How to Select Flux and Solder

Use flux and solder to weld copper pipe joints safely and effectively

Flux and Solder - Select Flux and Solder

Copper pipe is one of the most common materials used to distribute water throughout the home, and copper pipes are typically joined to one another using flux and solder.

In the soldering process, heat is applied to the copper joint where the pipe and fitting meet and the gap between the joint is filled with molten metal.

This guide will help you identify the type of flux and solder that’s right for your project and teach you how to properly and safely use them.

Flux

Flux is used to join and clean metals. It is made from organic or inorganic materials and is available in liquid and paste forms.

Flux type Characteristics

Paste

  • Cleans and fluxes simultaneously
  • Lead-free
  • Removes surface oxidation from pipes
  • Can be used on all materials except aluminum and stainless steel

Tinning paste

  • Contains lead-free solder wire in powder form to clean and pre-tin the pipe surface and allow solder to easily draw into the joint
  • Ideal for use with large diameter copper pipe
  • Little expertise needed for effective use

Hot weather formula paste

  • Ideal for areas with high temperatures

Water soluble paste

  • Cleans and fluxes simultaneously
  • Ideal for working with supply lines for drinking water, copper, fire sprinklers and hydronic heating systems
  • Meets plumbing code ASTM B-813 standards for flux used in potable water systems
  • Meets plumbing code requirements for water flushable fluxes

Water soluble tinning paste

  • Contains lead-free solder wire in powder form to clean and pre-tin copper pipe surfaces and allow solder to easily draw into the joint
  • Won’t turn copper green
  • Meets ASTM B-813 standards and is approved for use by model plumbing code
  • Ideal for use with large diameter copper pipe
  • Little expertise needed for effective use

Liquid

  • Cleans the surface of pipes and prepares them for solder
  • Features a strong cleaning agent which cleans oxidized copper
  • Allows for fast, effective soldering

Solder

Solder is a metal alloy comprised of different elements. Solder may also be used for a process similar to soldering called brazing, which requires its own special material and higher temperatures than soldering.

The U.S. Safe Water Drinking Act prohibits the use of leaded solders on lines carrying drinking water. Lead-free plumbing solders are required for use on pipes carrying drinking water, also known as potable water lines.

Leaded solders are available for applications that will not come into contact with potable water, such as sheet metal repair or copper drain lines.

Lead-free

  • Typical alloys consist of either tin, copper, bismuth and silver, or tin and antimony
  • Use on pipes carrying drinking water
  • Must be used with external flux

Leaded solid wire

  • Typical alloy consists of tin and lead
  • Use for sheet metal repair and copper drain lines
  • Must be used with external flux
  • May be used for soldering or brazing
  • Not for use with potable water applications

Acid core wire

  • Typical alloy consists of tin and lead or tin and antimony
  • General purpose solder for repairing galvanized gutters and filling metal seams
  • Does not require external flux application
  • Not for use with potable water applications

Rosin core wire

  • Typical alloy consists of tin and lead or tin and antimony
  • Use for electrical applications, including wiring and other fine electronic work such as printed circuit boards
  • Does not require external flux application
  • Not for use with potable water applications

Brazing

Brazing is another method for joining metal pipe pieces together. In general, soldering takes place at temperatures below 840 F while brazing occurs at higher temperatures. Brazing is used when high joint strength is required.

Hard solder, which is used for brazing, melts at higher temperatures and is available in various degrees of hardness.

Brazing requires a different kind of flux and solder. The flux is formulated to withstand the higher temperatures associated with brazing. The filler is a different combination of metals that melt at a higher temperature and are stronger when cooled.

Safety

Safety should always be one of your foremost concerns when soldering or brazing. Always use fire retardant protection like a heat cloth or flame protection blanket when working around combustible elements like wood, drywall and insulation.

  • Keep a fire extinguisher nearby at all times.
  • Wear safety glasses, a helmet and protective gloves.
  • Wash off excess flux after soldering to prevent corrosion.
  • Do not use flux on electrical parts.
  • Use adequate ventilation when fluxing and soldering, particularly in close quarters.
  • Always refer to a professional in your area for codes or additional safety tips.

Helpful Tools

When soldering, there are several tools such as tube cutters, flame protectors and emery cloths that can help make your work look professional and keep you safe with working.

Tube cutters: Help ensure smooth, even cuts when working with plastic tubing, minimizing the amount of time you’ll have to spend sanding, and help ensure a better solder. 

Flame protector: If you’re heating a joint near combustible material, use a flame protector or heat shield to protect the heat-sensitive material from damage.

Deburring tool: Makes it much easier to remove burrs and rough edges from pipes once they’ve been cut.

Emery cloth: Use strips of emery cloth to clean and prepare copper pipe for the application of flux and solder.