Two sealing products get used interchangeably on shop floors constantly, despite working on completely different chemistry — and picking the wrong one is one of the more avoidable causes of joint failure in industrial maintenance.
Two Different Technologies, Two Different Jobs
Flange sealants and gasket makers both create a formed-in-place seal without a precut gasket, but the similarity ends at the finished result. Anaerobic flange sealants remain liquid in air and cure only when confined between two mating metal surfaces, triggered by the exclusion of oxygen and contact with active metal ions. Gasket makers, most commonly RTV (room-temperature vulcanizing) silicones, work through an entirely different mechanism — curing when exposed to atmospheric moisture, producing a flexible, rubber-like seal rather than a rigid plastic one.
When an Anaerobic Flange Sealant Is the Right Choice
Anaerobic sealants are built for rigid, machined flanges with tight tolerances, typically handling gaps under about 0.25mm where the surfaces fit closely together. They excel at preventing vibration-induced loosening, since the cured sealant bonds the components together as a rigid, thermoset plastic rather than simply cushioning the joint. They also hold up well under high pressure without extruding, and offer strong chemical resistance to oils, coolants, and industrial solvents.
When a Gasket Maker Is the Better Fit
RTV gasket makers are the correct choice for non-rigid or uneven flanges — their flexible cure allows them to conform to irregular or stamped surfaces that an anaerobic sealant, which needs tight metal-to-metal contact to cure properly, simply can’t accommodate. They fill larger gaps than anaerobic formulas are designed for, flex with the assembly under vibration and thermal cycling rather than resisting movement rigidly, and work across a wider range of materials, including plastic, composites, and painted surfaces — not just bare metal.
A Practical Decision Framework
| Consideration | Anaerobic Flange Sealant | RTV Gasket Maker |
|—|—|—|
| Gap size | Small, precision gaps under 0.25mm | Larger or uneven gaps |
| Surface material | Machined metal-to-metal contact required | Metal, plastic, composites, painted surfaces |
| Flexibility needed | No — joint should remain rigid | Yes — accommodates movement and expansion |
| Disassembly frequency | Less frequent; cured bond is firm | More frequent; RTV is generally easier to remove |
| Operating pressure | High pressure environments | Low to moderate pressure |
Getting the Choice Right the First Time
Choosing based on gap size and surface rigidity first, then confirming pressure and disassembly requirements second, resolves most of the ambiguity between these two product categories. Applying an anaerobic sealant to a warped or stamped flange it can’t properly bond to — or using a flexible RTV on a precision-machined, high-pressure joint it wasn’t designed for — accounts for a large share of the sealing failures maintenance teams encounter. If you’re not certain which category fits a specific flange, our technical team can help you work through the gap size, materials, and pressure requirements — Email Us with the details of your assembly.
Thermal Cycling Affects Both Categories Differently
Rigid anaerobic seals and flexible RTV gasket makers respond differently to thermal cycling, which is worth factoring into the decision alongside gap size and pressure. CTE mismatch between dissimilar materials is a documented driver of seal and bond failure under repeated heating and cooling, and a rigid anaerobic sealant on a joint with significant thermal movement may need reconsidering in favor of a flexible formula that can accommodate that expansion instead of resisting it.
When Neither Option Fits Perfectly
Occasionally a joint falls between the two categories — a machined flange with a moderate gap that’s larger than an anaerobic sealant handles well but with pressure requirements higher than a typical RTV is rated for. In these cases, consulting the specific product’s technical data sheet for its actual gap-fill and pressure ratings, rather than relying on the general category description, is worth the extra step. Borderline cases are exactly where defaulting to whichever product is already open on the bench causes the most avoidable failures.
Selecting With Confidence
Neither flange sealants nor gasket makers are universally “better” — the right choice depends entirely on gap size, surface material, flexibility needs, and operating pressure. For a broader comparison of adhesive strength and durability characteristics relevant to industrial sealing, see our review of which bonding method performs better for demanding, high-stress applications.
By carefully matching the sealing technology to your assembly’s specific requirements, you can build a seal that performs reliably over its full service life — and revisiting that match whenever an assembly is redesigned or its operating conditions shift keeps the sealing strategy current rather than inherited from a decision made under different circumstances. Contact Our Team to discuss the right sealing solution for your project.
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