View Full Version : How to fix bad solder joints?

03-21-2005, 09:10 AM
I have just spent a weekend running copper lines for a small house. First time soldering. I tested the cold line only, it resulted in a monsoon in the basement. Had several large leaks. I have fixed about half of them.

My dilemma is this. I ran the hot and cold lines at the same time. The cold line failed in many locations. I do not have water in the hot line. I have obvious reason to believe the hot lines will leak just as much.

Is there anything I can do to the hot line solders to try and reinforce the joints before I fill the lines with water and add the "water in the lines" dimension to fixing the joints?

A co-worker told me his father used some kind of liquid to coat the outside of an existing soldered joint, heated the joint, hit it with solder and it sealed the joint. The problem is he doesn't remember what the liquid is and his father is dead........does such an product exist?


03-21-2005, 10:03 AM
There isn't anything you put over the fittings, it's what is inside.
Did you use flux on the pipe?
To solder, you need clean pipe, pipe cleaner (flux) and even heat.

If the heat on the fitting and pipe is uneven, the solder will not flow all the way around.

03-21-2005, 10:14 AM
Thanks Terry.

Like I said I am not experienced, therefore I was not very disciplined in all the aspects. I skimped on flux in some spots. The even heat was another problem. All these little details have bitten me in the butt. The only thing I know I did well every time was clean the joints.

Knowing that my technique was less than stellar on the hot line, what do you suggest I do before I test it? Anything? Should I just go with it and fix the damage as it appears?

03-21-2005, 10:26 AM
If you have not added water yet, I would consider reheating joints that look bad. You can check around the fittings to see if the solder is beaded there.

If you have added water, the fitting will need to be removed and the process started over again.

03-21-2005, 01:07 PM
You may have a problem with the leaky joints in the cold water pipe, because once water enters a "bad joint" it contaminates the copper so the solder will not adhere to it, even though the surface of the joint where you put the solder is no longer leaking. Normally the only good repair to a joint that has leaked is to take it apart, reclean it, flux it and then put it back together and solder it properly. The hot water, since it has not had water in it, should not have the same problem, but unless you pressurize it with air, you will not know if you have any leaks or where they are, in which case you will have to "redo" all the joints, not just the ones that do not look good.

master plumber mark
03-22-2005, 06:34 PM
http://www.oatey.com/apps/catalog/instance_assets/images/catalog/productimages/95_lead_free_tinning.jpg (http://www.oatey.com/apps/catalog/showskus.asp?ctg=6&subctg=0&prodgrpid=76)

Oatey tinning flux in the plastic green jar (http://www.oatey.com/apps/catalog/showskus.asp?ctg=6&subctg=0&prodgrpid=76)is the absolute best for beginners...

and everyone at any level

Its water souluable and also completely tins the whole joint for you......

I have soldered for 40 years and dont really need to use it, but I still do

because it definitely gives you an extra "edje" and you absolutlely know

you arent going to have any leaks. whatsoever.

03-24-2005, 05:16 AM
I was looking at the Oateys No. 95 Tinning flux last night. I have been using Oateys No. 5. It appears the No. 95 contains flux and solder mixed? I was at Home Cheapo and of course nobody really new what the difference was between the two, except that they were different.


Gary Swart
03-24-2005, 08:21 AM
I've used mostly paste flux of various brands and once I used the water based type. I didn't really care much for the latter, but it worked. I don't know how really important the type of flux is for a DYIer, but without flux solder won't work. The main points of soldering are to clean the surfaces well immediately before applying flux, insert the pipe fully into the fitting, apply heat evenly around the joint until the joint is hot enough to melt the solder, keep the joint immobile while it cools naturally (no water added). Skimp or cheat on any of these steps can give a bad joint.

05-15-2005, 05:36 PM
What kind of torch is suggested? I had difficulty with the blue propane tank getting the copper hot enough to melt the solder without the flame on the fitting.

05-15-2005, 06:16 PM
Just put the flame on the fitting.

