Buying Guide: Solders and Flux

For decades, copper pipe has been one of the most common materials used to distribute water throughout the home. The most common technique used to join sections of copper pipe is called soldering. 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 flux and solder appropriate for your project, so you can feel confident you’re getting the job done correctly.

Flux 
Flux may be made from organic or inorganic materials and is available in liquid and paste forms. 

Liquid flux features a strong cleaning agent which cleans oxidized copper. It is ideal for fast, effective soldering.

Paste flux cleans and fluxes simultaneously, is lead free and can be used on all metals except aluminum and stainless steel. Water-soluble paste flux is ideal for working with supply lines for drinking water.

Refer to the table below to identify the type of flux and solder you need.

Flux Type	Description	Points to Consider
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	For areas with high temperatures	Use the hot-weather formula in arid climates or on especially hot days
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 Standard B-813 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. Lead-free plumbing solders are required for use on pipes carrying drinking water, also known as potable water lines. The US Safe Water Drinking Act prohibits the use of leaded solders on lines carrying drinking water. Leaded solders are available for applications that will not come into contact with potable water, such as sheet metal repair, copper drain lines, etc.

Solder Type	Description	Points to Consider
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 or tin and lead	Use for sheet metal repair, copper drain lines, etc. 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, filling metal seams, etc. 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

Solder may also be used for a process similar to soldering called brazing, which requires its own special material and higher temperatures.

Brazing 
Brazing is another method for joining metal pipe pieces together. Hard solder, which is used for brazing, melts at higher temperatures and is available in various degrees of hardness. In general, soldering takes place at temperatures below 840° while brazing occurs at higher temperatures.

• Brazing is used when high joint strength is required.
• 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. 

As with any process that takes place at extremely high temperatures, there is equipment you can use and measures you can take to get the job done effectively and safely.

Safety 
Safety should always be one of your foremost concerns when soldering or brazing. Here are a few tips for getting the job done safely:

• 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, 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

Tools to Make Your Job Easier 

Tube Cutters 
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/Heat Shield 
If you’re heating a joint near combustible material, use a flame protector to shield the heat-sensitive material from damage.

Deburring Tool 
A 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.