How to Solder Copper Into a Shower Mixer

With the exception of aluminum and zinc alloys, soldering is the easiest way to join various metals without resorting to fusion welding. However, since lead is ductile, soldered joints are not strong enough to withstand heavy shear or tensile stresses. On the other hand, correctly applied solder produces a watertight joint and has outstanding conductivity when used on electrical connections. When joining plumbing fixtures, such as installing a shower mixer, successful soldering relies on three factors: oxide-free mating surfaces, an effective flux and heating the parent metal to a point where the metal itself is hot enough to melt solder.

Emery cloth
Paste soldering flux
Heavy workman’s gloves
Plumber’s propane soldering torch
Wire solder
Heavy rag

Instructions

- 1
  Disassemble the shower mixer as directed in the manufacturer’s instructions and remove all rubber seals, non-metal parts and the mixer diverter cartridge.
- 2
  Roll up a tube of emery cloth and use it to scour the inside faces of all inlet and outlet ports to be soldered. Ensure that the brass mating surface is shiny and clear of any oxidation.
- 3
  Clean an inch-long section on the ends of all copper pipes to be soldered to the shower mixer with a strip of emery cloth. Avoid touching any prepared surfaces with your fingers.
- 4
  Coat all mating inside and outside surfaces with a layer of paste soldering flux and insert the prepared copper pipes into the inlet and outlet ports on the mixer, with the outlet arrow on the mixer body pointing up toward the shower head.
- 5
  Place a piece of sheet metal between nearby combustible surfaces and the fitting.
- 6
  Don a pair of heavy workman’s gloves and light a plumber’s propane soldering torch. Hold the tip of the inner blue cone of the flame against the mixer body and play the flame back and forth to heat the body near one of the ports, not the pipes. Do not play the flame over the layer of paste flux surrounding the joints.
- 7
  Play the flame over the copper pipe near the joint to be soldered as soon as the flux starts to melt. Heat until the copper starts to turn blue/black and the flux has liquefied completely.
- 8
  Concentrate the flame on the mixer body once the flux has melted. Feed enough wire solder into the joint so that capillary attraction draws molten solder all the way around the pipe where it meets the mixer body. Remove the flame and wipe the joint clean with a heavy rag before the solder solidifies.
- 9
  Repeat by soldering the rest of the joints the same way.
- 10
  Allow the unit to air cool and reassemble the shower mixer valve. Turn on the water and check for leaks.

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