Proof Seal: Its flexible cured layer effectively fills all microscopic imperfections on the metal surfaces, creating a 100% surface-to-surface seal that is superior to compression-dependent tapes.
• Reliable Performance: It withstands operational pressures and resists the chemicals and fluids (oils, coolants, etc.) common in industrial and automotive assemblies up to 150∘C.

Simply put: When using an anaerobic flange sealant like HeatGrip 504, the PTFE tape is not just unnecessary; it is actively counterproductive to achieving a proper, reliable seal.