Solder copper pipes under kitchen sink?


Is it common to solder copper pipes under a kitchen sink, or is it almost universal to use compression connections there? If you found some already soldered there, and wanted to put new connections in, would you use a torch to remove the old ones, then use compression connections for the new ones? Or what?
Especially if pipes come out of a concrete slab foundation, and only stick up 2 or 3 inches, so there is not much excess pipe length to cut and start over.
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Take it from an expert....you seem to be way over thinking this (like I sometimes do)
How does your exsiting plumbing terminate?
If your existing plumbing is soldered & terminates with a threaded fitting to which the angle stops are attached...just unscrew the old angle stops & install new ones.
You can plumb your under sink connects just about anyway you want.
Dual outlet angle stops are available to service kitchen sink, dishwasher & ice maker. Angle stops are hardly ever used so having the dishwasher share with the sink hot water isn't a huge deal.
I'm not a huge fan of compression fittings but they're quick & easy.
Not being able to see your installation makes it difficult to determine the best way to go. Some photos or a complete description fo the existing condition would help.
If your plumbing comes out of the slab, I would not cut any tube off. I'd use the existing fittings if I could get them to work. Failing that, I'd sweat off whatever I had to & then use compression fittings or Shark Bites.
cheers Bob
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It's very common to solder copper pipes under kitchen sinks to do plumbing up to the angle stops, re-route pipes, etc.
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Thanks for the answers. The pipes from the foundation are terminated with seemingly-soldered adaptors to provide compression threads. One chromed faucet pipe is stuck in one of those, with the compression nut unscrewed. The other chromed faucet pipe has been removed by me (easily) and replaced with a hose designed for connecting to the faucet, and is now leak-free. Except I still might want to connect other stuff to it.
The lower end of that faucet hose has compression hardware built-in, to connect directly to the compression threads mentioned above. Is that kind of hose-end connection reusable? Or does the first-time compression of it cause it to become significantly less reliable the 2nd time you compress it? In other words, can you unscrew it, put a valve or tee or something like that in between, then screw it back, and not expect it to leak?
As for the stuck pipe, if I cut it and bend it, can I "unscrew" it, causing it to become unstuck by lots of turning? Or is there a better way to remove it? It seems like it has something inside catching on the soldered compression adaptor. And I can't put a lot of force on it to remove it, because anything I use as a fulcrum to get leverage, just bends the floor of the under-sink cabinet.
I don't want to destroy the stuck pipe till I'm sure I know how to remove it, because, presently, even though it has a very minor leak, it's working, when I put the compression nut back on. And I have to turn off all the water in the house to work on it, because there is presently no stop valve there. So, if I cut it and bend it, to try to unscrew it, we're stuck with no water till I finish the job.
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I am confused. It is important to know that compression fittings use a different threading than threaded pipe fittings. Don't try to mix them or you will destroy both sets of threads. If you are talking about compression fittings that use a brass ring on the pipe, they usually cannot reliably be reused, often leaking. This is why I don't like to use compression fittings on standard copper pipe such as you have sticking out of the concrete because the only cure for the crushed copper is to cut it back, which you don't want to do. I would use only soldered fittings on the pipe with conversion fittings to adapt to the supply tube and/or valves that you should install.
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Right, for example a hose that connects a faucet to the water supply below uses a threaded pipe (NPT) fitting on the faucet and a compression fitting on the water supply. And that kind of compression fitting is different from the kind that goes on bare copper pipe. So that's three different kinds of fittings, two of which are compression.

What about the kind of compression fitting that doesn't use a brass ring (ferule?) but just compresses the fitting directly against the pipe, with an insert (of unclear purpose) in the pipe?

And I've never soldered pipe before. The only soldering I have done is electronic circuits, which is an entirely different kind of work. If I heat the adaptor with a torch, do I then just lift it off the pipe? With a tool such as pliers? How will I know when it's heated enough? Will the heat of the pipe heat the pliers and burn my hand?
The main reason I have to remove one of the present soldered adaptors is that the thin pipe to the faucet is stuck in that adapator, as if it had something connected to the lower end which wouldn't fit through the adaptor, and there is no easy way to apply enough force to remove it, because of the awkward position.
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OP-
imo you're not going to get sufficient help / info from this thread to successfully execute this repair.
I sweated more joints than I can remember and thinking back to when I was a rookie (a LONG time ago) .....I would be very reluctant to attack this situation as my first tube soldering experience.
If you don't want to hire a pro...do you have a friend, neighbor or relative who could help you through this?
Or you could hire a handyman..... not so much to do the job but to show you how.....nothing beats a demo.
Thirty years ago, despite being a pretty accomplished DIY'r, I hired a professional plumber because I was just too jammed up for time. To this day, I still use all the tricks he taught me. Probably the best $500 I ever spent on a home repair.
cheers Bob
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I'm having trouble following & understanding the description of the installation.
Any chance of some photos? Are there no angle stops? Sounds like a hack job.
cheers Bob
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On Aug 23, 1:37am, snipped-for-privacy@optonline.net wrote:

Yes, I agree with you, I do it all the time.
But from the OP's questions I'm getting the sense that he's not all that experienced and the best bet for him is to "keep it simple".
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Cut back to clean pipe. Put a sweat union on slab end and 4, 6, 12", etc. extension in the other end of the union. Now you have all the pipe you want to sweat or use compressions on with plenty of screwup room. If pipe gets to short in future, just heat union and replace extension. Slab pipe never gets shorter again.
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Don't know about common, but I hate compression fittings. Everytime I have to turn a valve attached to a compression fitting, I worry I would disturb the fitting and cause a leak.
I did put in solder fittings under a sink. Just had to make sure there are no plastic pipes nearby and put metal shield on anything that burns easily (wall or cabinet).

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I do sweat & compression depending on the situation. Never had one "get disturbed". I just check the box for each particular comp fitting for how much to tighten after contact. 1/2 turn is what I usually see if I recall and that's all I do. Not 1/2 plus a little more. With various comp type fittings, go by the book. If it drips a tad, then go another 1/6 turn. You can always tighten a tad but leaking because it's overtight means take off and redo. Good part about compression is no heat to be concerned about surroundings or mess up internals of valve.
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Anagram wrote:

If you solder under the sink, take great care to not burn anything; use a heatshield made of steel (not aluminum - melt), preferrably with some fiberglass or rock wool cloth behind it for thermal insulation. I've seen scorch marks on almost every job where pipes located near walls were soldered, and in one case they managed to melt all the low voltage wires running through metal conduit located 6" from a pipe.
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