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5 Common Mistakes That Could Occur When Soldering Sheet Metal

5 Common Mistakes That Could Occur When Soldering Sheet Metal

When you are soldering sheet metal, it can be a relatively easy process once you have the training and practice down.  Of course, there are times when the soldering process goes smoothly and other times when the seams just don’t fit correctly.  Or the sheet metal pieces don’t hold together as they should.

Below are some ways to fix some of the common sheet metal soldering mistakes and to ensure a seamless soldering process.

1. The sheet metal pieces aren’t holding together

If the sheet metal pieces aren’t holding together, it could be simply that the steel surface was dirty before you started the soldering process.  It is important to have a clean surface for a good hold. 

Before starting the soldering process again, you should clean the sheet metal and remove the grease, oil or any dirt with a stainless steel brush and a cleaning solvent.  Right after you cleaned the surface, then start the soldering process immediately.

2. You re-soldered a broken seam (not a good idea!)

If you broke a seam while soldering, it’s always advisable to start the process over.  Don’t try to solder a broken seam.  If the joint is broken, dirt and moisture will enter the seam joint which will cause it to oxidize.  Just start the whole sheet metal soldering process over.

3. The solder isn’t sticking to the metal surface

If the solder isn’t sticking to the metal surface, the usual culprit is the wrong flux was used.  For stainless steel soldering, choosing the right flux is one of the most important aspects of the soldering process.

The best flux for stainless steel is a highly aggressive flux.  A high activity, phosphoric acid-based flux works the best due to the tenacious oxides that are typically on the stainless steel surface.  Use the appropriate flux for galvanized and solder parts.

4. The solder isn’t melting quickly enough

If the solder isn’t melting quickly enough while you are soldering, it could be three things: the soldering iron isn’t hot enough, the surfaces that you want to connect are too cold., or there’s no flux on the seam.

First pre-heat the soldering iron or torch that you are using.  Then pre-heat both steel surfaces that you want to connect with your soldering iron or torch.  Leave the torch or ion on the unit until it is sufficiently hot to melt the solder.   And then start soldering.

5. The joints aren’t holding properly

If the joints aren’t holding and you have tried all the above, it might simply be that you need a different type of solder.  There are many different tin-lead solders that can be used to solder copper, galvanized, or stainless steel.

Both leaded and lead-free solders will work if the metal joints are joined for mechanical strength prior to soldering.  When using lead-free, it is recommended to use the 97/3 tin/copper alloy as other lead-free alloys may be too brittle to withstand expansion and contraction under a weight load.

After you have correctly soldered the pieces and finished your work, it’s time to clean the pieces.  Clean the flux off as well as the solder joints.  Wipe the surface down with a damp cloth or flush with clean water to prevent corrosion. 


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