How to Weld Cast Iron Correctly

YouTube user Brandon Lund wanted to demonstrate cast iron welding tips, so he simulated a crack on a dirty exhaust manifold. Cast iron exhaust manifolds are sometimes difficult to weld due to cast iron’s brittle nature. Cast iron was developed as an alternative to wrought iron: cheaper but also inferior in tensile strength. Brandon used Muggy Weld 77 and 72 electrodes to weld his cast iron manifold. Muggy Weld cast iron electrodes do not require special pre-heating or cool down and this enables the user to make repairs without disassembling the cast iron part.

To properly weld cast iron, thorough preparation is essential, and Brandon began by carefully cleaning the damaged area. Using a grinder, he removed all paint, rust, grease, and surface contaminants, exposing clean, bare metal along the entire length of the crack. This step is critical when you weld cast iron because the material is highly sensitive to impurities. Even small amounts of contamination can introduce porosity, weaken the weld, and increase the risk of cracking during cooling. Clean metal ensures better fusion and a more reliable repair.

After the surface was cleaned, Brandon addressed the structural integrity of the crack itself. He used a hand drill with a 3/16-inch drill bit to drill a hole at each end of the crack, a technique commonly referred to as stop drilling. When working to weld cast iron, stop drilling is especially important because cast iron is brittle and prone to crack propagation. These drilled holes help relieve stress at the crack tips, effectively containing the damage and preventing the crack from spreading further during the welding process or as the metal cools. This step greatly improves the longevity of the finished repair.

With the crack fully contained, Brandon moved on to the final preparation stage. Using a disc grinder, he beveled the cast iron along the length of the crack to form a clean v-groove. Creating this bevel is a key step when you weld cast iron because it allows for proper weld penetration and ensures the filler metal can fully bond with the base metal. The v-groove also provides space for controlled weld buildup, reducing internal stress and resulting in a stronger, more durable repair that is far less likely to fail over time.

Note: Brandon also demonstrated “the spark test” to help viewers identify whether a metal is steel or cast iron before welding.

Brandon used a Blue Demon 160 welder set at 60 amps, and 3/32” diameter rods.

This cast iron exhaust manifold was heat affected (burnt), so Brandon began the weld with the 72 rod then followed with the 77 rod. He laid deposits of only 1 inch at a time. After the first weld pass Brandon lowered the amperage to 50 to eliminate undercutting. This created a smoother deposit.

Muggy Weld 72 electrode is specially formulated to seal contaminates which may cause porosity. This allows the electrode to anchor deep into dirty cast iron. Once the 72 electrode was anchored in, Brandon completed the exhaust manifold repair with 77 electrode. 77 filled the cast iron and allowed for expansion and contraction of the parent metal post weld. The end result was a crack-resistant weld that required no special pre-heating or cooling. This repair only a few inches of electrode.

Thank you, Brandon for allowing Muggy Weld to feature your video on our site. Please subscribe to Brandon’s channel using the following link:

Brandon Lund Builds

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Updated 1/26/26