How to Solder Copper Tubing
Solder copper - You do this when you melt solid solder and allow it to flow into the tiny gap between the tubing and the fitting. The red arrows point to the silver-colored solder. Copyright 2018 Tim Carter
How To Solder Copper Tubing - It's Really Easy
Revised February 2018
I’ve been a master plumber for nearly thirty years, but you don’t even have to have one day of apprentice school under your belt to be able to solder a simple joint in standard copper tubing.
Successful soldering is just a matter of understanding basic chemistry and having a few very affordable tools. It also helps to practice on a few pieces of tubing before you try to advance to a real pipe that will carry water. If you do decide to work on your water lines, be sure you’re allowed to do it. Some cities and states forbid homeowners from working on their own plumbing.
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You can watch a nice short video of me showing how to solder copper tubing by going here:
http://go.askthebuilder.com/soldercopper
The Degree of Difficulty: 
Step One: You’ll need a simple propane torch, a tubing cutter, some abrasive plumber’s cloth or sandpaper, a round wire fitting brush that matches the diameter of the pipe size you’re working with, four ounces of lead-free solder, and some soldering paste or flux. You’ll also need a few feet of half-inch-diameter copper tubing and some matching diameter 90-degree elbows to practice your technique.
Step Two: Cut a small length of copper tubing about 12 inches long. Use the tubing cutter making sure you don’t tighten it too tight so as to flatten the round copper tubing. Once cut, use the sandpaper or plumber’s cloth to clean off any oxidation from the copper tubing. You want the copper to look bright and shiny. Do NOT touch the end of the copper with your hands once clean. The oil and dirt from your hands can contaminate the copper.
Step Three: Use the small wire fitting brush to clean the oxidation off the inside of the 90-degree fitting. Twist the brush in the fitting back and forth to make the copper bright and shiny just like the tubing. Use the wire brush to also clean the narrow edge of the copper fitting. This is a secret tip most don’t know about.
Step Four: Open the soldering paste or flux and stir it up with a clean wood stick. If the flux is allowed to get hot, it can separate in the bottle or container. It must be mixed thoroughly before applying to the copper tubing and fitting.
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Step Five: Apply a thin coating of the flux to the bright copper tubing and inside of the fitting and push the tubing all the way into the fitting. Put the tubing on the edge of your workbench or outdoors on an old brick or something that’s not flammable. Lay something on the other end of the tubing so the pipe and fitting will not move as you solder.
Step Six: Light up the propane torch and adjust the flame to medium or medium-high. Make sure nothing is around you that can catch fire from the torch. Have a bucket of water handy in case a fire does start.
Step Seven: Apply heat to the pipe and fitting allowing the blue-white tip of the torch to contact the copper. Move the torch around the fitting and pipe for about 20 seconds. Do not introduce the solder to the copper during this time.
Step Eight: After heating the copper, remove the torch from the copper. Touch the end of the solder to the joint where the tubing enters the fitting. If the pipe is hot enough, the solder will begin to melt and flow within two seconds. If this doesn’t happen, take the solder away and re-apply the heat with the torch. Once the pipe is hot enough and the solder flows, you only have to apply the solder for about three seconds to have enough to fill the joint between the pipe and the fitting. Do NOT touch the pipe after soldering with your bare hands. It will be very hot and can cause severe burns.
Summary: The biggest mistake most beginners make is putting the solder onto the copper in the presence of the torch. The solder will melt, but not flow into the joint because the copper is not hot yet. You’ll think you have a great joint, but it’s a leaker. Also, if you don’t mix up the flux, the torch will burn the flux onto the pipe and you’ll have a blackened mess!
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