HIGHHEAT EPOXY PUTTY - 2 OZ

J-B Weld's product page rates HighHeat to 450°F continuous and 500°F intermittent, with 4000 PSI tensile strength. (J-B Weld's general FAQ page lists 650°F for HighHeat putty sticks; we quote the lower product-page figure, since designing to it is the safe choice.) That covers intake manifolds, engine blocks, cast iron heating radiators and similar parts. It is still an epoxy repair, not a substitute for welding a cracked casting.

Not on the hot side. Exhaust manifolds and headers routinely exceed HighHeat's published rating, and above it the epoxy will smoke, give off odor and flake rather than hold. For exhaust leaks, J-B Weld makes purpose-built products: ExtremeHeat (37901, 1000°F), ExhaustWeld wrap (38572, 1100°F), Tiger Patch (600°F) for mufflers and tailpipes, and Ultimate Copper RTV (32325, 700°F intermittent) for flange joints. HighHeat suits the intake side, not the exhaust side.

No. HighHeat cures at room temperature, setting in about one hour and reaching full cure in eight hours. It does not need to be baked or run hot to harden. Cold slows it considerably, so apply above freezing and keep a space heater or work lamp near the repair if the area is cold. A hair dryer can help, but cure time is not guaranteed in low temperatures.

It was almost certainly not mixed thoroughly. Cut a full disc through both the outer layer and the inner core, then knead it by hand for a full minute until the color is completely uniform with no streaks. If it is still pliable well past the eight-hour cure window, remove it and start over with fresh material. Cold working temperatures also stretch cure time.

J-B Weld does not recommend it. HighHeat is non-toxic once fully cured but is not rated food safe, so it should not be used where it can contact food, even indirectly. On ceramic grills and BBQ lids it will also smoke and give off odor at cooking temperatures. For a broken grill part, welding, riveting or replacement is the better route.

Yes. After the full eight-hour cure, HighHeat can be drilled, tapped, machined, ground, filed and painted, and it cures dark gray. It will not accept powder coating or chrome plating, since it is not conductive and powder coat bake temperatures sit close to its limit. On outdoor repairs such as a clay chiminea, paint over the cured putty to add water resistance.