Need advice here. I’m new to sweating copper pipe, but know that water will make any sweat fail. When doing some joints I was careful to make sure the flux had “boiled” out of the joint before hitting with solder. When done the joint was black, and I suspect I over heated and don’t have a solid joint. No leaks, but ...

I treated the flux like water, when I think I should have not worried about the boiling flux and just hit the joint with solder when the solder melted.

Is this best a redo before I close up the wall, or just go forward since the joints are working now?

Any comments or advice is appreciated.

 

The appearance of the outside of the pipe is cosmetic. If the joint holds water pressure that is what matters. Where people often fail is they don't clean the copper sufficiently inside and out, and the tarnish can make the joint fail.

But yes, you want to sweat it as soon as it's hot enough and before you've cooked off all the flux or turned it black inside the fittings.

 

There is only a short time between after the pipe is hot enough to melt the solder and before the flux is cooked off and the copper re-tarnishes.Do not poke the solder into the burner flame.

It takes practice and remembering for each pipe size how much flux to put on and what angle you aim the flame at the pipe to get it right.

Sometimes it is really better to take away the flame before all of the needed solder has been applied and soaked into the joint but it takes more practice to figure out how soon to take away the flame.

 

And to clarify.

As XS stated, clean, clean, clean, clean!

Throw away that old flux, dont use old acid brushes, use clean emery cloth, dont touch clean surfaces.

I like MAP gas, much hotter just takes seconds to heat.

And, you apply heat to the fitting, not the pipe!

 

Also remember to keep moving the flame. You don't want to "cook" the flux from a spot that got too hot. That's a sure fire recipe for a leak.