Applying solder in electrical and plumbing applications requires a through preparation of the metal surface to ensure an effective bond. Solder is designed to join softer metals, such as copper, similarly to welding. Before solder is applied, a flux paste must be spread on all contact surfaces to allow the solder to adhere properly to the metal. For most plumbing applications a tinning flux, which has traces amounts of solder added to the paste to facilitate heat transfer, provides a superior bond over standard fluxes.
Things You'll Need
Coarse-grade steel wool
Lead-free tinning flux
Test-fit the pipes and coupler joint together. Make a mark on the pipes 1 inch past the ends of the coupling joint with a marking pen. Disassemble the pipes.
Scour the outsides of the pipes as well as the insides of the joint coupler with coarse-grade steel wool. Work the pipes thoroughly with the steel wool from the ends of the pipes to the pen mark.
Wipe the pipes and coupler with a clean cloth to remove any residue left by the steel wool. Coat the scoured ends of the pipes with tinning flux, with a brush, and assemble the pipes into the coupler.
Uncoil enough wire solder from the spool to wrap around the circumference of the pipe, once, and then straighten the solder out into a straight line.
Heat the edges of the joint, where the pipe meets the coupling, with the torch. Move the torch around the circumference of the joint, heating all areas of the joint evenly, for 30 seconds.
Hold the solder wire over the joint so the tip of the solder touches the top-center of the joint. Move the torch towards the solder just until the solder begins to melt. Allow the solder to run down along both sides of the joint until the molten solder begins to from a drop at the bottom of the joint.
Repeat the procedure on the opposite side of the coupling. Allow the solder to cool completely. Turn on the water and check the soldered joints for leaks.
Brass valve fittings require heating to higher temperatures than copper for the solder to properly adhere.
Flush pipes for five minutes after soldering new connections.