Can You Weld Floor Pans with Flux Core?

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Key Takeaways:

  • Yes, flux core welding can be used to weld floor pans due to its portability and effectiveness on thin materials.
  • Proper machine setup, material prep, technique, and caution are crucial when flux core welding floor pans.
  • Spot welding is the recommended technique for welding floor pans to prevent warping and burning through.
  • Thorough cleaning and rust removal are vital before attempting to weld floor pans.
  • Practice first on scrap pieces of the same thickness until comfortable with settings and method.


For auto restoration projects or when repairing a rusted-out floor pan on a vehicle, a key question that arises is what welding process works best for joining thin sheet metal. Floor pans provide structural integrity to the underside of a vehicle and commonly range in thickness from 16 gauge to 22 gauge steel. Their thin profile means floor pans require a delicate welding approach to avoid unwanted burn-through.

So can you use flux core welding on floor pans? The answer is yes. With the right machine settings, material preparation, technique, and operator skill, flux core welding can be an effective process for successfully welding new floor pans in place. This comprehensive guide takes an in-depth look at considerations when using flux core specifically for thin floor pan welding applications. It analyzes proper methods, equipment, and techniques to help ensure high weld quality and prevent warping when taking on floor pan replacement.

With detailed information on machine setup, metal preparation, welding technique, and process best practices, readers will leave well-informed on executing flux core welds on floor pans. The ability to weld floor pans with flux core grants increased flexibility through its portable nature and effectiveness on thin stock. However, caution must be exercised to prevent burning through the delicate material. By following the recommendations outlined here, DIYers can gain confidence for welding floor pan replacement jobs safely with a flux core welder.

What is Flux Core Welding?

Before examining its use on floor pans, it helps first to understand what makes flux core welding unique. This process relies on a continuously fed wire electrode containing an inner core of fluxing agents. As the wire melts, the flux produces strong welds while also releasing shielding gases to protect the weld pool. The flux and gas prevent contamination during welding.

Unlike similar MIG welding, flux core does not require an external shielding gas. The self-shielding flux wire makes flux core a portable option. Flux core excels at welding thin materials by providing focused heat input. It offers versatility for home garage and fabrication shop use on metals under 1/4” thick.

Now that the basics of flux core welding are covered, let’s explore considerations when using it to weld floor pans specifically.

Using Flux Core Welding on Floor Pans

Floor pans provide the underlying support for a vehicle’s interior structure and components. To maintain vehicle safety and integrity, failed or rusted-out floor pans must be replaced with new solid metal sheet welded into place. Flux core welding is up to this task. Here are key guidelines when using flux core on floor pans:

Proper Machine Setup

With floor pan steel gauges ranging from 16 gauge to 22 gauge, it’s vital to have your flux core welder appropriately set up. Voltage too high or wire speed too fast risks burn through on such thin materials. Always reference your machine’s manual, but here are typical starting points:

  • Voltage (Volts): 16-18 V
  • Wire Speed (ipm): 250-325 ipm

Additionally, choose a smaller diameter 0.023” or 0.025” flux core wire. The smaller wire size concentrates heat input, preventing burning through thin floor pans. Use a contact tip sized accordingly for the wire.

Preparing Floor Pan Metal

Before attempting to weld floor pans into place, proper preparation is a must. Take time to completely clean and fit the new floor pans first. Remove any paint, rust, scale and grease from the area to be welded. Grind the welding surface to bright, clean metal. Any debris left in place will contaminate welds.

Dry fit the new floor pan and ensure proper fit-up prior to welding. Floor pans should fit flush with only a small gap between joints. Grind or file edges if needed to achieve a proper mating surface.

Recommended Technique – Spot Welding

Due to the thin gauge of floor pans, it’s not recommended to continuously weld the full seam in one pass. The concentrated heat input increases chances of burning through or warping the metal. Instead, utilize a spot welding technique:

  1. Make a series of small tack welds 1”-2” long with 1”-2” spacing between them along the seam.
  2. Allow time between each spot weld for the metal to cool and avoid overheating.
  3. Once the seam is tacked, go back and tie in each spot with a final weld.

