Credit and my thanks go to
Sweating Pipes
Many years ago I watched a neighbor working on his plumbing. He was working on copper pipes and had a torch in one hand, a roll of solder in the other, and a smile on his face. He obviously knew what he was doing. Now, I was just a kid but I had learned that when Mr. Fesmire was smiling you could learn things from him - when he was cussing and had a frown on his face he was doing things wrong and I kinda didn't hang around him. But he was smiling so I watched.
"The secret is in the sandpaper" he smiled as he stepped up on the stepladder. "Ya gotta clean the joints before you do anything else."
He was right. I watched as he heated an already cleaned and assembled elbow stuck on the end of a three foot length of 1/2 inch copper pipe. He heated it until it smoked then he just touched the wire solder to the seam where the elbow met the pipe and voila! The solder flowed into the joint - not only where he touched it, but all around the joint.
"Aren't you going to solder the other side of the joint? You only put solder in one spot?" . . .
"Well, maybe I'll just run a bit on the other side to make sure it covers the whole joint. Watch it flow - it's magic!!"
Well, it wasn't magic, it was capillary action. A techie term that says that a liquid will flow into a narrow opening due to its surface tension and its viscosity or some mumbo jumbo like that. But, it works. The secret is in the sandpaper though, because in order for capillary action to work the liquid has to wet the surface. With molten solder on copper that is called tinning the surface. One of the other elements in the sweat soldering process is to assure that after you clean the copper to a bright shine with the sandpaper you must prevent oxidation from happening while you heat the joint. Soldering paste, or flux, as it is sometimes called is the secret here. Never run out of flux. Buy yourself a three ounce tin of it and you will have it for your grandchildren. A little goes a long way. Just wipe it on the cleaned surfaces, both of them, before assembling the joint.
Every time I had tried sweat soldering (that's the plumbers name for it) a copper joint I would first "tin" the surfaces of the outside of the pipe and the inside of the fitting. Then I would heat both elements and wait until the solder was molten then push the two together. Then I would apply more solder until it started dripping from the joint! I was not only wasting time, I was wasting solder! Mind you now, none of the joints I fixed were ever found to be dripping, except on a rare occasion where I was working on a pipe that wasn't totally drained of water, which brings me to the next topic - water and sweat soldering don't get along, unless you have enough bread to make the difference.
Bread? Did he say bread? Yep, not dough, er money kinda bread. Real white bread, you know the soft white pap that all the kids are told are good for them! The kind that has all the nutrients bleached out of it so that all it does is go down easy - but I am drifting from the main subject here, sweat soldering. You see, one of the other major factors in sweat soldering beside the cleanliness of the joint is the ability to totally heat the joint - all the way around. I'm sure you have been here; you have turned the water off and opened the cellar faucet to drain the system. You have cut the pipes and are now ready to solder in the filter, or whatever it is you are putting in the line. You notice that even though you have drained the system there is still an occasional drip that comes from the end of the pipe that goes upstairs. Well, if you waited until all of the water drained out of all of the pipes you would probably be finishing the job the next day. So you figure that if you turn the torch waaaay up you will be able to heat the joint fast enough to evaporate any water dripping into the joint and finish the joint in time for supper. Wrongo! Even one drop of water running into the joint will ruin an otherwise picture perfect sweat solder joint. It will leak. It might not show up immediately, but sometime, probably while you are away on vacation, it will start squirting a needle thin stream of water right at your lathe and when you come home from that nice refreshing Florida vacation you will find a pile of rust where your Craftsman lathe used to be! Sooo, lissen up! Here's where the bread comes in. Get Johnny to go make himself a peanut butter sammich and bring it down to you where you are working. Eat the peanut butter and take that slice of white pap and roll it between your hands until it forms a doughball. Now you can't do this with a good whole wheat bread cuz it has too much good stuff in it to ball into a doughball, but that white bread works just super. Take that doughball and pack it into the pipe that goes upstairs. Take a piece of dowel and puuuush it back about a foot from where you are soldering. If you still haven't eaten the other slice do it with that one too. You will need more or less bread depending on how badly the water is dripping. The bread ball will form a blockage in the pipe, just like it does in your stomach, and prevent anything from getting past, just like it does in your stomach. For your stomach you can take a Rolaid or a Tums - for the pipe, just hurry up and finish your sweat soldering.
Finished soldering? Ok, go turn on the water supply and run, don't walk, to the cellar faucet you opened earlier. If you hurry you will see that wad of doughballed white bread come slurping out of the faucet and down the drain where it will do no one any harm. And your joint will NOT spring a leak the next time you are in Florida.
Now go to the store and buy a loaf of whole wheat bread and feed Johnny the good stuff . . . . .