copper half round gutter with rectangular downspout
copper half round gutter with rectangular downspout

So, you finally landed a copper job but you don’t know how to solder. Or, maybe you keep your costs down by using caulk on your copper instead of solder, and pass the savings on to the homeowner, right? This is usually a recipe for costly repairs down the road. Pro Tip: Do it right the first time, and use solder. Here’s how I’ve seen this scenario play out in the past. Contractor hires low-bid seamless gutter subcontractor to install new copper gutters. Seamless gutter subcontractor installs new copper gutters, and they look great. Everybody is happy until a year later when all of the joint start to leak. Contractor or homeowner hires a sub with soldering experience to peel out the failing caulk, grind the patina from the joints (we will go over this process later), flux and finally solder.

I’ve read a couple of theories about why caulk won’t adhere to copper, including oily residue or that the very beginning stages of patina prevent the caulk from adhering. Personal experience with both galvanized steel and copper make me think it’s a combination of both.

What Sealants Can Be Used With Copper?

Copper Development Association recommends elastomeric polyurethane sealants for “joints that are primarily designed to accommodate thermal movement of the copper,” so NP-1 or Vulkem would work. Nitrile based sealants like Lucas Gutter Seal should be avoided. The manufacturer should test the sealant specifically for use on copper and indicate that their product is appropriate. A compatible sealant still may require the use of a chemical or solution that compatible with copper that can remove the oily residue on the copper left over form the manufacturing process. By the you do this, why not learn to solder? Okay, let’s assume that you’ve found a sealant that works for you, and you haven’t had any callbacks and you’ve been “using caulk on copper gutters for years without any issues.” The potentially 100 year copper gutter installation is being sabotaged by a product that is only rated to last a fraction of that time. Don’t install a gutter system that is manufactured to fail.

How To Repair Copper Gutters That Have Been Caulked

There are three main steps to repairing copper gutters that have been caulked:

  • Remove the caulk at the end caps, outlets, and miters. Chances are, the sealant will pull out easily. If some of it sticks, don’t worry. See next step.
  • Usiffng an angle grinder fitted with a flap disk, start to clean o any remaining caulk and remove all patina from the areas being soldered. It’s very important for a strong solder joint to remove the brown patina finish and expose the raw shiny copper. Start with a very smooth grit. It usually does not require much force to accomplish your goal so take it easy and be careful not to grind through the copper. Always where gloves and eye protection, and be safe!
  • Properly flux and solder the joints. I won’t go into proper soldering techniques here, but I will say to make sure the joints are free and clear of caulk and any residual dust that resulted from grinding out the joints.
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