Hercules Boiler Solder makes strong lasting repairs on leaks in steam boilers caused by leaking joints or sand holes during installation, or older installations where corrosion, vibration or settling causes leaks and cracks. This easy-to-use, non-metallic powder finds the trouble spots and forms a tough seal which expands and contracts with heat, resists high pressure, and temperature. Hercules Boiler Solder is for use on all hydronic systems including those with rubber or plastic components. This product remains in the boiler water of steam systems and will not seal leaks in the radiator circuit. Available in two variations of sizes: 1 lb and 200 lb.