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Sweating Copper

by Bill McCaslin

Sweating copper is a pain in the neck for most home owners. But its worth it! You can do things with copper impossible by any other means. In old office buildings I've taken 1 1/2 in. malleable copper tubing, run fifty foot coils through a rolling mill so it's less than the thickness of the 3/8 to 7/16 floor lathing. I've run it under hand inlayed floors fit for a palace, insulated it with "Sockz cloth" at a dollar an inch, so heat wouldn't crack or separate the inlays, reformed sized and broached the ends to fit standard 3/4 in copper fittings and used a reducing fitting to 1/2 so someone in a wheelchair could have a toilet where he wanted it. A drain was handy but no water.

Keep all your repair copper and bronze fittings in a Tupper type plastic box with some old chopped up newspaper. If your stuff is dirty and corroded, in half a gallon of boiling hot water put one quart of white distilled vinegar, throw about a pound of your fittings and return to a boil, then simultaneously add 1/4 cup of Arm & Hammer Sodium Bicarbonate and 1/4 cup of Salt. This is going to boil like crazy so best to do it in a large bucket. Using a paint stick stir like mad! add more Sodium Bicarbonate and salt checking the color of your fittings. Once they are clean rinse with clean water dry in shop towels and lay out to sun dry. Whatever you do, if you have cleaned any threaded copper fittings rub the threads (screw in - screw out) with some steel wool "0" is a good choice.

When you begin your project, draw it out exactly, make sure you have more "L", "T", hoppers and "45° L" and "geegaw" fittings than required. Precut as much of the rigid tubing as you can and assemble those parts of it first. I assure you it is much more pleasant to sit at a picnic table drinking an icy cold Budweiser sweating copper like a jeweller making a ring.

"...and yes Ma'm... I would like another Budweiser, thank you! and thanks, your brownies are fantastic! Hummmm better to labor so than it is to labor long unseen, misunderstood and not appreciated under the stinking cold wet foundation of someone's house... where only God knows what has leaked out.

So, you already know the first rule of sweating copper. 

  1. Clean your fittings

  2. Pre-Sweat when you can.

Now what does it mean to pre-sweat. It means immediately after you've cleaned your fittings either old or new, you drop them, except for all the threaded ones of course, into a ripe solder pot . To know when to drop, you rake the top of the solder pot, there should be a film of rosin on top. Gaze at the mirror for a few seconds, if it is wet with rosin and does not discolor in 5 seconds but discolors within 20 seconds you're ready. Drop in your parts, stir with due diligence and kick on the afterburner for more heat. Keep adding resin as the mirror clouds. Dig down into the lead and stir the parts bring them to the surface to meet the resin, observe the mirror every 15 seconds. You want to go against the grain here by using Rosin ( or Resin) instead of acid flux. Don't forget to stir. In a pinch you can get Rosin at the pharmacy. Next thing after about five minutes of increased very high heat you want to pull all these puppies out of this very hot pot and with considerable care violently shake off all the excess solder. This is best done in a wire mesh stainless steel basket. It is very important that the fittings are covered with a thin layer of solder. If they have globs and stick together, you need to turn up the heat and do it again. Please be careful around a pot of hot metals. Please shake hot solder neither upon your person or your clothing. You have been warned.

"...and yes Ma'm... I
would like another
Budweiser, thank you!
and thanks, your
brownies are just
fantastic!" ...

In the design of a copper water system you should make a low point (drain) where the water goes into the heater that's the key. Somewhere close by there should be H & C Drains which are physically the absolute lowest points in your entire copper plumbing system. You should create vents at the highest points in your system, you may create additional vents in long runs which might not drain well without air. In my Library behind " The Letters of Horace Walpole" there are two little 1/2 in. gate valves that vent both H & C to the air, facilitating the draining process. Their risers go to the roof so accidental actions do not result in water in the house. Drains and vents help you greatly when you have to repair or modify a copper installation. Do consider too, making close union fittings on valves. Always use gate valves which aren't likely to wear out. Gate valves should be either open or closed and nothing in-between. Do not use a Gate valve to control the flow of water. If you keep a spare unit, when a Gate valve begins to leak you can unscrew the union fittings and replace that puppy in five minutes. No solder no sweat! All I've got to say about washer valves is that I don't like them. In my opinion valves should not be used to moderate the flow of water, that's what faucets are for.

