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Piedmont 10-24-2008 01:55 PM

When soldering copper, what causes the solder not to "suck in"?
I've replaced all the copper pipes in my house (in my area copper pipe only lasts 40 years), replacing it with new rigid copper pipe. Everytime I heated up a joint and applied the solder it would get "sucked in". I just did one that didn't suck in the solder which surprised me, the solder just seemed to melt around the fitting and stayed at the surface. What causes that?

My technique is:
Sand the fitting & the pipe
flux both
Slide them into each other and give a slight twist
Heat the middle of the fitting as, solder flows to the heat
Keep the flame applied until the flame turns green on the opposite side
Apply solder, and it "sucks" right in.
If it's 1/2" pipe apply 1/2" of solder. If it's 1" pipe I usually apply 1" solder

After doing all the steps above like I usually do, the solder in this case melted and flow around the outside of the fitting but didn't suck in. Now, it does appear to have fully covered the junction (even though it didn't suck in) but what causes that, and do you think my joint is junk?

DangerMouse 10-24-2008 02:00 PM

i'd start by pulling the joint apart to be sure no water had seeped into the joint. that would cause what you describe.


Piedmont 10-24-2008 02:06 PM

Hmm... this is new pipe & new fittings, to a new loop I haven't connected yet to water, and I've kept the pipe in the room with my wood stove (without a steamer) so, it should be very dry. Is there anything else besides water that causes that?

ScottR 10-24-2008 02:07 PM


If no water, then maybe something else got on it after you sanded, oil or somesuch? Maybe in that one case, the pipe and fitting didn't get hot enough..

Sounds like you're doing things right, though.

My 2c is that if you're ever unsure of a joint, pull it apart and redo it. Even it it turned out to be good, it's better to take the 5 min now than forever wondering when it will leak.

DangerMouse 10-24-2008 02:09 PM

hmmmm..... open a valve in the line to let air in? maybe pressure is doing it?


RippySkippy 10-24-2008 02:18 PM

I'd pull it apart and re-do it. DM may have something if it's a closed loop the increasing air pressure could force the solder out. Short of that it sounds like you have good technique. I guess I've never watched the flame on "the other" side...but be careful that you don't over heat the copper.

DangerMouse 10-24-2008 02:25 PM

agreed, it sounds like you're doing it all by the book..... hey rippy


Ultrarunner2017 10-24-2008 03:29 PM

If nothing else works, I would use a different fitting and / or piece of pipe. Maybe some invisible defect in the pipe or the fitting interacting with the solder.

skymaster 10-24-2008 05:21 PM

-.-. --.- -.. ..-.

DangerMouse 10-24-2008 05:30 PM

cqdf? huh?


Mike2756 10-25-2008 08:59 AM

Try all the steps you took but be sure the inside of the female fitting is brushed or sanded and apply the flux immediately after sanding to exclude oxygen. Be sure there is no pressure, or water getting into the pipe. If there is water getting into the pipe stuff a piece of white bread into the source side. This will obsorbe water for a little while and is harmlessly flushed away upon use. I always continue to apply solder after heat is removed and look for no gaps between the components. good luck

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