Q&A / 

Solder Tips for Copper Tubing

Soldering Copper Tubing Tips

To solder copper pipe you must heat the copper pipe and the fitting to be soldered to a sufficient temperature. When the copper is hot enough, it will actually draw the solder into the joint by capillary attraction. Believe it or not, solder will actually flow uphill.

A simple propane torch that uses screw on bottles will adequately solder pipe up to 3/4 inch in diameter. Plumbers generally use acetylene torches for two reasons. The acetylene burns hotter than propane allowing for faster solder times. The acetylene is available in larger tanks which attach to handy hoses and lightweight torches. If you want acetylene, you just need to go to a large plumbing supply house or a place that services welders.

Clean Pipe & Fittings

Solder, which is available in leaded an no lead versions, attaches to the pipe on a molecular level. The surface of the soldered joint actually becomes an alloy where the copper and solder intermix. For this to happen, the copper must be very clean and free of oxidation. You can clean copper pipe in any number of ways. You can use coarse steel wool, sandpaper and/or a wire brush. Special round wire brushes come in a variety of sizes to clean the inside of copper fittings and valves. Simply twist the brushes or pipe to clean them. Even if you purchase new copper pipe, it should also be cleaned. You only need to brighten the area which is to receive solder.

Flux - The Catalyst

Flux is a chemical which helps you solder. It actually finishes up the cleaning job you started with the sandpaper and brushes. In addition, it prevents the pipe from oxidizing as you heat it. You can solder without flux, but it is really difficult! Flux is applied to both the pipe and the fitting with a handy miniature paint brush. You do not need massive amounts to be effective. Besides, once you start to heat the pipe, 90 percent of it boils off and evaporates.

Solder - Different Types - Beware!

Solder is available in generally three types: 50 percent lead/50 percent tin; 95 percent tin-antimony/5 percent lead; and lead free solder.

Any water supply pipe should be soldered with solder that contains no more than 5 percent lead. If possible, use the lead free solder. The 50 percent lead solder is used for copper drain lines. It melts at a lower temperature and is able to bridge larger gaps as it cools. This is handy when working with large diameter (up to 4 inch!) copper pipe and fittings. You MUST pay attention when you buy solder. The 1 pound rolls look very much alike. Carefully look at the label as you might purchase the wrong one.

Lighting & Working with a Torch

Plumbing torches can be lit with matches, lighters or preferably a flint striker. Matches and lighters can be dangerous, as you might not put them out. A flint striker makes sparks which ignite the flame. Plus, a single flint in a striker can last a homeowner 10 years or more! Flame temperature is important. You need to set the flame on medium or high to generate enough heat to melt solder. If your flame is adjusted correctly, it will burn different shades of blue. You will notice at the center of the flame a darker blue section that comes to a point. This is the hottest part of the flame. You apply this part of the flame to the copper pipe.

Don't be afraid to heat both sides of the pipe. Rotate the torch around the joint for even heat distribution. When I use my acetylene torch and I am soldering 1/2 inch pipe, I can usually heat the pipe to the correct temperature in 10 seconds or less. A propane torch may take 15 to 20 seconds.

Always look beyond the pipe. Extremely hot temperatures are beyond the visible portions of the flame. You can easily scorch lumber or wires. If you are soldering near old lumber or in joist spaces near vertical walls, you can start your house on fire easily. Be careful and use flame shields. These are flame resistant fabrics or simple pieces of sheet metal which absorb and/or deflect the heat.

Click here to watch a video on soldering copper pipes and fittings.


Applying Solder

As you heat the pipe and fitting you will see the flux begin to boil and evaporate. Once the flux stops boiling the pipe is generally hot enough to solder. Move the torch away and touch the solder to the pipe. It may take 2 to 3 seconds for the solder to melt. If the pipe is horizontal, apply the solder to the top of the pipe. The solder will roll around in an instant. If you have done the job right, a droplet of solder will be at the bottom of the joint. You can flick this molten solder away with an old rag. Blowing on the joint will allow it to cool. It will be hot, but rub the joint quickly with an old rag to remove flux residue. This will also polish the solder. Check the joint closely to see if you see a silver colored band around the entire joint. If so, your first solder joint may be perfect. As I would say on a job, "Another quality installation!"

Column B353


Leave a Reply

You have to agree to the comment policy.