Two sealing chemistries handle most industrial leak-prevention work: room temperature vulcanizing (RTV) silicones and anaerobic sealants. They cure by different mechanisms and suit different joints, and choosing the wrong one is a common cause of persistent leaks.
How Each Sealant Cures
Anaerobic Sealants
Anaerobic sealants are single-component liquids that stay fluid while exposed to air. They cure only when confined between close-fitting metal surfaces, starved of oxygen, and in contact with active metal ions such as iron or copper. The result is a rigid thermoset plastic that fills microscopic surface imperfections and creates full surface-to-surface contact.
Key characteristics:
- Cures in the absence of air, in contact with metal.
- Designed for small, close-fitting gaps, typically up to 0.5 mm.
- Primarily a metal-to-metal technology.
- Cures rigid and adds shear strength to the joint.
- Strong resistance to oils, fuels, and coolants.
- Heat resistance generally 150 to 200 degrees C for standard grades.
- Disassembly can require localized heat.
RTV Silicone Sealants
RTV silicones cure by reacting with atmospheric moisture at room temperature, releasing a byproduct such as acetic acid or alcohol, and forming a flexible elastomer.
Key characteristics:
- Cures on exposure to humidity.
- Fills larger, uneven gaps, often 6 mm or more.
- Adheres to metals, many plastics, glass, ceramics, and painted surfaces.
- Cures to a flexible, rubber-like film.
- High flexibility suits thermal movement, vibration, and dynamic joints.
- Some formulations withstand over 300 degrees C.
- Generally easier to peel or scrape away during service.
Cure Byproducts and Corrosion
RTV silicone chemistry matters when electronics or sensitive metals are nearby. Acetoxy-cure grades release acetic acid, which can corrode copper, brass, and some coatings and irritate operators in enclosed areas. Neutral-cure grades, using oxime or alkoxy chemistry, release milder byproducts and are the safer choice around electrical contacts, bare copper, and enclosed housings. Anaerobic sealants release no atmospheric byproduct, since they cure only in the confined joint, but the rigid cured film means a joint sealed this way is harder to open later.
Dispensing and Application
Anaerobic sealants are applied as a continuous bead to one clean, dry flange face, encircling all bolt holes, then assembled promptly so the joint closes before the surface film can begin to set. RTV silicones are applied as a bead sized to the gap, with parts brought together within the skin-over time, typically a few minutes. Both benefit from automated dispensing on higher-volume lines for consistent bead placement and volume, which reduces both squeeze-out waste and thin spots that leak.
A Direct Comparison
| Feature | Anaerobic Sealants | RTV Silicone Sealants |
|---|---|---|
| Curing trigger | Absence of air plus metal contact | Atmospheric moisture |
| Best gap range | Small, precise, machined flanges | Large or irregular, stamped sheet metal |
| Material compatibility | Primarily metal-to-metal | Wide range of materials |
| Cured state | Rigid thermoset plastic | Flexible elastomer |
| Structural contribution | Adds rigidity and shear strength | Provides flexibility and vibration damping |
| High-temperature limit | Good, 150 to 200 degrees C typical | Excellent, often over 250 degrees C |
| Disassembly | Can require heat | Generally easier |
When to Choose Which
Choose an anaerobic sealant when you have rigid, machined metal flanges with tight gaps, need to add structural integrity or resist movement, face high pressure or vibration, or expect exposure to aggressive fluids. A typical case is sealing the mating faces of a precision-machined pump housing.
Choose an RTV silicone when gaps are larger or irregular, the joint involves dissimilar materials such as metal to plastic, the assembly sees significant thermal expansion or vibration, high-temperature resistance is the priority, or future disassembly is expected. A typical case is a formed-in-place gasket on a stamped steel cover.
Matching the sealant to the joint geometry and service conditions prevents most field leaks. Email Us to review your flange design and operating envelope with Incure’s technical team.
How Incure Supports Sealing Projects
Incure helps you navigate RTV and anaerobic formulations based on joint design, material compatibility, temperature, pressure, and disassembly needs, and provides guidance on surface preparation, application technique, and cure conditions. Consider a manufacturer running cast aluminum housings with variable tolerances: a rigid sealant struggled with the inconsistent gap, while a high-temperature RTV accommodated the wider clearance and vibration. In contrast, a precision metal-to-metal engine joint benefits from a high-strength anaerobic sealant that also raises torsional rigidity.
For related selection guidance, see our comparisons of adhesive strength for heavy-duty repairs and cure speed for quick repairs, plus how thermal expansion mismatch drives joint failure.
Universal Best Practices
Regardless of chemistry, keep surfaces clean and dry, follow the technical data sheet for cure times and temperatures, and design the joint for adequate flange rigidity or gap. Remove all old sealant and gasket residue before resealing, since a partial layer of cured material prevents the new bead from seating. Allow the specified full cure before pressure testing; an early leak test on a partly cured seal can disturb the bond and produce a false failure. Where possible, validate the chosen sealant on representative hardware under actual operating temperature, pressure, and vibration before committing it to production.
Contact Our Team to identify the sealing solution that fits your assembly and process.
Visit www.incurelab.com for more information.