Mastercool aluminum-filled metal repair epoxy — Alum Bond 90935, machinable high-strength paste (8,600 PSI, heat-resistant)

Mastercool 90935 Alum Bond is a high-strength, aluminum-filled epoxy paste engineered to permanently repair cracks, blow holes and porosity in aluminum castings, radiators, tanks and engine components.

Alum Bond combines a dense, aluminum-filled polymer matrix with a non-sag paste consistency and industrial-grade mechanical strength so technicians can repair metal parts on the bench or in the field. The compound cures to a machinable finish that can be drilled, tapped, sanded and milled, restoring function without the cost and downtime of replacement parts. It is formulated to withstand elevated operating temperatures and the stresses typical of automotive, HVAC and industrial environments.

How strong and heat-resistant is this repair compound?

The cured Alum Bond compound delivers industrial-level mechanical performance, with approximately 8,600 PSI compressive strength and 3,500 PSI tensile strength, providing a durable structural repair for many aluminum components. It also tolerates working temperatures up to 250°F (121°C) after full cure, making it suitable for many engine and HVAC applications.

• Compressive strength ~8,600 PSI for load-bearing repairs
• Tensile strength ~3,500 PSI for crack resistance
• Heat resistance up to 250°F (121°C) after full cure
• Engineered for automotive, HVAC and industrial conditions

Can I shape or machine the repair after it cures?

Yes — once Alum Bond reaches full cure it becomes a machinable metal-like material that accepts drills, taps, files and sandpaper. This lets technicians re-establish threads, restore sealing surfaces or blend the repair into surrounding metal without replacing the entire component.

• Drill, tap and machine with standard metalworking tools
• Sands and files to smooth edges and mating surfaces
• Holds threads when retapped into repair areas
• Enables functional restoration rather than patch fixes

How easy is it to apply, and will it stay in place on vertical surfaces?

Alum Bond is formulated as a non-sag paste, so it adheres to vertical, overhead and irregular surfaces without running. The controlled working time gives you enough time to force the compound into cavities, fill blow holes and shape the repair before it begins to set, while remaining tacky enough to tool for precise finishes.

• Thick paste consistency for gap filling and vertical repairs
• Controlled open time for accurate placement and tooling
• Good adhesion to clean, prepared aluminum and ferrous metals
• Ideal for filling porosity, blow holes and casting defects

What specific parts and defects is this product designed to fix?

This compound targets cast metal defects, sealing cracks, filling porosity and repairing blow holes on a wide range of aluminum parts used in vehicles and equipment. Typical applications include radiators, engine blocks, housings, tanks, valves and HVAC components where replacing the part is costly or impractical.

• Radiator and cooling system repairs — seal leaks and pinholes
• Engine block and housing patching for non-critical areas
• Tanks, pumps and valves — restore sealing surfaces and ports
• Castings with porosity or surface imperfections

Who is this for: Mastercool 90935 Alum Bond is aimed at professional technicians, maintenance crews and skilled DIYers who need a reliable, machinable metal repair that restores part function and avoids the expense and downtime of replacement. It is especially useful for automotive and HVAC service shops, industrial maintenance teams, restorers working on classic equipment, and any user who requires a high-strength, temperature-resistant aluminum repair solution.