How to Solder Copper Gutters

Lightly sand the ends of the gutters you will be joining. Sand a 1 1/2-inch strip on the bottom side of the upstream gutter. Sand a 1 1/2-inch strip on the top side of the downstream gutter.

Remove sanding dust from both surfaces with a clean cloth. Apply acid flux to both sanded surfaces and press them together. The exposed edge of the seam should now be facing the downstream end of the gutter. Facing the butt-end of the seam downstream allows for a smoother water flow and reduces the risk of leaks.

Heat the soldering iron. The tip should be hot enough to melt solder before you apply it to the copper.

Press the tip of the soldering iron against the surface of the upstream gutter 1 inch above the seam.

Unroll a small amount of solder. Press the end of the solder lightly against the lip of the seam. When the solder melts, it will be wicked between the layers of copper. Move the solder and iron slowly along the seam until the entire seam has been covered.