Spot welding prevents warping and grants better control when welding floor pans. Take care to keep welds tight without undercutting or overlap.

Caution When Welding Galvanized Floor Pans

Some replacement floor pans feature a galvanized zinc coating for corrosion resistance. While flux core welding can be used on galvanized steel, extra caution must be taken for safety. Zinc vaporizes at high temperatures, releasing potentially toxic fumes. Proper ventilation, respirator use, and low amperage are critical. Consider removing the galvanized coating along weld seams for safer welding if possible.

Additional Flux Core Welding Tips

Beyond proper setup and technique, following general welding best practices will produce better results:

  • Maintain consistent wire stick-out of ~3/8” for even wire feed.
  • Use a slow travel speed and whip/weave technique to control heat input.
  • Keep a tight arc length, minimum spatter will ensure quality welds.
  • Make multiple weld passes on thicker floor pan areas if needed.
  • Allow ample cooling between passes to control warping.
  • Grind welds smoothly for professional looking final results.

FAQs – Welding Floor Pans with Flux Core

What problems can occur when flux core welding thin floor pans?

The main problems when flux core welding thin floor pans are burning through the metal, warping from excessive heat, and poor weld fusion due to surface contamination. Proper machine settings, cleaning, material fit-up, and using a controlled spot weld technique will overcome these issues.

Is MIG or flux core better for welding floor pans?

Either process can weld floor pans effectively. Flux core welding has the advantage of being self-shielding without requiring an external shielding gas. This makes it simpler to use portably. MIG may allow a little more heat control on thin materials when using smaller diameter wire.

Can you use flux core welding outdoors?

Yes, flux core welding can be done outdoors thanks to its self-shielding properties from the flux within the wire. There is no need for an external shielding gas that could be blown away by wind. It is best to avoid direct wind on the weld area by using a windscreen.

What amperage is recommended for welding 16 gauge floor pans with flux core?

For welding 16 gauge floor pans with flux core wire, a 75-80 amp range is usually suitable. Too much amperage risks burn through, while too little may not achieve full weld penetration. Take time to practice settings on scrap pieces of 16 gauge steel until the amperage is properly dialed in.

What size flux core wire should be used to weld floor pans?

For best results when welding thinner floor pan materials, use .023” or .025” diameter flux core wire. The smaller diameter keeps heat input focused. Larger wire sizes can be more difficult to prevent burn through on thin automotive sheet metal. Match wire size to tip size.

Can flux core weld through rust and paint?

It’s not recommended. For the strongest welds, remove all rust, scale, and paint from the areas to be welded by grinding the metal to clean, bare metal. Flux core welding can theoretically burn through surfaces contamination, but it risks porous, weak welds.

What welding rods work best for patching floor pans?

.023” or .025” diameter flux core welding wire will provide good results for welding patches into floor pans. Use AWS E71T-GS .030” diameter gas-shielded MIG wire for more delicate welding work on floor pans thinner than 20 gauge steel. Avoid thick, heavy coated stick electrodes.

What kind of welder is needed for floor pans?

A 120-volt flux core MIG welder with continuous voltage control provides the best versatility for floor pan welding. Smaller 110V welders allow for the fine heat tuning needed on thin automotive sheet metal. Ensure the machine has voltage control and accepts .023” or .025” diameter flux core wire.

What causes warping when welding floor pans?

Excessive concentrated heat is the primary cause of warping thin sheet metal floor pans when welding. To prevent warping, avoid overheating the material by using proper machine settings, moving quickly, allowing cooling between welds, and using a spot-weld technique. Proper panel fit-up and use of clamps also reduces warping risks.


Repairing or replacing a rusted or damaged vehicle floor pan is made much easier through use of flux core welding. While requiring care and practice on thin gauge sheet metal, flux core allows for quality full penetration welds without the need for shielding gas. Proper machine setup, metal preparation, welding technique, and flux core wire selection enable success when taking on automotive floor pan welding projects. With this knowledge, DIYers can keep restoration budgets low by welding floor pans themselves using their flux core MIG welder and prevent having to outsource the work.

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