Originally Posted by BRAGeorgia
The bottom of the bus does have a good bit of rust. I plan on getting a few guys with wire brushes to scrape the underside pretty good, then apply POR-15 which should prevent/slow down the process. That POR is meant to be put right over the rust (Paint over rust) and create a hard shell. Frame and everything is still in good shape with lots of metal left!
You can see below from the picture of the new air tank I installed the amount of rust.
View image: 20150914 155226
Por 15 Will not paint over rust
. It will just fall off in no time at all.
The por 15 system is composed of 3 chemicals. De greaser, rust converter, and the paint.
The more rust, the more converter it takes. I'm talking gallons of the stuff. To make matters worse, it will not penetrate the rust on the bottom of the bus due to gravity. It will simply drip off and only wet the outside layer of rust.
To convert something as rusty as the bottom of a bus, you would need to drive it into a bath of the converter chemical, and soak for a week. The longer you keep it wet, the better job it will do.
Also don't spray the rust converter chemical it hot dry weather. It will simply evaporate, and do nothing. I had the best converting of the rust when I sprayed it on in the evening just before dark. The night time dew would keep it moist till morning, and I saw great conversion of the rust.
The only time por 15 can be painted directly over rust is when it is fresh surface rust with no scale.
So basically it is a marketing farce.
Now oshpo is 10 times the product as the por 15 rust converter, but all the same things still apply. It needs to stay wet as long as possible.
If I was to paint the underside of a rusty bus, I would sandblast it lightly before rust converting.
All information I have posted here is based off experience with the products listed.