J-B Weld RTV Silicone Gasket Maker — Ultimate Black 9.5 oz, High-Temp Flexible Sealant

J-B Weld 32929 Ultimate Black is a high-temperature RTV silicone gasket maker and sealant that cures to a flexible, waterproof gasket for engine and mechanical applications up to 550°F continuous (650°F intermittent).

Designed for demanding automotive and mechanical environments, this 9.5 oz tube of black RTV silicone forms a long-lasting, non-shrinking seal when exposed to atmospheric moisture. It bonds to most metal, painted surfaces, and many plastics, giving professionals and DIYers a reliable option for replacing cut gaskets, sealing covers, and stopping leaks where heat and oil resistance are required.

How does J-B Weld Ultimate Black hold up under high temperatures?

The formula is engineered for continuous service up to 550°F and can tolerate short-term spikes to 650°F, making it suitable for many engine and exhaust-adjacent components. It remains flexible after curing, resisting cracking and breakdown under thermal cycling.

• Continuous temperature rating: up to 550°F
• Intermittent temperature spikes: up to 650°F
• Maintains flexibility to withstand expansion and contraction
• Formulated to resist weathering and oil exposure

What surfaces and parts can this gasket maker be used on?

Ultimate Black bonds to a wide variety of substrates commonly found in automotive and mechanical assemblies. Use it to form custom gaskets or repair existing seals on parts exposed to heat, oil, or moisture.

• Compatible with metal, painted metal, and many plastics
• Ideal for oil pans, valve covers, timing covers, differential covers
• Works on water pumps, drive housings, oven doors, and exhaust-adjacent areas
• Sensor-safe formula for many engine applications

How do I apply and cure the RTV silicone for the best seal?

Application is straightforward: clean and dry mating surfaces, apply a continuous bead, and allow moisture in the air to cure the seal. Cure speed depends on bead thickness and ambient humidity—thin beads skin over faster while thicker seals require longer to fully set.

• Surface prep: remove old gasket material, oil, and debris for maximum adhesion
• Apply a consistent bead; hand-tighten parts to compress the gasket after application
• Initial skin forms quickly; full cure time varies with thickness and humidity
• Do not use as a permanent spacer; allow proper curing before exposing to fluids or high pressure

Is this product suitable for professional repair shops and DIY projects?

Yes—both professionals and home mechanics use J-B Weld Ultimate Black for dependable, long-lasting seals. The tube format and forgiving cure behavior make it accessible for one-off repairs and repeat use in busy shops.

• Used by builders, mechanics, and repair pros for durable gasketing
• Tube size (9.5 oz) balances capacity with ease of handling
• Sensor-safe and resistant to weathering for confidence in repairs
• Can replace pre-cut gaskets where custom fit is required

Who this is for: If you need a high-temperature, oil-resistant gasket maker for engines, housings, or appliances that see heat cycling, J-B Weld 32929 Ultimate Black is built for both professionals and informed DIYers. It’s a solid choice when a flexible, durable seal is required across a range of mechanical surfaces, and when sensor compatibility and resistance to shrinking and cracking are important considerations.