Rust Repair on a School Bus: A Skoolie's Guide to Fixing Lower Side Panels, Dog Houses, and Wheel Wells
Custom Bus and Truck Panels · 2026-06-10
You pulled the interior paneling and found the rot. Here's how to decide between a patch and a full panel, the tools you really need, and where to source the parts.
Every skoolie build hits the same moment. You're pulling interior panels or cutting out the old floor, and there it is. Sometimes it's a little bubble. Sometimes it's a hole the size of a softball that you could put your fist through. Either way you're at a fork, and picking wrong costs you money if you over-build it or time if you patch it badly and redo it in two years.
The three places the rust actually is
After watching hundreds of conversions come through the shop, almost all the rust you'll deal with lives in three spots. Worst first:
- Lower side panels, from the bottom of the windows down to the floor edge. This is ground zero. Salt, mud, and gravel all collect here.
- Wheel wells, both the outer lip and the inner fender hiding behind it.
- Dog houses and the firewall, where engine heat and moisture speed everything up.
We'll take them one at a time, with a simple rule for patch versus replace.
Zone 1: lower side panels
These are thin sheet steel, usually somewhere in the 18 to 20 gauge range. The factory panels have a return lip top and bottom, and they're held to the body posts with screws and structural adhesive. Rust starts at the bottom lip where water sits, then creeps up.
Patch it when
- The bad spot is smaller than a softball and it's the only one
- You've got a welder and the time to cut, fit, and weld
- The metal around it is solid and doesn't flex when you push on it
Replace the whole panel when
- Rust runs more than two feet along the bottom edge
- There are several soft spots on the same panel
- The panel is creased from a hit, because rust gets down in the fold and you'll never fully clean it
- You don't weld, and a structural panel is not where you want to learn
The three-foot rule
If rust covers more than about three feet of one panel, replace the panel. Patching that much takes longer than swapping it, and you're welding new steel into tired old metal, so the repair comes out weaker than a fresh panel.
Zone 2: wheel wells
Wheel wells are a stamped shape with a flange wrapping the opening, so a clean patch is hard. The usual move is to cut out the rotted section, the lip plus four to six inches around it, and weld in a repair panel. We stock those for Blue Bird, Thomas FS65 and C2, International, and most of the common buses.
Cutting it
Mark your cut at least two inches past the rust you can see. The visible rust is the tip of it, and the metal around it is thinner than it looks. Cut with a plasma torch or a thin cutoff wheel, grind the edge to bright steel, and dry-fit the panel before you ever strike an arc.
Don't skip the inner fender
When the outer well comes out, look at the inner fender behind it. It's almost always worse. Most builders do both at once, because reaching the inner one later means cutting your fresh outer well back out.
Zone 3: dog houses and the firewall
Dog houses are the engine covers inside the bus. They're thin sheet steel, and they take a beating from heat and vibration. A dozen screws and they're out in a few minutes. When one is rusty it's almost always easier to swap the whole thing than to patch it, because the shape is too fiddly for a clean repair.
The firewall is a different animal. It's structural, usually heavier steel, and patches on it are normal and fine. Just watch what's on the other side first. Brake lines, fuel lines, and wiring all live back there. Throw a fire blanket over them before you weld.
The tools you actually need
Not a quick tack job. A real repair:
- A plasma cutter, or thin cutoff wheels for a grinder
- A MIG welder, 140 amp at a minimum, 200 is better for the thicker steel
- A good auto-darkening helmet (buy the decent one, your eyes will thank you)
- An angle grinder with flap discs and cutoff wheels
- A wire wheel for cleaning the parent metal
- Hammer, dolly, and a shrinking disc for shaping patches
- Rust converter for any metal you're leaving in place
- A weldable primer if you plan to weld over it
Where to get the panels
For the common buses we stock panels in standard sizes. The part number is usually stamped or stickered on the back of the original, so check there first. If you can read it, look it up and order the match.
If the number rusted off, measure the panel and send photos from three angles. We'll match it to a stock panel or bend one to suit, and we ship from Ohio.
Need a panel for your bus?
Send the part number, the year, make, and model, and three photos. We'll quote the stock panel or a custom bend.