How to fix roof rust

How best to fix this. I have the silver paint pen and I also have POR 15 from my frame. Any advice on stopping the rust creep.

 

i have that too, i would like to know as well

 

It's under the paint so the short, ugly answer is to grind/sand off your paint down to clean metal to treat the affected area. This means possibly welding pin holes shut up to cutting out and adding patch panels. You can tell by the way the rust is pushing the paint up as opposed to it peeling away from say a scratch or other damage. Rust is like cancer for metal. If you don't get rid of it all, it will come back and continue to eat away at your truck. To do it right, would mean to strip the affected areas (possibly the entire roof since there could be more hiding that hasn't reached the surface yet) and use automotive paint/primer to finish it off.
I know this is probably not what you want to hear, but it's the only way to do it correctly

That being said, a quick cheap ugly way to "control" it (because you won't stop it completely this way), would be to scrape away the paint that is bubbling up and use a rust converter like naval jelly to treat the area then you can use your paint pen to finish it off. You'll be able to tell that a repair has been made, but you'll at least slow the rust from spreading. Rust converters do not like to be applied over clean sheet metal so if you plan to use something like that leave a little surface rust so it can work properly as opposed to trying to sand it all off.
I personally wouldn't use POR15 on body panels, because it would leave brush strokes/application lines (if you're good, you can get it as smooth as house paint, but still not body-panel quality smooth). Try to use aerosols for your repairs/touch ups if you have them available and mask off areas that you will not be touching.

 

I had quite a few similar spots like this on my roof when I bought it. Of course, the best way to really fix the problem would be to sand, prime, and repaint the entire roof, but I'm on a budget, so I went for the cheaper fix. For the smaller spots of rust, like yours, I used a dremel with a metal bit to grind away all of the bubbling area and all of the rust under the paint.

Note: The rust will likely not be very deep into the metal, but it will have a larger surface area than the spot that is bubbling. For example, if you have a bubbling spot with a diameter of 1/4", then the rust has likely spread underneath the paint in a spot around the bubbling with a diameter of maybe 3/4". You will be able to see this when you grind the paint away.

I ended up grinding away enough paint and metal, in incrementally larger and larger circles, until all of the rust was gone. Be careful if you have rust spots right near the windshield seal - you'll probably need to pry up the edge of the rubber seal to properly get to all of the rust. I didn't use any rust reformer/rust converter, because I was confident that I had ground away all of the rust, and, as stated above, the rust converter doesn't really work well on bare metal.

Four spots that were ready for painting, one that I hadn't touched yet.


You'll want to wear a dust mask, because there will be metal and paint particles everywhere.


I used touch-up paint to then paint over the spots of bare metal, and gave them a generous coating of clearcoat to help protect them. Here is the finished product: not pretty, but I hardly notice them ever since they are on my roof and my truck is black. I could have used bondo or body filler of some sort to make everything even again, but it wasn't worth the time/effort to me, as the spots, surprisingly, are hardly noticeable.

Finished product

 

Looks good, definitely going to go the dremell route.

 

Any sanding tool will work, you just need to make sure you get all of the rust off, filler, sand, primer, sand, done. beer.

Important thing here is to protect the metal from more rust.

 

I did body work for about 10 years. Decades ago. On collector's cars as well as Jags, Porches, Roll's Royce and lots of Vette's. I never worked at a "stealership" except once and they fired me for not hashing out the paint work fast enough. They would even paint over grease at that "stealership". Not much has changed and the products I mention here may not even be available where you live due to the idiotic environmental restrictions these days. Sand it down and as someone already pointed out the rust will be more extensive once you start sanding. Get ALL the rust off that you can with sanding or even a dremel tool for the pits but don't go crazy. Find a product called "Rust Mort" which is still sold as far as I know. Naval Jelly is a joke. Follow the directions on the "Rust Mort" bottle to a "T". The stuff is a rust converter and works well. Then, get you're hands on a couple of quarts of PPG DP40. It's pricey because it's so good. It comes in various colors. Just get the standard "greenish" color. Follow the directions to a "T" as far as mixing it. It is a catalyzed epoxy sealer. Once it dries you can hit it with a hammer and it won't chip. I actually tried that. You can then apply a high quality plastic filler over it or catalyzed spot putty and sand smooth to make up for the thickness of the paint film. You can apply anything over DP40 as long as you follow the directions to a "T". Then you prime, sand, prime sand if you want it to look good and then paint it. I'm not going into how to make it look perfect. I'd be here all night.

As far as how good the DP40 is? I wanted to "detail" the engine compartment on the '73 Cadillac I bought back around 1992 and owned until 2016 as my only car. I used the black version of DP40 which has a different number like DP48 or something. The battery tray in that Caddy was very rusty. All I did was degrease the entire engine compartment with Simple Green or something like it, then hosed it down with a pressure washer and after it dried out for a few days I sprayed black DP in there. I didn't sand anything or do any other prep work besides that. I never treated that rust with anything on that battery tray and when I gave the car away in 2016 there was no rust bubbling up and no peeling. DP was originally made for use on Aircraft and, if it is still made the same way today? It rocks as the best sealer on the market.

Sand, grind down the rust as best you can then kill the rust with Rust Mort and then cover with DP and you're good to go. Wear a respirator when mixing or spraying DP. It's potent and quite bad for your health to breath whether it's the vapors or the mist from spraying. You can brush it on if you don't care about aesthetics but brush it on "thin".