If you have a copper pipe that needs a soldered, you may have trouble keeping the moisture out. Moisture and solder do not mix well. Solder can only be applied to a dry pipe and soldering a wet copper pipe is made easy with a few simple preparations.
Step 1 - Shut Off Water
Find the main water valve in your house and shut it off. The main water valve is located by the water meter which is usually outside the house. Turn the valve until it stops.
Fill a bucket with water and put a shop rag in it. You should also have a fire extinguisher within reach. You will be working with fire possibly directly under wooden rafters. If a fire starts, use the bucket of water first to attempt to put it out. However, if that doesn't work, use the extinguisher. You need to wear your safety glasses because if too much solder is applied, it can splash. Keep your eyes safe, especially if you are working above eye level.
Step 2 - Stop Moisture
Plumbers Bread is a cornstarch based moisture stopper. It will stop the moisture in the pipe and dissolve when the water flow is turned back on. Follow the directions on the Plumbers Bread closely and put it in the side of the pipe the leak is coming from or all the pipes that will be connected to the fitting.
Step 3 - Prepare the Pipe and Fitting
There should be no sharp edges. Cut sandpaper into a 1-inch strip and sand the ends of the cut pipe until it is polished and shiny. Make sure to sand all the way around and apply a thin coat of flux using an application brush to the outside of the pipe ends and inside of fitting. A thin layer of flux will prevent oxidation but too much flux will cause oxidation. Wear gloves when using flux because the chemicals in flux can damage your skin and eyes.
Step 4 - Place Fitting
Assemble the fitting onto the pipes and make sure it is tight.
Light the torch. Start on a low flame, then increase the size of the flame. Apply heat to the joint and move the flame around the joint consistently to evenly heat the fitting.
Step 5 - Solder the Joint
Once the joint starts to become a greenish color, test the temperature by touching the end of your solder to the joint. If the solder melts, it is ready to be applied. You can either apply the tip of the solder to the top of the joint and allow the solder to melt and flow around the seam of the joint or you can wrap the solder around the seam and let it melt.
Next wring out the shop rag in the bucket and gently wipe the joint so the solder is smooth. Take special caution not to move the joint while gently wiping.