[Strassenkreuzer]

So my cutting and polishing exercise (never been done on my 28 year-old 300SE) made the car look tons better, but I think I made a rookie mistake and managed to cut a bit too deep at the edge of parts of the sunroof cutout—and there's now a bit of rust along parts of it.

I know it can't be deep--yet. Any suggestions on how to "seal off" the areas from further rust...or is the process more complicated? Ideally I'd like to just put something on it to prevent more rust, but I also know that removing the small amount of rust, and then sealing it, is probably the right thing to do. I just don't want to mess up the paint. I'm not opposed to "doing it right," but for now I need a stop-gap measure to prevent the rust from worsening.

Any suggestions are appreciated. Thanks!

 

[luckymike]

My opinion? Mask off to just outside the damaged area, prepare it and shoot it with some touch up paint and clear. The eye probably won't notice the line and you'll have protected paint.

 

[dadrab]

My opinion? Mask off to just outside the damaged area, prepare it and shoot it with some touch up paint and clear. The eye probably won't notice the line and you'll have protected paint.

This is your answer. Do it quickly before the rust spreads to metal under the good paint.

 

[alexstorm]

Touch up with spray causes some overspray issues that dull the shine of the surrounding paint. You can try afterwards to polish and smooth over the areas, but it will not be perfect. I like carefully sanding all the rust off, mask off everything plus 20 inches of car all around with newspapers, so you see only the rest, do an 3 very light undercoat sprays, letting it dry each spray, only on the rust parts. Then either spray or touch up to bring the color back.

In the end you should not be spraying any part of the outside car color that is not damaged. You will have the car protected. You will see a sharp line where the rust was, hopefully that will just be the inner edge. This way you don't get any overspray dulling. I think that looks a lot better.

Hope that helps.

 

[Strassenkreuzer]

My opinion? Mask off to just outside the damaged area, prepare it and shoot it with some touch up paint and clear. The eye probably won't notice the line and you'll have protected paint.

Thanks, Mike. When you and @alexstorm talk about "prepare it," I assume that to mean removing the rust. Is it true that simply sealing off the rust by putting lacquer or something on it doesn't prevent the rust underneath from spreading?

Alexstorm mentioned sanding, but is dissolving the rust better—using muriatic acid or some other product designed to do that? However, I'm worried about he surrounding paint. Does anyone know if using these "rust-eaters" also will chew up surrounding paint?

I get that I need to take care of the rust and then seal it; I'm just not sure which method is best suited to this rather dainty application along a very narrow strip of steel.

One other thing: By "touch-up paint," do you mean a spray color coat that matches the original paint spec? Where does one get such a thing? Or will simply removing the rust and then sealing it with a clear lacquer do the same thing—with the downside being that the bare metal will be visible in those narrow spots?

 

[luckymike]

Thanks, Mike. When you and @alexstorm talk about "prepare it," I assume that to mean removing the rust. Is it true that simply sealing off the rust by putting lacquer or something on it doesn't prevent the rust underneath from spreading?

Alexstorm mentioned sanding, but is dissolving the rust better—using muriatic acid or some other product designed to do that? However, I'm worried about he surrounding paint. Does anyone know if using these "rust-eaters" also will chew up surrounding paint?

I get that I need to take care of the rust and then seal it; I'm just not sure which method is best suited to this rather dainty application along a very narrow strip of steel.

One other thing: By "touch-up paint," do you mean a spray color coat that matches the original paint spec? Where does one get such a thing? Or will simply removing the rust and then sealing it with a clear lacquer do the same thing—with the downside being that the bare metal will be visible in those narrow spots?

Bear in mind, mine is the opinion of a non-professional hobbyist.

On my own car, I would try to carefully sand away the rust and then prime and paint. The masking tape should protect the paint you don't want to disturb.

Yes, I do mean spray paint that matches the original. I have found pretty good matches at the local parts store. For this tiny strip, close may be good enough. If not, I understand some paint places will sell you a customized can or you can order online. I don't have experience on that.

Finish off with clear. I would use multiple thin coats for all three steps.

PS. I wouldn't count on truly being able to 'seal' the rust by painting over it. If you don't want to or can't remove it all, I would definitely apply POR-15 or similar. I've read good things about the POR.

 

[dadrab]

POR 15 is very good stuff. I've restored several fuel tanks with their kits with no mishaps...yet.

For your purposes, I don't think you need that, but...BUT you cannot paint over rust. Sealing it up is one thing and can prevent further invasion, but in a spot such as you describe, I'd get rid of it.

As luckymike says, tape off everything you don't want scratched or altered. Make sure you tape paper in an area three times the size you think you'll need to. Spraying primer will go everywhere and get places you'll find later if you don't.

Begin with a fine emery board or two and get rid of that rust down to bare metal. Finish that with some 600 sand paper.

Prime the area.

Allow it to dry well and hit it with some 800 then 1000 paper.

Color coat and hit that with some 1000 paper before applying some clear.

 

[alexstorm]

Never even thought a rust eating liquid. I have always just sanded the rust completly away. Often you need various grades of sand paper. It's possible that the rust has eaten through the metal, in which case you use filler resin and sometimes mesh to plug the whole but stay below the line of the top metal, then you add putty filler with hardener, sand rough back again and add final fine fill and sand back again smooth. I may have done, maybe 30 cars. In all cases if you sand enough the rust is removed. All this technique is covered in many different books out there. If you have to start using putty, you really need a teacher to show you the method. It's nice, once you learn it, but it's not obvious.

I thought we were dealing with just a small line of rust that snad paper could handle, based on that photo. I have never used liquid rust removal. Watch out any spot of car metal you touch with sand paper is immediately marked. The only way back to perfection is pretty much paying a body shop or really learning the craft and having the correct spray tools, compressors and paint shed.

 

[Strassenkreuzer]

POR 15 is very good stuff. I've restored several fuel tanks with their kits with no mishaps...yet.

For your purposes, I don't think you need that, but...BUT you cannot paint over rust. Sealing it up is one thing and can prevent further invasion, but in a spot such as you describe, I'd get rid of it.

As luckymike says, tape off everything you don't want scratched or altered. Make sure you tape paper in an area three times the size you think you'll need to. Spraying primer will go everywhere and get places you'll find later if you don't.

Begin with a fine emery board or two and get rid of that rust down to bare metal. Finish that with some 600 sand paper.

Prime the area.

Allow it to dry well and hit it with some 800 then 1000 paper.

Color coat and hit that with some 1000 paper before applying some clear.

Thanks, @dadrab. This is the approach I think I'm going to take. I think the POR is going to be too much for this tiny area, and I don't want to risk messing up the rest of the roof.

 

[Strassenkreuzer]

I thought we were dealing with just a small line of rust that snad paper could handle, based on that photo. I have never used liquid rust removal. Watch out any spot of car metal you touch with sand paper is immediately marked. The only way back to perfection is pretty much paying a body shop or really learning the craft and having the correct spray tools, compressors and paint shed.

You're right, @alexstorm. Using a liquid rust remover is likely overkill in this case—when an emory board will likely remove the rust. While I'm at it I'm tempted to dismantle the whole sunroof and lubricate the mechanism and install a new rubber seal.

We'll see how ambitious I get. Right now, with summer on the way, my higher priority is to get all six of my HVAC vacuum pods replaced so I can fix the air distribution problem. I only wish I had a garage with a hydraulic lift, a complete set of tools, and a fatter wallet to make it all happen faster. On the plus side, working on these cars is a kind of therapy; it has the same relaxing quality about that I think my grandmother enjoyed whilst doing her knitting. :grin

Thanks for all the advice!