Gasket Sealants

Gasket sealants cure between two flange faces to form a leak-tight seal — either replacing a cut gasket entirely as a form-in-place gasket, or backing one up to fill machining marks and surface imperfections. AIMS Industrial stocks the Loctite range in depth — RTV silicone gasket makers, anaerobic flange sealants and flexible gasket eliminators — alongside Sanvo, Ultraloc (Molytec) and OSI options for general-purpose and construction-grade sealing jobs. Whether you're resealing a gearbox housing, sealing a compressor flange or replacing a timing cover gasket, the right chemistry and cure type matters more than the tube it comes in. For more on selection, see our RTV Silicone Gasket Maker Guide: Application, Cure Time and Selecting the Right Product.

Quick Reference — Gasket Sealant Types

The two core chemistries do different jobs. RTV silicone cures on exposure to atmospheric moisture and stays flexible, so it suits joints with some movement or gap. Anaerobic sealant cures in the absence of air between close-fitting machined metal faces, giving a thinner, harder, more rigid bond. Match the product to the joint, not just the brand.

Always confirm the exact temperature and gap-fill rating on the product datasheet before committing to a critical joint — grades within the same family can differ.

RTV Silicone vs Anaerobic vs Gasket Eliminator — What's the Difference?

RTV silicone gasket makers

RTV — room-temperature vulcanising — silicone cures by reacting with moisture in the air. It stays flexible once cured, conforms to surface irregularities, and can be cut through cleanly at disassembly, which is why it's the default choice for joints you'll need to service again. Loctite's RTV silicone range spans a general-purpose black (598), a drivetrain-focused grey formulated for extra oil resistance and bonding to both metal and plastic (SI 5699), a blue oxime-cure grade rated for plant maintenance and OEM use (587 / SI 587), a copper-coloured grade aimed at corrosion-sensitive, high-heat spots like sensor housings (5920 Copper Maxx), a heavy-bodied flange sealant that can withstand an in-line low-pressure test before it fully cures (SI 5900), and the high-temperature red grade rated to +316°C for exhaust, furnace and boiler work (596 Superflex).

Anaerobic flange sealants and gasket eliminators

Anaerobic sealants do the opposite — they cure in the absence of air, between two closely fitting metal surfaces, and won't cure properly across a large gap or on non-metallic substrates. The payoff is a thinner, more rigid, chemical-resistant bond ideal for rigid metal-to-metal flanges that don't flex in service. Loctite 510 fixtures in around 25 minutes and is rated to +200°C with strong resistance to fuels, oils and hydraulic fluid — well suited to transmissions and high-heat powertrain assemblies. Loctite 518 is the rigid gasket-eliminator grade for machined flanges, filling gaps to 0.25 mm across a -55°C to +150°C service range. Loctite 5127 is the flexible anaerobic option, formulated to flex with the flange rather than crack when vibration or thermal cycling moves the joint.

Which one replaces a cut gasket?

On many flat-flange joints — engine covers, gearbox housings, pump casings — a form-in-place gasket sealant works without a cut gasket at all, and modern RTV and anaerobic formulations often seal a resurfaced or slightly imperfect face better than a cut gasket would. Where the OEM specifies a gasket of a defined thickness for a crush dimension or shim purpose, stick with that gasket. Don't substitute sealant on a critical structural or high-pressure joint without checking the manufacturer's guidance first.

Choosing the Right Gasket Sealant for the Job

• Joint will be serviced again: use an RTV silicone. It stays flexible after cure and cuts through cleanly at disassembly, unlike a rigid anaerobic bond.
• Rigid, close-fitting metal flange under load: use an anaerobic gasket eliminator (510, 518 or 5127). They fill machining marks and give a uniform, chemical-resistant seal across the whole flange face — but need degreased, closely mating metal surfaces to cure properly.
• High-temperature exhaust, furnace or boiler work: step up to a high-temperature RTV grade like 596, rated to +316°C, rather than a general-purpose silicone rated for standard engine temperatures.
• Corrosion-sensitive components (sensors, aluminium housings): Loctite 5920 Copper Maxx is formulated for exactly this — high-temperature resistance without migrating once applied.
• Budget-driven general workshop use: Sanvo, Ultraloc and OSI RTV silicones cover routine engine, equipment and construction sealing at a lower price point than the full Loctite range.

