When a furnace shell cracks or an exhaust joint blows out, ordinary body filler chars and falls away within minutes. High-temperature putty is built for exactly this gap: a moldable compound that cures into a rigid, heat-stable solid capable of holding a seal where organic fillers cannot survive.

What Makes a Putty “High-Temperature”

Standard epoxy and polyester fillers rely on organic resin backbones that soften near 120 C and decompose well below 300 C. High-temperature putties replace or heavily load that backbone with inorganic material: silicate binders, ceramic powders, metal oxides, and reinforcing fibers. The cured mass behaves more like a fired ceramic than a plastic, so it keeps compressive strength and dimensional stability through repeated heating and cooling.

Practical service ratings span a wide band. General cast-iron and steel repair grades hold to roughly 1,000 C (about 1,800 F). Specialized formulations for kiln furniture, molten-metal handling, and furnace doors are rated beyond 1,200 C. Flange and joint sealants trade peak temperature for flexibility, typically topping out near 500 C but tolerating pressure and vibration better.

Core Advantages

• Heat resistance without a flame source. The putty is applied cold and cures at room temperature or with a modest bake, then withstands service heat far above its cure temperature.
• Gap filling and shaping. A stiff, non-slumping paste bridges cracks, rebuilds worn edges, and fills voids on vertical and overhead surfaces.
• Permanent set. Once cured, the repair does not re-melt, so a single application lasts through many thermal cycles.
• Chemical and oxidation resistance. Inorganic binders shrug off combustion gases, mild acids, oils, and the oxidizing atmosphere inside furnaces and exhaust systems.
• Electrical insulation. Many ceramic-filled grades are dielectric, which lets them anchor and insulate heating elements and terminals.

Where High-Temperature Putty Is Used

• Furnace and kiln maintenance: sealing cracked refractory, rebedding elements, patching door seals, and filling gaps around thermocouple entries.
• Exhaust and flue repair: closing pinholes and cracks in manifolds, downpipes, and stacks where welding access is poor or the base metal is too thin to weld.
• Boiler and pressure equipment: sealing minor leaks around access doors, handholes, and flanged joints on the fire side.
• Metal casting operations: repairing cast-iron and cast-aluminum tooling defects before machining or coating, and patching launders and ladle covers.
• Industrial ovens and dryers: rebuilding worn hearth sections and sealing panel joints against heat loss.
• Power generation: patching turbine casing insulation covers, ducting, and heat-shield hardware.

For components that need a continuous protective layer rather than a localized patch, a sprayable or brushable ceramic system may fit better. Our guide to high emissive ceramic coatings by substrate and service temperature covers that alternative.

Email Us with your substrate and peak operating temperature for a putty recommendation.

Incure’s Epo-Weld High-Temperature Putties

Incure produces a range of Epo-Weld high-temperature repair putties for demanding heat environments. Grades are available for cast iron and steel repair up to roughly 1,000 C, thixotropic pastes formulated for boiler doors and molten-metal contact at still higher temperatures, water-based aluminum repair compounds for cast-aluminum parts, and flexible organic flange sealants that hold pressurized joints at moderate heat. Package sizes run from small tubes for spot repairs to gallon units for production maintenance. Because each grade is tuned to a specific substrate and temperature window, matching the grade to the job is the key selection step.

Selecting the Right Grade

Confirm peak temperature, then add margin. Identify the highest temperature the repair will actually see, including transient spikes, and choose a putty rated comfortably above it. Running a putty at its ceiling shortens service life.

Match the substrate. Thermal expansion differences between the putty and the base metal drive cracking on every heat cycle. Cast-iron grades are formulated to expand and contract with iron; using an aluminum-repair grade on steel, or the reverse, invites early failure. Our explanation of how CTE mismatch causes bond failure applies directly to putty repairs.

Decide between rigid and flexible. Rigid ceramic grades give the highest temperature and abrasion resistance but tolerate almost no joint movement. Flexible flange sealants accept vibration and thermal breathing at the cost of peak temperature.

Plan the cure. Some grades air-cure over 24 hours; others need a staged bake, often a slow ramp to drive off water before full heat. Rushing the ramp traps steam and blisters the repair.

Application Guidelines

1. Clean aggressively. Grind or wire-brush to bright metal, then remove oil and soot with solvent. Inorganic putties bond mechanically to a rough, clean surface and poorly to scale or grease.
2. Undercut the crack. Vee out cracks and feather the edges so the putty has depth to key into rather than a thin skim that spalls off.
3. Work in layers on thick fills. Deep single applications shrink and crack; build up in passes within the recoat window.
4. Follow the cure ramp. Air-set first if specified, then heat slowly on the first fire to complete the ceramic set.
5. Inspect after the first cycle. Hairline shrinkage checks are normal; through-cracks or lifting mean a grade or surface-prep mismatch that should be corrected before returning the equipment to service.

High-temperature putty will not replace a structural weld, but for sealing, rebuilding, and insulating in heat that destroys conventional fillers, it is often the quickest reliable repair available. Where the load is structural, compare options in our review of which adhesive is stronger for heavy-duty repairs.

Contact Our Team for a repair-putty recommendation matched to your equipment.

Visit www.incurelab.com for more information.