Thread: silver solder flux residue

You don't need flux on a copper to copper join?

If it's for a brass fitting, when welding use the feather on the flame to burn off the ecxess.

Or leave it?

Wire brush if your really worried, copper to copper, unless its really filthy or being a mongrel to weld dont bother with flux.

Guys, Will the residue cause any problems if I don't clean it?

Originally Posted by emptybucketman

Guys, Will the residue cause any problems if I don't clean it?

Sorry bloke; just re-read and realised I didn't answer the question.

Short answer is No.

Long answer is - You may have noticed that the flux looks kind i=of "glassy", If the flux residue is inside the weld and you get movement in the pipe ( expansion or physical movement) the flux will crack ( like glass). That's why usually the flux is feathered away with the flame at the time of the weld. If it's not in the joint it won't matter.

As for flux that is on the outside surface of the pipe, it won't do anything but might flake off at some point, It won't make the pipe rust or burst or whatever.

I know this is a late response but it may be of interest to someone.

When I use flux such as for silver soldering brass or steel to copper I clean the completed joint with a long strip of rag which has been wet with hot water. I like to do this as it allows you to make a thorough inspection of the joint to ensure the solder has flowed completely around the circumference of the pipe and there is no pinholes. The job looks better and the removal of the flux reduces future corrosion of the steel component of the joint. The actual cleaning is done by wrapping the rag around the joint and see sawing backwards and forwards until the joint is clean and shining.

(I am a retired refrigeration mechanic)

You shouldn't cool copper joints with water unevenly, this practice may cause cracking in the solder joint,