Fusion Welding Auxiliary Paste

The paste is not a filler material, but an aid to clean the surface and improve wetting. It breaks up the oxide layer and reduces surface tension, so the weld metal flows better and the penetration is cleaner. If you leave it out, you risk porosity and lack of fusion, especially on tough material. Apply it thinly and evenly to the joint edges before striking the arc. It's important to use the product that matches the material, otherwise you can make the weld worse rather than better.