Rust removal with Ospho
Ospho is a phosphoric acid-based rust removal and preventative that has some advantages over other rust removal methods: it's easy, inexpensive, and not particularly messy. This article demonstrates how to use Ospho to remove light surface rust and heavy rust, and how to use Ospho to prevent fresh steel from rusting.
 Tools and supplies
- A quart of Ospho.
- Red scuff pads, part #07747.
- Rubber gloves.
- Paper shop towels.
 Removing surface rust
Use a pump spray bottle to apply Ospho liberally. Scrub it in with the scrub pads, then wipe off the excess with the towels, and let it sit 24 hours. If you want to clean it some more, sand it with 80 grit, and reapply.
 Protect metal from rusting
If you strip an entire vehicle at once, but are going to be working on one panel at a time, you can Ospho the entire vehicle to prevent it from rusting. When Ospho dries, it leaves a protective primer coat that will prevent rust for months.
If there's excess Ospho on the steel, you may notice some streaking. To handle this, you can reapply the Ospho, and wipe it off smoothly.
 Prepping metal for Ospho
Sand with 80 grit, then clean with wax and grease remover.
 Prepping Ospho for primer
On exposed surfaces, sand the coating to give the epoxy primer something to bite into. If there was any streaking, you can sand a little more on those spots.
Sand with 180 on a DA, when wipe off the grayish powder with wax and grease remover, then prime.
- Using Ospho to clean/etch unrusted metal
- Removing surface rust with Ospho, part 1
- Removing surface rust with Ospho, part 2
- Prepping Ospho for epoxy primer
The use of acid metal pretreatments is controversial in hotrodding. Because incomplete removal of the acid film may cause topcoat failure, its use is explicitly cautioned against by some epoxy primer manufacturers.
For more details, see: Phosphoric acid as metal pretreatment.
 Related articles
- Adapted from a Hotrodders Bulletin Board forum post by deadbodyman, with permission.