Originally Posted by Roadrunner
I used a bug sprayer to apply it. You can brush/roll it on if you want. It will not eat holes in the metal. It stops further rusting. Just put it on and when it dries it turns white. You may need a second coat. It kinda turns to powder when it dries. Use goggles/respirator. When it is dry sweep the powder up, prime/paint over the Ospho and lay some sheet metal over where the bad spots are. The easiest way to fasten the new sheets would be to use pop rivets. Do you know how to use them? You could tack weld them but I assume you are not a welder LOL. You won't need too many, just enough to keep it in place. You could reuse the ceiling panels if you are removing them. You can use any thickness of metal. I would not go super thin though. Go to a metal supplier and look at the different gauges. I would think 20 or 22 gauge would be good enough. Just make sure to clean the new metal good and apply primer/paint to protect it. It should outlast the rest of the bus. I would not worry about reinforcing it underneath the bus. Just overlap the edges of the bad spots a little bit. Please don't hesitate to ask questions. I know you will have tons of them. Good luck.
Most buses use 15/16 guage sheetmetal and even covering or repairing I would go with nothing less than original rotten metal? I like to use stainless steel rivets for metal to metal connections because the stainless is stronger than what you are attaching and can resist all the twisting and turning of the metal as it is going down the road.
When you look for sheetmetal if you want to paint it.
There is raw/non-galvanized that will soak up several coats that you have to ask for in the 18-26 guage sometimes the thicker 16-12 guage is available but not common in a workable dimension for the homeowner.
If you do end up with galvanized sheetmetal to paint (which i would use)you can see a coating/clear sheen on the metal that needs to be taken off before it will ever hold paint.
More time and money
Use vinegar to take the coating/sheen off and buy a self etching primer.
Going to the big box store they are going to sell you a cold galvanizing compound in a spray but the metal is already galvanized?
If you choose this option find a commercial paint supplier and they probably have/can make samples in quarts which will cover quite a bit as far as patches go.