Anaerobic sealants seal rigid metal-to-metal flanges. Gaskets bridge larger gaps and dissimilar materials. That raises a practical question in assembly planning: can you use an anaerobic sealant together with a conventional gasket? In most cases the two are alternatives, not partners, and combining them creates problems.
What Each Method Is Designed to Do
- Anaerobic sealants: liquid or gel adhesives that cure in the absence of air and the presence of metal ions, forming a rigid thermoset seal that fills microscopic imperfections between close-fitting metal surfaces. They act as a formed-in-place gasket and add structural stiffness to the joint. They suit precision-machined, metal-to-metal flanges.
- Traditional gaskets: pre-formed compressible materials such as fiber, rubber, or cork that fill larger, less precise gaps by compressing under bolt load and conforming to surface irregularities. They suit dissimilar materials, wider clearances, and joints that are opened frequently.
The General Rule: Anaerobics Replace Gaskets
On rigid machined metal flanges, anaerobic flange sealants are used instead of cut gaskets. As a gasket eliminator they:
- Prevent the relaxation and re-torquing that compressible gaskets need over time.
- Improve joint rigidity by filling the entire void between flanges.
- Reduce inventory, since one product replaces many pre-cut gasket sizes.
- Seal microscopic leak paths that a solid gasket can miss.
Why Combining Them Usually Fails
Putting an anaerobic sealant and a compressible gasket in the same joint is generally counterproductive:
- Inhibited cure: the anaerobic sealant needs metal-to-metal contact and oxygen exclusion. A non-metallic gasket between the flanges blocks the metal ion contact and can trap air, leaving the sealant partly or fully uncured.
- Compromised gasket function: a rigid cured film interferes with the designed compressibility of the gasket, so the gasket cannot seat and seal as intended.
- Disassembly damage: uneven partial adhesion can tear the gasket and mar the mating faces during future service.
- Redundancy: you spend on two solutions for a job one is designed to do, adding cost and assembly steps with no benefit.
If you are using an anaerobic liquid gasket, you are replacing the pre-cut gasket, not supplementing it.
What Happens Inside a Combined Joint
Picture a compressible fiber gasket coated on both faces with anaerobic liquid, then bolted between two cast flanges. The gasket holds the flange faces roughly a millimeter apart, so almost none of the anaerobic material sees metal contact. Air trapped in the fiber keeps the inhibitor active. When the joint is torqued, the gasket compresses unevenly because pockets of gelled adhesive resist where the material happened to touch metal at a bolt boss. The finished joint has neither the full clamp stability of a formed-in-place seal nor the even compression the gasket was designed for. Under thermal cycling it tends to weep at the low-contact zones first.
The Rare Exception
A very thin, non-curing anaerobic liquid used as a gasket dressing is occasionally applied with a rigid, non-compressible gasket in specialized static applications where fluid resistance on the gasket surface is critical. This is outside standard practice and requires material compatibility checks and manufacturer consultation. For the common case of a compressible gasket, the combination is inappropriate.
Selecting between a formed-in-place sealant and a gasket comes down to flange rigidity, gap size, and material mix. Email Us to review your joint with Incure’s technical team before you commit tooling.
Choosing the Right Approach
Choose an anaerobic flange sealant when you have rigid machined metal flanges with small, precise gaps, need strong leak prevention and added stiffness, and face high pressure, vibration, or aggressive fluids. Typical uses include gearbox casings, pump housings, and hydraulic manifold connections.
Choose a traditional gasket when gaps are larger or irregular, you are joining dissimilar materials or thin stamped flanges, the joint sees significant thermal movement, or frequent disassembly is a design requirement. Typical uses include valve covers, thermostat housings, and inspection covers.
How Incure Supports Sealing Strategy
Incure helps assess flange design, materials, operating conditions, and disassembly needs to determine the right sealing method, then guides product selection, surface preparation, and cure. Consider a plant planning to run a gasket and an anaerobic sealant together on a new pump: the better path is a single high-strength anaerobic flange sealant matched to the machined casing, giving a reliable seal and simpler assembly. Where a flexible seal is needed on stamped sheet metal, an RTV silicone is the correct choice instead.
For related guidance, see how thermal expansion mismatch causes bond and seal failure and our comparison of adhesive strength for heavy-duty repairs.
Key Takeaways
Do not combine anaerobic sealants with compressible gaskets. Assess whether your joint is rigid metal-to-metal with a small gap, or larger and more forgiving, and select one sealing philosophy accordingly. Consult data sheets for gap and temperature limits, and seek technical guidance when the choice is not obvious.
Contact Our Team for help selecting a sealing solution for your assemblies.
Visit www.incurelab.com for more information.