How to fix a rusting floorboard in a car?

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ChatGPT said:
Fixing a rusting floor in a classic car requires careful assessment, cutting out damaged sections, and replacing or patching with new metal. Here’s a step-by-step guide:

Tools & Materials Needed:
Wire brush or angle grinder with a wire wheel
Rust converter or rust remover
Cutting tools (grinder with a cutoff wheel, air saw, or plasma cutter)
Sheet metal (matching thickness to the original floor)
Welding equipment (MIG or TIG welder)
Self-etching primer and automotive-grade paint
Seam sealer
Undercoating
Safety gear (gloves, goggles, respirator)
Step-by-Step Process:

1. Assess the Damage

Remove the carpet and insulation to expose the entire floor.
Use a screwdriver or pick to poke at suspect areas to determine if the metal is weak or completely rusted through.

2. Remove Surface Rust

Use a wire brush or grinder to remove loose rust.
Apply a rust converter on minor rust spots to stop corrosion from spreading.

3. Cut Out Rusted Sections

Mark the rusted areas to be removed.
Cut out the damaged sections using a grinder, air saw, or plasma cutter, ensuring you cut into solid metal.

4. Fabricate Replacement Panels

If using pre-made floor pans, trim them to fit.
For custom patches, use sheet metal and shape it to match the contours of the floor.

5. Weld in the New Panels

Tack weld the replacement piece in place to prevent warping.
Fully weld around the edges, using short bursts to control heat and prevent distortion.
Grind down welds smoothly for a clean finish.

6. Treat and Seal the Floor

Apply rust inhibitor on surrounding metal.
Coat the repaired area with self-etching primer.
Seal all seams with automotive seam sealer.

7. Paint and Protect

Paint the floor with rust-resistant paint.
Apply an undercoating on the underside of the car for added protection.
Reinstall carpet and insulation.
Tips for Longevity
Check for water leaks (from windshield, doors, or heater core) that might have caused the rust.
Consider installing sound deadening and moisture-resistant insulation.
Regularly inspect and touch up any exposed metal.