I keep a water spray bottle handy.
1) I can cool the fitting quicker after it's been soldered.
2) I can wet down the wood or drywall before I solder
3) Helps to put out small fires
4) I can cool off my burning hands when I forget how hot that thing is or if I find there is a hole in my glove when I wipe the pipe and fitting down afterwards .

by the way, I don't get the pipe wet before I solder, only after they've "been" soldered.
If water hurt pipes after they have been soldered, we would be in serious trouble. They are water lines, right?

05-16-2005, 12:52 AM
Once water has been introduced to the line, or if it already exists in ANY amount it makes the sweating of copper joints much more difficult. I absolutely hate sweating wet copper, as long as I've been doing this. Master Plumber Mark is right in recommending #95, as it has solder in it and tins the copper as it approaches the temp needed for a good joint. It is good stuff.

Propane is only good, in my lowly experience, for sweating absolutely dry copper such as you would have in a new construction house or remodel. Better if you spent a few more dollars on the yellow cannister of MAPP gas. It's hotter and solders better. I use it almost exclusively, since I do mostly work on older systems. If you have a really bad case, then it's time to resort to Oxygen/Acetylene mix and a brazing rod. But that is absolutely the last resort.

Never listen to the folks at Home Depot or especially Lowe's. They have no clue. I once asked them for a fish tape as I was wiring new garage lights. He took me to the aisle where they stocked Duct Tape...

05-16-2005, 08:53 AM
I did all of my connections outside at a work bench taking alot of time to do them properly. I only had to do two in place and one leaked. Luckily, somehow I was able to re-solder the connection without taking it apart. So far so good but I will invest in a yellow tank.

05-18-2005, 02:46 AM
Resoldering a joint is an iffy thing. Sometimes you can do it and sometimes you can't - more often than not. I'm glad you got it. It's more easy just to toss the fitting, use a new one and resurface the previously solder tinned pipe that you have been trying to solder. The new fitting will fit and sweat better.

05-28-2005, 02:22 AM
I just discovered the greatest thing since sliced bread. I've been doing a lot of A/C work lately and we all know that you can't use a soft solder in that application. I was buying Teensy copper/phosphorus brazing rods at a local Depot type home center for way too much money. While at a welding supplier I picked up some hefty silver brazing rods and a phosphate based flux. Works great on A/C units with my Oxy/Acetelyne setup, so I thought I'd try it in a plumbing situation on some 'wet' copper (older and with water in the lines.) It worked like magic! I've always used MAPP gas because it is hotter than propane and was always worried that oxy/acetelyne would be WAY too hot to the point I would risk damaging the plumbing by melting a hole in it, but this stuff just flows into the joint like water and seals perfectly. Even in wet lines.

05-28-2005, 07:12 AM
There are two problems with brazing. First you will never be able to take the joint apart, and second the process of heating the fitting cherry red anneals it and weakens the fitting. You will find that afterwards the fitting can be bent or twisted almost anyway you want to, but it also makes it susceptible to cracking and breaking. But you will never have to worry about the joint coming apart.

05-29-2005, 03:14 PM
I think this is a related question: Is there a "trick" to taking apart an existing soldiered joint? Two times today I heated a joint (with MAPP gas) and tried to take it apart, to no avail. The joint was hot enough that I had to remove my fire-proof gloves because they were starting to smoke, and soldier outside the joint was quite liquid.

One of the joints I had to take apart was a soldier that I don't trust.... Light went out in the middle of soldiering, so there was a short delay before I got the soldier to the joint..... Is the absence of solider on the outside, except a bead at the bottom of the joint, a sure sign of a screwed-up job?

05-30-2005, 10:36 AM
You can always cut the section out and start over.

Any water in the pipe will prevent "even" heating and prevent the fittings from being removed.

05-31-2005, 05:53 AM
Thanks, in my various practice jobs, I finally yesterday managed to pull apart a soldered joint. I think my mistake has been overheating with the MAPP gas, this time I used it more gingerly. Not sure if I welded pipe and fitting previously or if it was just oxidation holding the joint, but I twisted with pliers until the pipes were like wet spaghetti. I think I can pull apart a soldered joint now, but I've given up on pulling a fitting off a pipe.

On the bright side, when I took apart that last joint, the solder was 100% into the fitting :D.