Soldering Copper Water Lines

Copper doesn't rust. As such, it has become one of the preferred materials to use in residential water distribution systems. Copper, however, can corrode in certain circumstances.

Copper pipe and copper fittings are attached to one another by using solder. Solder is simply a metal, or combination of metals, that when heated bond to the copper. Think of the solder as a very permanent glue. Some metals which are used in solder are tin, antimony, silver and lead. Lead solder was used years ago because it flows at lower temperatures and is a "thicker" solder. Think of it as a maple syrup type solder. It has the capability to fill larger gaps between a pipe and a fitting in case the fit is sloppy. However, lead is poisonous! Don't use a solder that contains lead for water supply lines. It can be used safely for copper drainage lines. Look for solder that is often sold as "95-5". This is a solder that contains a mixture of tin and antimony. It is safe for water supply lines. Silver solder is often used for copper gas lines. It melts at a much higher temperature. The key to soldering is to get the surfaces which will be soldered clean. That's easy. You can use steel wool, sandpaper, plumber's cloth (a fancy sandpaper) and special wire brushes (for the inside of fittings) to accomplish this task. After they are clean, don't touch the cleaned areas! Dirt, grease, etc. from your fingers will spoil the solder job.

How to Solder Copper Pipe

Now apply flux evenly to the two pieces which are to be joined together. Flux is a chemical compound, frequently zinc chloride. It removes oxidation which allows solder to bond more easily to the copper. It is often sold as a paste that has the consistency of petroleum jelly. Always stir flux with a clean stick to thoroughly mix. If allowed to get warm or hot, the zinc chloride will separate from the paste.

Apply heat to the assembled fittings and pipe. Heat with a propane or acetylene torch, being careful not to set adjacent combustible material on fire. Heat until the flux stops bubbling. Pull the torch away and touch the heated joint with the solder. It should begin to melt within two seconds. If not, heat again with the torch. If you heat the copper just right, the stored heat in the pipe and fitting will be more than enough to melt the solder. Applying heat with the torch WHILE soldering can give misleading results. The solder may melt at the edge of the joint, but not flow into the joint. Many an apprentice plumber and DIYer has found this out the hard way!

Repairs to existing copper lines are tougher. Existing lines need to be drained of all water. You simply can't solder pipes that contain water. The water absorbs too much heat and doesn't allow the pipe to get hot enough to melt the solder.

If you have to repair existing lines there is an easy way to drain the water lines. Turn the water off at your main shut off. Next, flush all toilets and open all valves everywhere as quickly as possible, starting at the top of your house. Go to the lowest faucet and open it and the water will flow to this low point suctioning much water from the lines.

If you have a persistent drip at the repair sight, use this trick as a last resort. Do all your prep work to the joints. Have everything ready to go, torch, solder, etc. Get a piece of white bread. Remove the crust. Make a ball of bread, firmly packed, slightly larger than the inner diameter of the pipe that is dripping. Insert the bread into the pipe and push it 4 to 6 inches away from the joint with a small stick. Quickly assemble the pipe, heat and solder. The bread should give you a 30 to 45 second window in which to solder.

Finally, always keep a bucket or two of water handy in the event you start a fire. I have used it on more than one occasion!