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Old 12-15-2012, 09:23 AM   #1
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Can you re-solder over new solder?


I am trying to install a hot water baseboard loop in an upper level and I have never done any soldering or copper plumbing before. On the whole, I think the joints are coming out well, but I have a little doubt about one or two. The loop isn't complete, so there has never been water in it. My question is can you re-heat the joints in question and simply add more solder to the top of the existing solder? I have 3/4" Type M copper pipe and heating elements (Slantfin 15). Thanks in advance.

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Old 12-15-2012, 09:30 AM   #2
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Can you re-solder over new solder?


I have been able to do it....but personally, I would pull that one apart and do it over. The most common cause of leaks is dirt in the joint and/or not enough heat.

What I do it heat it up so that it will pull apart....once it's apart, I wipe the male end with a damp rag which leaves only a real thin skim coat of solder....if you have any voids, it's real obvious. Apply some more flux...heat up and push the female fitting back on. You only need to apply a little solder at this point.

One important point about sweating pipes (besides being real clean)....one of the common mistakes is to apply the solder too soon....I keep touching the joint with the end of the solder until I see the solder melt real quick....if it beads....it's not hot enough...when it's hot enough to melt quick...then apply....the joint should 'suck' the solder up...when it's doing that, you know your getting a good joint.

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Old 12-15-2012, 09:34 AM   #3
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Can you re-solder over new solder?


You can do that. However if it didn't go right the first time then there could be dirt in it. Adding more solder will not fix it. You need to take it apart, clean it and do over. You do not need to clean all the old solder off just the dirty areas.
If you simply did not add enough solder the first time the reheat and add more as needed. You might need a bit of flux to make it flow.
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Old 12-15-2012, 09:37 AM   #4
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Can you re-solder over new solder?


Thanks Dave. My pipes are all brand new and I cleaned them really well to a bright penny look. I am using MAP gas, so I think that gets them hot enough pretty quickly. I do the same with the solder as you, touching it slightly until it melts, then I heat the joint a couple seconds more and apply the solder, bending the solder stem into a hook so I can do the bottom and back side of the joint first and then run it around the joint. I am thinking and hoping they are good, but am a bit paranoid, since I am new. Is there a way to air pressure test the joints before filling the system?
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Old 12-15-2012, 04:02 PM   #5
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Can you re-solder over new solder?


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Originally Posted by tpagel View Post
Thanks Dave. My pipes are all brand new and I cleaned them really well to a bright penny look. I am using MAP gas, so I think that gets them hot enough pretty quickly. I do the same with the solder as you, touching it slightly until it melts, then I heat the joint a couple seconds more and apply the solder, bending the solder stem into a hook so I can do the bottom and back side of the joint first and then run it around the joint. I am thinking and hoping they are good, but am a bit paranoid, since I am new. Is there a way to air pressure test the joints before filling the system?
Ayuh,... All it takes is fitting in a schrader valve, 'n a pressure gauge,...
Then add air,...

Run it up to 'bout 30 psi, 'n listen while yer waitin'...
If it leaks, it's usually obvious...

It can be at either end, or wherever you want,...
leave it in-place for future fun...
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Old 12-15-2012, 05:15 PM   #6
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Can you re-solder over new solder?


You did not mention flux. Are you using tinning flux? I mix tinning and regular, works great, Also hook solder. Heat on fitting only. Capillary action will suck the solder right in. A telltale little drip on the bottom says OK. Dont hit with wet rag. Can crack solder. wash later with dish detergent and warm water. NEVER HAD A LEAK.
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Old 12-15-2012, 08:26 PM   #7
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Can you re-solder over new solder?


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What I do it heat it up so that it will pull apart....once it's apart, I wipe the male end with a damp rag which leaves only a real thin skim coat of solder....if you have any voids, it's real obvious. Apply some more flux...heat up and push the female fitting back on. You only need to apply a little solder at this point..
If there are voids, chances are that by now those spots are oxidized from the first go-round heated up for soldering, and now those spots need re-sanding and then more flux.
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Old 12-16-2012, 08:28 AM   #8
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Can you re-solder over new solder?


Most people don't realize the solder on the outside does absolutely nothing, it's what's inside the fitting that counts. You have to have fill the void in the fitting with solder I never cared about the outside.
Oh Yeah a lot of guys will wipe it or clean it to make it look better but it's all the same. Never had a leak thousands of joints later, alright alright I had a few don't tell anybody.
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Old 12-17-2012, 12:31 AM   #9
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Can you re-solder over new solder?


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Oh Yeah a lot of guys will wipe it or clean it to make it look better but it's all the same.
Yeah, I didn't bother with that, but I did come back after the pipes were cool to wipe away the flux residue. I've heard it can cause corrosion later, if not removed.

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