How to Sweat copper. Clean the ends of rigid copper with a stainless steel wool rubdown. Either paint or dip the surface in a pudding or liquid resin flux put a cold torch (propane) to the largest piece close to but not on top of the place you want to join do not heat a previously joined fitting. When hot wet it with lead. wasting no time clean it with steel wool "#0" is good for this.

Take a pre-tinned part in a pair of slip-joints, align them as close as you can. Heat both pieces by switching quickly one to the other. When you see all the lead melted continue to heat for 15 seconds, then gently join the pieces. They should go together like Romeo and Juliet! Once joined, continue to heat for 15 seconds. Now take a piece of bar solder and continuing the heat rub this against the joint. When the joint will not accept solder you're done. Never under any circumstances cool a sweat copper joint with a wet rag or with water. Don't move anything until the solder has set otherwise you'll likely have a leak.

In less than ideal circumstances when you can not control the flow of leaking water you'll not sweat a darn thing. I've used the skin off KFC original recipe, KFC biscuits, white bread, or toilet tissue to plug a pipe so I could sweat the job. Bread is the best as it readily breaks down when water pressure is applied. Before you apply pressure be sure you remove or bypass all water filters including faucet strainers. Once the water has run sufficiently to clear out anything that might be in the pipes, return your filters to normal and put the strainers back in.

Support fittings are available which will rigidly suspend copper plumbing 4 inches from the wall when copper is exposed as with heating and radiators or in institutional plumbing where there are service corridors and inspection ways. These fittings facilitate the modification or repair of copper lines since they greatly reduce the incidence of damage to paint, woodwork or wallboards due to accidental heating.

Whether you're building a new home, renovating or just fixin' up, you should seriously consider copper. Copper will supply clean water, it won't corrode or rot, is easy to repair if installed properly and is more resistant to freezing than PVC. Copper is malleable and can be formed into complicated shapes when the job requires. Copper will do things impossible with PVC or Iron.

Advice for Mr. Fix-It. if you're 30 and building your home with Iron pipe, just remember in most parts of the States, in about 35 years you'll probably have to re-tube the house. That means when you're 65, do you really want to take on that job and if not, do you want to pay for it? With copper you'll never have to re-tube.

There has been a lot of exposure about lead in drinking water plumbing. Proper application of solder to copper does not result in a lead problem. The key is this, wet the joint but don't make it drip. Be easy with your hand. - 

From: "Bill-McCaslin"

Nice site! Hi Good site, but I disagree with one of your statements: "With copper you'll never have to re-tube. "

This just isn't true. In my experience (as a plumber in the UK), untouched copper pipework will generally leak within 15 years of installation. This is most often caused by flux residues on or near soldered joints, but in all pipework the copper gradually wears away and a leak can occur anywhere.

The degree and type wear differs, of course, between cold supplies and, for example, wet central heating pipes. In the former the minerals passing through the pipe acts abrasively, and in the latter the repeated expansion and contraction causes work hardening of the copper and also stresses the joints.

Another factor is that few installations not lie untouched for 15 years - additional runs and styling changes in basins and such like will require joints between new and old pipework. If the old pipe is very old then it is invariably very thin, and when nearing its retirement it doesn't always withstand the forces involved in making a joint.

Just thought you'd like to know :) Kind regards Tim 29 Mar 2005

More from Bill on Sweating Copper

I know where you are coming from. Most copper plumbing is sweated with acid flux which leaves a corrosive residue both in the solder and on the surface. Even if you clean the joints with bicarbonate of soda, you still do not get all of the acid and, yes those joints will fail. That is why I recommend the use of Rosin or Resin flux.

On the other matter of the erosion of pipes internally, this is generally not a problem Stateside as we have very high standards regarding the contents of the Municipal water sources. But, in rural or unincorporated areas which do not maintain a competent Water Control Board, when the water source is not managed by a public utility or is a private well, and you have no way to control the mineral content or the PH, (relative acidity) then the problems you describe are exactly precise regardless of the flux used. -- "Bill McCaslin"


Pre-Sweating you are recommending 80/20 lead solder that is illegal in most states except the places where there so stupid from lead brain damage. dude!!! -- mark plantxinfo 19/02/10

More interesting articles by by Bill McCaslin:-

Ensuring the disabled have power
Mild retribution for the nasty ones
Don't put up with it
Don't let Spyware ruin your day

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Mending fences is often more productive than building walls - Axel Klystrom

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