I have had the best luck with 1/8 in. 5P rod. Run about 110-115 DC Amps and use a whipping motion. You will see the puddle flow together with the base metal very well. It is very hard if not impossible to produce a good looking weld with 5p, but it makes a high strength weld on rusty metal.
Some reasons continuous welds are not used
1. Heat Affection
2. Time
3. Locations
Some times too much heat is just as bad as too little. Additional renforcing may be a better alternative that welding continous
