Step 5 · Solder the New Connections
Once everything is dry-fitted, disassemble the connections. Thoroughly clean the outside of the pipe ends and the inside of the fittings using a pipe cleaning brush and emery cloth until the copper is shiny. Apply a thin layer of water-soluble flux to all surfaces to be joined. Reassemble the pipes and fittings. Using a propane or MAPP gas torch, heat the joint evenly. When the flux sizzles, touch the lead-free solder to the opposite side of the joint from the flame. The heat will draw the solder into the joint, creating a seal. You will see a silver ring appear when the joint is full. Repeat for all connections: hot in, cold in, shower riser out, and tub spout out. Use a flame shield to protect the wood framing from the torch flame. Make sure the valve's cartridge is removed before soldering, as the heat can damage it.