Early vs. late failure of sweat solder joints

I just re-ran some of the 1/2 and 3/4" lines in our basement. After finishing, out of about 50 sweat solder joints that I did, 2 had small leaks that needed to be redone. System has been completely dry for the last 2 days now.
Question: - Do most leaks do to bad solder joints show up immediately or do they continue to show up over time?
Basically, since I did have a couple of bad solder joints I am concerned that maybe some others are marginal and will fail later (when I am not looking). Is that likely or does the initial pressurization (along with some shaking of the pipes that I did) pretty much show up the bad joints?
Thanks
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blueman wrote:

Hi, Need more practice, Eh? I hate to redo the job when it leaks. I prepare 110% when soldering, LOL! Quality is doing right first time. If soldering was marginal, when it is exposed to mechanical stress it can leak later but if it does not leak now just leave it be.
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Depending on how many of them were 3/4", 96% good is pretty decent.
I have never had one leak afterwards. But yes, I have worried about it just as you are now. Relax.
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I never had a leaker using the old 50/50 lead/tin solder. I did some work last year with the new lead-free solder and flux designed for it, and had a couple of leakers at the outset. HOWEVER, about 6 weeks after putting the plumbing into service I had one joint that sprung a bad leak. Don't know how it held up for 6 weeks before leaking, possibly the flux was burnt and left a path that the water pressure slowly worked it way through pushing the flux out until a clear path developed. I am normally meticulous in cleaning and coating with flux and soldering a filet around the edge of the fitting.

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Maybe that's my problem... I bought some new lead-free solder because I wasn't sure whether my old solder was or not (I bought it 10 years ago and the label had faded). However, I still used my old flux.
- Is there really a special flux for the new solder? - Is there a problem with using the "old" flux?
And, by the way, I too am meticulous in cleaning joints and using plenty of flux.
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Yes, lead free solder requires a different flux. Use the old stuff and it won't flow the same.
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After having problems soldering with lead free solder and the flux they sell to use with the lead free solder, I switched back to the old paste flux that I had used with lead based solder and had better, but not perfect, results.

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EXT wrote:

It also pays to get good quality solder. My buddy was trying to change his water heater and he called me because he was having trouble soldering. I tried to use the solder he bought from home depot and it just wouldn't wet. We stopped over a local supply house and bought a roll (for less than he paid at the big box) and it wet just like 50/50.
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Is the solder at Home Depot really that bad? They seem to sell the standard Oatey "Safe Flo Lead Free Plumbing Solder" that I have sen sold at a lot of other places. Is the stuff sold at supply houses really better?
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I did my house with the Home Depot stuff, switching from iron to copper. No problem other than getting burn in the face and hands from the dripping solder while working upside down under a tight crawl space.
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