How do I prevent rust where I cut and weld?

Documented on the Ford Mustang build

Published February 26, 2026

Clean and prime all bare metal immediately, use an epoxy or self-etch primer, seam sealer on joints, and consider an undercoating or bedliner in the wheel well.

Full Answer

Clean and prime all bare metal immediately, use an epoxy or self-etch primer, seam sealer on joints, and consider an undercoating or bedliner in the wheel well. Regular inspections and touch-ups will extend longevity.

Documented In This Build

From cuts to custom fender wells on my Mustang Pt 4 Ford Mustang

Related Knowledge

How much extra clearance will custom fender wells give me?What materials and thickness should I use for the tubs?Do I need to weld the tubs in or can I use rivets?Will cutting the inner fender affect structural integrity?How do I prevent warping when welding thin sheet metal?What wheel/tire sizes can this modification accommodate?How much extra tire/wheel clearance can I expect?How difficult is this for someone with limited metalworking experience?

Related Parts

Seam sealer

$12

MIG welding wire

$15

Primer (self-etch or epoxy)

$30

18 gauge mild steel sheet (or equivalent sheetmetal)

$60

Pop rivets / rivet nuts

$10

Wheel tub / inner fender panel (replacement or prefabricated kit option)

$120

Shielding gas (MIG mix)

$30

Body filler (Bondo) / finishing materials

$15

Topcoat / bedliner / underbody coating

$60

Rust inhibitor / etch primer (optional)

$20

Related Tools

Jack and jack stands

MIG welder

Clamps (sheet metal clamps / C-clamps)

Angle grinder with cutoff wheel and flap disc

Electric or air drill (with hole saws / spot weld cutter)

Metal snips / aviation shears

Metal hammer and dolly set

Measuring tools (tape, straightedge, scribe)

Rivet gun / rivet nut tool (optional)

How do I prevent rust where I cut and weld?

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