I pulled up the floor, and there is some pretty significant scale rust under there, but the few small holes were pin-sized to just over a half-dollar size here and there. Nothing around the wheel wells. Still a bit disheartening, since we paid a bit more for a clean "Texas" bus that only had a tiny speck of rust under the license plate when we looked her over. I think that the school district from where we purchased it just pressure-washed the floors periodically to keep the dirt and kid-gunk down. Washing from front to back, letting it all drain out the back door. They assumed, incorrectly, that the rubber mats would keep the wet off the steel. When we pulled one of the plywood sheets up, it was still damp underneath, and I bought the bus around the 7th of April. So, boo, hiss, and oh, well. I spent today figuring out what method would work best to get the rust off. I started with the cupped wire brush and angle grinder, but that really only flaked off some of the layers, and polished the rest. If you whacked it with a hammer, the shiny pretty stuff still flaked off. The next step was to take the grinder disk, one a little thicker than the one I used to cut off the bolts, and sort of scraped off the flaky layers to get down to the pitted metal. Long work. I managed (doing this almost all day) to do about 8 square feet. Only 116 more to go I reckon. My question to the forum is this: How far down should I go? Just past the flaky layers? If I were to put rust converter on top of flaky layers, wouldn't I just have converted flakes? We are doing this on a friends new driveway, so I hesitate to use any converters that have to be rinsed off.