Does J-B Weld Work On Cast Iron?

J-B Weld is used to join cracked or broken pieces of cast iron. The method was invented by a track mechanic as an alternative to torch welding. J-B Weld is a type of epoxy putties that glue the pieces of cast iron together.

Before the application of J-B Weld, the broken pieces or cracked parts should be well cleaned to avoid any impurities that may interfere with the strength of the weld. But the question remains: does J-B Weld work on cast iron?

What is cast iron?

Cast iron is a compound made up of carbon (2% to 5%), iron, and silicon. Other traces of elements that may be found in cast iron include phosphorus, manganese, and sulfur. Cast iron is utilized in the manufacturing industries to come up with products such as; engine parts, pipes, utensils, rims, and generators casing.

Regarding the composition and metallurgical structure, cast iron is sub-divided into six groups. These groups are: alloy cast iron, white cast iron, grey cast iron, ductile cast iron, malleable cast iron, and compacted graphite iron.

Despite its wide applications, cast iron is brittle, non-malleable, and cannot be twisted. To avoid the need of dumping away cracked cast iron, engineers around the globe have innovated various methods of joining them. The methods include welding using consumable electrical rods, brazing, cold metal stitching epoxy putties which are J-B Weld and Quick steel.

How effective is JB Weld on cast iron?

 There are various types of JB Weld as dictated by materials and operational standards. Cast iron absorbs and distributes heat uniformly and it is the major reason behind its application in manufacturing various products such as engine blocks. The material gains heat and cools efficiently without weakening and cracking. Operations temperatures and conditions should be considered while choosing the type of JB Weld to be utilized.

 Since cast iron is brittle, J-B Weld has been invented to join pieces of the cast iron together.

J-B Weld is a cold weld that provides strong and durable repair to join pieces of cast iron together.  The tensile strength of the weld is 5020 PSI and can withstand a temperature of 5500 Fahrenheit. The shearing strength of the J-B weld is 900 PSI at a temperature of 4500 Fahrenheit. From the manufacturer standards, below is the data regarding J-B weld strength.

PropertiesTest MethodResult
color Dark Grey
Working time (70° F) 45 min. max
Set time 4-6 hours
Cure time 16-24 hours
Maximum temperature (intermittent) 600° F
Maximum temperature (continuous) 500° F
Tensile strengthASTM Cl 6383960 psi
Adhesion strengthASTM D2973960 psi
Flexural strengthASTM D7903960 psi
Compressive strengthASTM 06953960 psi
Shore D hardnessASTM 0224085 (1wk)
ShrinkageASTM 017790.0%
Flash Power (uncured) 7400

What glue works best on cast iron?

J-B Weld is a type of epoxy putty that bonds cast iron materials together. It is a chemical compound that is reliable and easy to use. J-B Weld is made up of two parts which when mixed and applied to the desired area, the required outcome is achieved.

Other types of epoxy putties available include wood and concrete. Each of the epoxy putties is applied according to the properties of the materials. J-B Weld is designed to be applied on cast iron.

Which JB Weld is most effective for cast iron?

J-B Weld is meant to join cracked and broken pieces of cast iron together. The right J-B Weld product should be chosen to achieve the right quality and durability. Regarding cast iron, two types of J-B Weld that can be utilized are: J-B Weld SteelStik and J-B Weld High Heat epoxy putties.

J-B Weld SteelStik is hand mixable and non-rusty epoxy putty that is used to bond cast iron pieces and cracks. Upon mixing, the compound can be molded and shaped to fit the designated area. The compound sets in 3 to 5 minutes and after 1 hour, can be machined and painted. J-B Weld SteelStik has a rated tensile strength of 900 PSI and can withstand a temperature of 3000 Fahrenheit.

J-B Weld High Heat is hand mixable epoxy putty that is applied to cast irons which are used in high-temperature regions. This epoxy putty sets in 1 hour and after 8 hours, it can be machined and painted. Its resultant bond is tough with a tensile strength of 800PSI. J-B Weld High Heat can withstand continuous heat exposure of 4000 Fahrenheit and intermittent heat exposure of 5500 Fahrenheit.

Related: JB Weld vs Epoxy: Is There Really A Difference?

How do you apply JB Weld on cast iron?

When applying J-B Weld on cast iron, guidelines and procedures should be followed to get the desired outcome. The following are the best-designed procedure to be followed when applying J-B Weld on cast iron.

  1. Clean the intended surface using sandpaper to remove dirt, paints, and rust. Back and forth motion should be applied to do away with all the impurities.
  2. Using racks, water and soap, clean the surface and allow it to dry.
  3. Mix equal amounts of JB weld parts A and B until a uniform color is achieved. Manufacturers’ instructions should be followed at all times while mixing.
  4. The mixture is then spread on cracked cast iron surfaces and allowed to set as per the JB weld designed characteristics. The excess mixture should be scraped off using a putty knife before the mixture dries.
  5. After 8 hours for J-B Weld High Heat and 60 minutes for J-B Weld SteelStik, joined parts of cast iron can be machined and painted to enhance the durability of the JB weld.


J-B Weld has been proven to be one of the most efficient methods applicable when joining cracks and pieces of cast iron together. The appropriate J-B Weld product should be chosen so as not to compromise on durability and efficiency of the weld. Thus, considering the material properties and areas of application should be considered at all times.

J-B Weld High Heat and J-B Weld SteelStik are the best J-B Weld for cast iron. The outlined procedures and safety should be maintained during their application. Despite the efficiency of both J-B Weld, operation strengths and efficiency should not be exceeded.