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Thread: If solder won't melt, is the ONLY reason that the joint wasn't hot enough?

  1. #1
    DIY Junior Member Studly's Avatar
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    Default If solder won't melt, is the ONLY reason that the joint wasn't hot enough?

    I'm no pro, but have done a fair amount of sweating copper joints. I always clean the heck out of the fittings, apply Oatey #95 tinning flux to the joint, and then use a propane torch to heat the fitting (not the tubing). I heat up the fitting, and after the flux boils away, touch the solder to the opposite side of my torch periodically to see if it'll melt and keep doing it until it melts. This has worked fine in the past.

    Problem is, I've been trying to sweat fittings onto a shower valve and on about half of them (in this case I'm heating the valve part, not the thinner fittings), I couldn't get the solder to melt ... even after heating them for about 5-10 minutes with my propane torch, with about a 3 inch flame, touching the inner cone of the flame to the female part of the joint. In fact, the valve fitting was starting to become discolored and the flux melted, so it seemed like it was well heated.

    This valve wasn't connected to the water supply yet, so there wasn't any water in the fittings or valve. Is there any other reason why solder won't melt? This is a no-name brand of solder, but it worked fine in the past and worked fine and melted on half of the joints. My torch is getting low on propane, but the flame seemed fine. As I heat the joint, I try to move the flame around, from left side to bottom to right, etc., but maybe I'm doing this too fast? Sometimes an inch length of solder would break off and fall when I touched it to the joint, if that's any clue as to what is going on.

    So my main question is, because the solder didn't melt, is the only reason that it wasn't heated enough? The prep of the joint wouldn't have anything to do with whether the solder melts, would it? I'd think if it was prepped incorrectly, the solder would melt, but just not get sucked into the joint. Is it possible to have the joint too hot causing the solder not to melt? I saw that on another forum somewhere, where someone said if the joint is too hot, the solder won't melt, but that seems unlikely to me.

    I'll probably buy a MAPP torch to replace this propane one, but shouldn't a propane torch be adequate for non-pros who don't mind if it takes a bit longer? I'll get some Oatey solder too to replace the generic stuff, but I'm still curious as to what I'm doing wrong when the solder won't melt?
    Last edited by Studly; 06-28-2013 at 06:08 PM.

  2. #2
    Plumber MichaelBukay's Avatar
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    Default

    mapp or propane, if you clean the fittings and piping well, use a good flux, and there is no water in it, it should work. the only thing i can say is that sometimes if you get the fittings and piping too hot, the solder won't flow. just make sure the pipe and fitting are well cleaned.

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Default solder

    It is NOT he solder, since it HAS to melt at the correct temperature. IF you do not have water in the valve, then you may be using water soluble flux and "burning it. If so, the solder will still melt, but it will NOT flow into the joint.
    Licensed residential and commercial plumber

  4. #4
    DIY Member ImOld's Avatar
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    Default

    I would have to watch you to see the problem.

    Heat is applied where the two pieces are joined.

    The fact that you would apply heat for 10 minutes is scary!

    I'm sure you are doing damage.

    Any propane torch available in HD, Lowes, Ace, etc., will be sufficient and I have used them all over the years, without a problem on anything you can imagine.

    The previous poster gave you the basics and I would add that I like a nice full blast, sharp, blue, flame, moved completely around the joint.

    Heat is applied to the joint, not the solder.

    Solder should flow into the joint in a matter of seconds if all is done correctly.

  5. #5
    In the Trades Gary Swart's Avatar
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    Default

    I suspect you are burning the flux off. You should not have to apply that much heat for so long. Your propane torch is plenty. Sure, MAPP gas is hotter so faster, and that would be a factor if you were a pro sweating joints all day long, but for a typical DIY, the time saved is nothing.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Default Mapp

    As an aside, there is NO MAPP gas anymore. The plant burned down/blew up a couple of years ago, and the "yellow tanks" now are a substitute which is about 300 degrees less than true MAPP.
    Licensed residential and commercial plumber

  7. #7
    Jack of all trades DonL's Avatar
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    Default

    You need mapp gas or acetylene if you want to get with the program.

    The Flux should have nothing to do with it, like hj pointed out the solder will still melt, it just will not flow correct.

    You may be using a High Temp solder, and you need the Gas that matches its spec.

    Or your torch orifice needs cleaned, to get the proper fuel mixture.


    Good Luck.
    Theory only works perfect in a vacuum.

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  8. #8
    DIY Junior Member Studly's Avatar
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    Default

    Thanks for the tips everyone. Since when the solder does melt, it flows into the joint, I think my cleaning and prep are OK. But now that you confirm that if the joint it hot enough, it'll definitely melt the solder, it must be my technique. Looking back, maybe I'm not heating the joint evenly. I've always heated the bottom and sides of the joints more, figuring that heat rises and the top of the joint will get hot enough from the heat in the joint traveling up. That has worked fine for me in the past with thinner fittings, but with this big, thick brass shower valve, the heat likely spreads over a larger area. And since I'm usually concentrating the heat on the bottom and bottom-sides of the joint, then I'm usually touching the solder to the opposite side -- the top -- to see if it'll melt. So if the top is not hot enough, that is probably my problem.

    I have another shower valve to do and will make sure I spend even time heating all around the joint, not just the bottom and sides, and will see if that works better. But thanks for all the advice!
    Last edited by Studly; 06-29-2013 at 09:31 AM.

  9. #9
    DIY Junior Member Studly's Avatar
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    One other question: Do most of you apply solder to the opposite side of where the flame is on the joint? That's what I typically do to make sure the joint is thoroughly heated all the way around. Wondering if that only works on thinner fittings? If I have a thicker brass valve, like this shower valve where the heat gets spread out a lot, should I be pulling away the torch and applying solder to where I just had the flame, or work the flame around the joint slowly and apply solder just behind where the flame was?

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default

    If the joint is heated properly, it will make no difference where you apply the solder. If you only apply the solder where the flame is, you can create "cold joints" if it does not "merge" with the rest of the solder you put into the joint.
    Licensed residential and commercial plumber

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    If you're quick and you have things heated evenly, you no longer need the flame while adding the solder.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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