Apply flux over newly soldered joint.

[Bob from accounting]

I watched a plumber apply flux to a freshly soldered joint. He had soldered a 1 1/4" ball valve, he went back around the entire joint and applied a healthy amount of flux all around the freshly soldered joint with the torch fully on, so an outer layer of flux coated over the new hot joint.
So he cleaned, fluxed, torched, applied solder, than went back and torched it back up and applied like a finishing coat of flux over everything with the heat on and this second coat of flux was brushed thoroughly over streaming hot joints?
Is this common to do after the fact?

 

[Terry]

We sometimes hit the joint with flux afterwards to both cool the joint and to get it a bit cleaner. Then the rag.
I use a fine mist of water to not cool it too quickly, and then the rag.

 

[Sponsor]

 

[Jadnashua]

Flux helps to keep the pieces from oxidizing from the high heat needed to melt the solder and helps the solder flow. I can't think of a good reason to add flux after the solder unless you saw that things didn't flow as well as you'd have liked. Then, it would only be useful if the existing flux hadn't been overheated and scorched. Terry came in just before me, so I guess there is a reason.

Years ago, they used an acid based flux, and you did need to clean the joint once you were finished. You cannot use an acid based flux these days on potable water systems, so you use a water based one. Water based ones are easier to overheat which can lead to a poor solder joint. They work fine if you're familiar with them and have good technique, though. It's still a good idea to clean the joint up when finished. The larger the pieces you're using, the longer you need to heat them to bring them up to temp to solder...suppose that could lead to heat migrating where you don't want it.

 

[Terry]

Wiping with flux afterwards can make things look cleaner. Not always though. It works both ways.

 

[Fitter30]

I do that then wipe the joint.

 

[Bob from accounting]

If you apply Flux afterwards and do not wipe it all up well, can this lead to issues down the road like corrosion or oxidation? Once I had a plumber tell me you always need to wipe off any flux and not leave any behind as it will be a problem, but I forgot why?
If you really wanted to impress with clean pipes, after it cools down can you hit it with fine steel wool, some polish and then a rag to make it shine like a pice of artwork?
It almost seemed like he was applying flux at the end thinking that it was going to fill in any gaps or help make a better seal?

 

[DIYorBust]

What is the advantage of this? Does it make a better joint? A better appearance? More corrosion resist?

 

[Terry]

What is the advantage of this? Does it make a better joint? A better appearance? More corrosion resist?

It's only for looks. It does not make the joint better.