Flashing a Chimney With Soldered Copper — JLC Online

Flashing a Chimney With Soldered Copper - JLC Online

Traditional methods and materials prevent leaks for the life of the structure

We’re a third-generation custom building company here on Long Island. Back when the business was founded, tinsmiths generally installed all of a building’s flashing — window pans and heads, aprons, dormers, valleys, vents, gutters, chimneys. You name it, they flashed it, using sheet copper and traditional soldering methods.

Today most builders use lead to flash their chimneys, because it’s easy to work with and masons are used to installing it. But lead has its share of drawbacks: Folded corners create bulges that you have to work around, and the seams rely on caulking for a seal. Also, lead can tear at the worst possible moment — when you’re gently hammering it into shape, or during a reroof because it’s worn thin from corrosion. When that happens, the best option is to start over, but it’s more common for the roofer to break out the caulking gun.

For these reasons, we still rely exclusively on copper flashing. Soldered copper provides a long-lasting seamless barrier against water entry, plus it looks great. In this article, we’ll look at a job we do from time to time: a midslope chimney backed with a cricket.

Materials of Choice

We use lead-coated copper for a couple of reasons. First, most of the houses we build are right off Long Island Sound, where the salt air seems to wear out uncoated red copper too quickly. Second, the oils in western red cedar roof shingles can stain red copper, marring the overall appearance of the job. (Under other conditions, however, red copper is extremely long-lasting and typically develops that desirable verdigris patina seen on fine old work.)

As you may have heard, the price of copper has nearly quadrupled over the past five years; in just the last year, it’s doubled from about $2 to $4 per pound. That surely places copper on the chopping block for many construction budgets, but so far the high-end market we serve is taking the price increase in stride.

Soldering Tips

In concept, soldering copper is a simple procedure, and a skilled tinsmith can make it look easy. As with any skill, proficiency requires practice, but anyone who follows a few basic rules can get the hang of it.

Flashing a Chimney With Soldered Copper - JLC Online

To begin with, the metal must be chemically clean — free of corrosion (oxides) and surface contaminants like dirt and grease. Cleaning is done with flux. There are many flux formulations, to match different applications; for sheet copper, we use a zinc-chloride/ammonium-chloride blend.

The parts to be soldered must be held in firm contact with each other, either with weights or by clamping. If expansion and contraction are likely to stress a joint, it’s best to form a mechanical connection first, then solder it. Make sure the solder matches the metal; for copper flashing, we use a 65-35 tin-lead alloy.

Before soldering, the iron tip should be “tinned” — covered with a thin coating of solder — to ensure good, even heat transmission. Melt the solder by touching it to the heated metal, not to the iron. Don’t overheat or you’ll get contamination from oxidation of the iron; red-hot is too hot. Once you start, solder continuously and rapidly to avoid oxidation. And since it’s corrosive, clean the flux residue from the surrounding metal immediately after soldering, using warm water.

Before soldering, author John Seifert tins the copper tip: He rubs it on a soft brick to clean it.

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