Brush On Weld means: This is the weld it brushes on, as its name suggests. This is used to repair holes on cars that would otherwise be unroadworthy. It can be used as either seam sealer or underseal with brush on weld. It is easier than applying a metal weld because it does not actually join any metals together. Most spanner monkeys can apply it. (in Community Dictionary, added by Cason Macdonald)