Soldering is a metalworking process that joins metals together with solder via heat. Solder is a filler, nonferrous metal that melts at a temperature below 840 F below that of the metals to be joined. After heating and melting, it hardens quickly, which secures it to the steel. The filler metal is distributed between the closely fitted surfaces of the joint by capillary attraction.
Matching metal and this mainstay metallurgical medium
Soldering, with regards to roofing, joins two pieces of metal together to create a durable and leakproof seam. “Soldering can be a controversial topic as many age-old European details look for folding techniques that require no solder,” say Tom and Jeff Stortz, John Stortz & Son, Philadelphia. “Even still, soldering is an efficient, quick method of creating watertight seams. Frequently soldered areas of a roof include soil pipes, chimney flashings, and protrusions or seams in a valley, gussets or diverter areas. All of these are spots that have high potential to leak or have water buildup.”
James Walas, architectural manager at Revere Copper Products Inc., Rome, N.Y., agrees that many critical junctures require soldered connections to ensure that the system remains rigid or watertight, such as areas of low-slope or flat roofs, the joints in coping covers, around roof penetrations such as chimneys, service entrances and within gutters. “These conditions require an experienced craft person,” he adds.
Prepare steel surfaces with a steel wire brush or steel wool by agitating or scrubbing the surface vigorously. “Mechanically abrade the joining area and fit all copper pieces tightly together, a 0.004- to 0.007-inch gap is optimal,” says Stephen Knapp, director of sheet, strip and plate for theCopper Development Association, New York City. Metals being joined have to be cleaned to remove any, dirt, corrosion, oil, grease, films or oxides. Solder will not adhere to oxides.
Also, a flux agent can ensure a complete bond and full strength at the joints. Liquid soldering flux is a mixture of inorganic salts in water. Fluxes clean the joint area, prevent oxidations, increase the wetting power of the solder by decreasing surface tension, and allow the solder to correctly flow and fill the intended joint. Rosin and organic fluxes do not consistently break the oxide coating. Use an acid flux designed to solder steel. The correct flux depends on the material being soldering. Certain metals will require a more aggressive or acidic flux to achieve a proper joint.
A fully sweated watertight seam is not possible if a cleaned seam is exposed to the atmosphere for more than a few hours, is damp, or contains dirt or oils. “Removing oxidation just prior to fluxing and soldering is a critical factor to proper soldering,” Knapp says. “Only prepare the amount of pans that can be completed in the current day.”
Knapp says fluxes ensure that the soldering bar is kept clean too. “Solder works best when it is free from impurities,” he says. “Occasionally dipping the tip of the soldering copper in flux solution will clean off excess oxidation. Once completed, if necessary, immediately flux and re-solder any areas where solder appears to not have filled the seam. Then clean off the joint and neutralize any flux as excessive residual flux will discolor copper.”
Soldering exposes workers to hazards, including very hot materials. When soldering and handling the hot equipment and receptacles such as quenching buckets, wear gloves, goggles or safety glasses, long-sleeved shirts and other devices designed to prevent burns and eye injuries. Work in a well-ventilated area.
“Safety equipment is critical since some of the components used, such as heated flux and molten solders, can ‘spit’ when in a liquid form, especially when too hot,” Knapp says. “Fume exposure, on the other hand, is greatly mitigated due to the nature of most copper architectural applications being outdoors, which provides for natural ventilation.” Tom and Jeff Stortz stress safety precautions always be a top priority when soldering, even advising that having water nearby is good practice. “Fire is a major concern when soldering metal roofs,” they say. “Using an open-flame torch is generally frowned upon in the industry as it increases potential for a fire. Enclosed-flame torches lessen the risk and direct the heat source away from the roofs surface. Always have a fire extinguisher accessible on-site, and give a 30-minute fire watch once completed. Another risk is inhaling toxic chemicals.”
Soldering Technique and Tips
Blind soldering minimizes exposed solder in finished joints. To do this, “Solder is applied to the back or concealed edge of copper surfaces,” Walas says. “The solder often used is common 50/50 tin-lead bar solder for uncoated copper. Alternative tin-based solders are available for those who prefer a lead-free installation. Continuous, long runs of soldered seams should be avoided to limit stress fractures.”
Lead-free options, which are primarily tin-based, are available for lead-free applications. However, these materials have a higher melting point and are less workable, especially at cooler ambient temperatures. “While lead-free solders are required in certain plumbing applications where the solder comes in contact with potable water, 50/50 tin-lead solder is still the preferred choice for roofing and architectural applications,” Walas says. “It is durable, has excellent flow and formability characteristics, and has excellent strength when installed properly.”
Another important soldering technique involves consistent heating. “Lack of proper heating results in seams that are only partially filled and will leak or crack,” Knapp says.
“Heating the back side of the seam away from the opening helps ensure the solder pulls completely through the seam.” Also, for correct roof soldering, don’t use flat locked and soldered pans that exceed the maximum cross-section recommendations. Knapp says this often leads to stressed and cracked seams. Use a maximum cross section of 18 by 24 inches, edges tinned 1 1/2 to 1 3/4 inches, prior to forming the 3/4-inch seams.