Application Best Practice

Clean both mating faces with a residue-free cleaner such as brake cleaner rather than a general solvent — many solvents leave a thin film behind as they evaporate, which interferes with the sealant's ability to bond and cure against the metal surface. Apply a continuous, unbroken bead around the bolt pattern and sealing perimeter; gaps in the bead are the most common cause of a leak that shows up after assembly. Respect the stated tack-free or fixture time before handling the joint, and the full cure time before pressurising the system or returning the assembly to service — these vary by product, so check the datasheet for the specific grade you're using rather than assuming. For anaerobic sealants specifically, keep the mating faces close and metal-to-metal; a large gap or a non-metallic surface will stop the product curing properly.

Companion Ranges

Gasket sealants are one part of a broader sealing and fastening job. See our gaskets range for pre-cut options where the OEM specifies a fixed thickness, sealants for our full sealant category, and pipe sealants for thread and pipe-joint sealing rather than flange gasketing. If the job also needs a fastener secured or a bearing retained, our threadlockers and retaining compounds ranges cover those separately — different chemistry, different job. Browse the full Loctite range for the complete adhesive, sealant and threadlocking line-up from the one brand.

Order from AIMS

Need help picking the right grade for your flange, temperature and fluid exposure? Call our team on (02) 9773 0122, get in touch via our contact us page, or request a quote for volume or trade pricing. We're a proudly Australian-owned industrial supplies business, and we're happy to talk through the right product for your application before you order.

People Also Ask

What's the difference between RTV silicone and anaerobic gasket sealant?

RTV silicone cures by reacting with moisture in the air and stays flexible once set, making it the right choice for joints you'll disassemble again. Anaerobic sealant cures in the absence of air between two closely fitting metal surfaces, giving a thinner, more rigid bond suited to flanges that won't flex in service. They're not interchangeable — pick by joint geometry and how tight the mating faces are.

Can gasket sealant replace a cut gasket entirely?

On many flat-flange joints — engine covers, gearbox housings, pump casings — yes, a form-in-place gasket sealant works without a cut gasket, and can seal a resurfaced or slightly imperfect face better than a cut gasket would. Where the manufacturer specifies a gasket of a set thickness for a crush dimension or shim function, use that gasket instead.

Which Loctite gasket sealant handles the highest temperature?

Loctite 596 Superflex, the high-temperature red RTV silicone, is rated to +316°C and is formulated for exhaust systems, furnaces and boilers. Standard RTV grades such as 598 or SI 5699 suit general engine and gearbox sealing rather than the highest-heat applications.

What's the difference between Loctite 510 and 518 anaerobic flange sealants?

Loctite 510 fixtures in around 25 minutes, is rated to +200°C, and carries strong resistance to fuels, oils and hydraulic fluid — suited to transmissions and high-heat powertrain assemblies. Loctite 518 is the rigid gasket-eliminator grade for closely machined flanges, with a 0.25 mm gap-fill across a -55°C to +150°C service range. Check both datasheets against your specific joint before choosing.

Do I need a different sealant for aluminium versus steel flanges?

Most anaerobic and RTV silicone gasket sealants are formulated to bond both aluminium and steel, but always check the specific product listing — some grades are tested and rated on unprimed aluminium and steel together, while others may need a primer on certain substrates. When in doubt, ask our team before you commit to a critical joint.

Why clean flange faces with brake cleaner rather than a general solvent?

Many general-purpose solvents leave a thin residue film behind as they evaporate, and that film can stop the sealant bonding and curing properly against the metal. Brake cleaner is formulated to evaporate without leaving a residue, giving a genuinely clean surface on both mating faces for the sealant to grip.

How long before I can put the assembly back into service?

Tack-free and fixture times vary by product — typically 15 to 30 minutes for RTV silicones and around 25 minutes for an anaerobic gasket eliminator like Loctite 510 — but full cure to service pressure takes longer again. Always check the specific product datasheet rather than assuming one cure schedule applies across the whole range.

Is a flexible or rigid gasket eliminator the right choice for my flange?

Use a flexible anaerobic gasket eliminator, such as Loctite 5127, on a flange that experiences vibration or thermal expansion and contraction in service. Use a rigid grade like Loctite 518 where the flange is closely machined and won't flex, and maximum pressure resistance matters more than movement tolerance.