Rust on the roof

Personally, I'm rather surprised it rusted. My 12 year old Explorer had many chips and scratches down to bare metal and it never rusted, even after 5 years in Pennsylvania where the streets turn white in the winter due to all the salt and brine they put down.

I figured that meant auto manufactures had figured out how to make sheet metal that didn't rust.

 

<div class='quotetop'>QUOTE(ScottY @ Nov 3 2006, 03:31 PM) [snapback]343434[/snapback]</div>

I wouldn't expect them to, but it might not hurt to ask. How big are the spots? I get a few stone chips, and I just touch them up with the ink-pen-like touch up paint thingy I got from the dealer. The hood, though, doesn't seem to rust. If they are small enough, I'd be tempted to hit them with a dab of rust killing paint, and then touch up. And by rust killing paint, I'm specifically thinking of something called "Extend" in the hardware store that comes in a plastic bottle. If they are bigger, find a body shop, you want to stop the rust before it does rust through. Good luck!

 

<div class='quotetop'>QUOTE(Beryl Octet @ Nov 3 2006, 04:41 PM) [snapback]343442[/snapback]</div>

Because the hood and hatch are aluminum.

 

<div class='quotetop'>QUOTE(Marlin @ Nov 3 2006, 03:43 PM) [snapback]343443[/snapback]</div>

Thanks, I actually thought they might be some sort of plastic.

 

<div class='quotetop'>QUOTE(ScottY @ Nov 3 2006, 03:57 PM) [snapback]343450[/snapback]</div>

If they are small enough, then the touch up paint alone should be just fine, I think. You basically want to prevent oxygen from getting to bare metal.

 

We have these rust spots on our '06 Prius as well. About four of them, that I've counted so far.

I just noticed them the other day, as I was washing the car, just like you.

I suspect that these rough feeling tiny dots of rust are actually the result of airborne inorganic iron particles, like brake dust or rail dust or some other byproduct of transportation friction, that landed "hot" on the roof surface and micro-melted/softened the paint film long enough to embed themselves... most likely just into the clear coat (if the Prius is two stage... hopefully it is).

So what is most likely actually rusting is the inorganic particle itself, and the rust spot gradually appears to grow larger as the iron particle "expands" from the corrosion sluffing itself. In other vehicles, there is enough paint mil thickness in the base coat to separate this rusting particle from the roof panel itself, so I would guess that the roof is not what is actually rusting, only the particle.

I don't know how thick the paint is on the Prius, but I'm becoming less and less enchanted with this car every day I learn something new about it.

Removal of the embedded iron partical is very difficult with normal washing. It takes more extreme methods. The least invasive of these methods is extremely time consuming... using clean clay bars with a lubricant. Less time consuming, but extremely scary is by treating the finish with an oxalic acid solution combined with water and a non-alkaline detergent. This is the method that domestic manufacturers recommend that dealers use to address consumer complaints similar to ours. Domestic vehicles are transported around the country by railway, and the steel train wheel to rail makes for a lot of hot rail dust enroute.

There are a lot of detailing websites that discuss clay bars. It's harder to find information on the oxalic acid wash, which is too bad, as there are definite cautions to be adhered to, not the least of which is a thorough rinse with clean water!

The most extreme method of all is color sanding with micro fine 1500 grit or greater automotive finish paper. This method WILL remove paint mil thickness, which WILL cause the paint to fade and degrade sooner than the areas of the car that still have the full thickness of clear coat intact.

Prior to colorsanding, I would first try an wax and grease remover. I know from experience that PPG Acyliclean DX330 is paint safe. There are other similar products like Dupont 2930. The 3M wax and grease remover is more readily available in consumer automotive stores, but it leaves an oily residue, whereas DX330 evaporates right away. Yep, right into the environment, so there is a conundrum for the Prius owner as well.

If clay bars don't work, and the oxalic acid wash solution was too hard to come by, then you can try a a mild buffing compound. Rather than using a rotary automotive buffer, you might try using a dual action random orbit style buffer. Meguiar's car wax company sells one, it's basically a re branded Porter Cable angle drive random orbit sander fitted with buffing sponges/pads instead of a sanding pad.

I don't know what I'm going to do about my newly discovered rust spots yet. My Prius has been at the dealer for the last three days and counting...