How to Use Silver Solder

Silver solder is used to join brass, copper, tin and other materials by hard soldering, also known as silver soldering.  The main ingredient in silver solder is not silver -- only 25 percent of silver solder is actually silver -- but tin.

It is the silver that provides the solder its excellent free-flowing quality and makes it such a good sealant.  Silver solder is not an acceptable technique for gap-filling, however.

For silver soldering to work well, the pieces must already fit snugly. 

1. Dry-fit the pieces you plan to solder. Check that they fit snugly with each other before you start soldering. Remove any burrs from the end of the pieces. This is especially important if you are soldering the pipes of a refrigeration system, because burrs can disrupt the flow of the refrigerants and become noisy and inefficient.
2. Clean the inside of both pieces and your soldering tool's iron tip with a fibreglass filament brush. The silver solder will not take if the parts are not completely free from contamination.
3. Coat each fitting with paste flux. This will help keep them clean. Fit the pieces together. Start heating the joint and the surrounding area with the soldering flame. Move the flame evenly around the joint until the inner flame touching the fittings turns green. This will signal that you are ready to apply the silver soldering.
4. Apply the silver solder rod to the joint while you continue to concentrate the flame on the center of the fittings. You should see the silver solder spread easily around the joint. If it doesn't, it means the fittings were not hot enough. Apply the flame on the fittings until the silver solder covers the entire joint.
5. Wrap the joint with a cold rag. This will cool down the joint quickly and give you a shiny and professional-looking finish.