Prepping the Bus Floor for Painting

Before you can paint the metal floor of a school bus, you have to do some serious prep work!  Get ready for this to take way longer than you ever imagined. The key to prepping the floor is removing and then converting rust.  Untackled rust on that floor can jeopardize your whole bus conversion, so this is really important.

Required Tools & Materials:
  • Angle grinder with metal brush attachment and sander attachment
  • Drill with a wire brush attachment.
  • Utility knife
  • A degreaser (we used Simple Green)
  • Cleaning supplies: bucket, rags, scrub brush
  • A rust converter (we used Ospho)
  • Access to a hose
  • Paint brushes
  • Safety glasses and a mask so you don’t breathe in that rust dust
  • Time.  Lots of time.
Step 1 – Initial Rust Removal

We were lucky that we only had surface rust.  If you have major holes, you should keep searching the net for help on how to handle those.  If they are really bad, you might even consider halting your conversion right now before you put more money into your bus.

  1. Remove as much rust as you can with the angle grinder.  Remember to wear a mask because that dust is nasty!
  2. Use the drill with wire brush attachment for tight spots or grooves you can’t reach with the angle grinder.
  3. If you are painting your lower wall panels like we did, do a pass over with the angle grinder + sander attachment to create a rougher surface.
Step 2 – Clean and Degrease the Floor
  1. Use a degreaser, the hose, and your mad dance skills to clean that floor!  Your aim is to get rid of all the rust dust, grease, and grime.
  2. Give the floor enough time to dry.  You want to end up with a bone dry floor.  Don’t be hasty now, Precious.
Step 3 – Second Pass of Rust Removal (Optional)

We went across the whole floor with a rust removal gel.  However, we feel this step ended up being a waste of time and money for us, because our remaining rust really was minimal and was easily taken care of by the rust converter.  It is entirely up to you whether you want to do this step.  If you do:

  1. Apply your rust remover and follow the product’s instructions for amount to apply/wait time.
  2. After it’s done its work, completely wash away the rust remover.
  3. Again…give the floor time to completely dry.  Argh..
Step 4 – Rust Conversion

Applying a rust converter has two key purposes.  First, is to convert any remaining rust into iron phosphate.  Second, if your floor is galvanized steel like ours was, the rust converter serves to also etch the floor.  This is necessary if you plan to use a Rustoleum primer like we did, as that primer will not adhere to galvanized steel.  The rust converter will etch the galvanized steel and make it compatible with Rustoleum primer.

  1. Apply a rust converter to the floor, following the product’s instructions!
  2. Tip:  We used Ospho and applied it WAY too thick.  After 72 hours it still hadn’t dried correctly!  This was partly because the humidity was so high, but also because we applied so much.  If you are using Ospho, a thin layer is all you need.  If you can leave the bus windows open to allow for air circulation, this will help it dry faster too.
  3. Rinse the floor thoroughly so that an acid film does not remain.  An acid film can result in your paint not sticking.  Which sucks.
  4. Wait till the floor is bone dry again.

Now, finally, you can start painting that floor!