Fixing a rust spot

[Jeepguy03]

Yesterday I noticed a rust spot on the roof of my XJ. The Jeep has 143k miles, and the rest of the body is spotless. I'm guessing there was a rust bubble here, and the paint flaked off a few days ago, because it wasn't there a month ago.

Here are some pics:

How should I go about fixing this? I'm a college student, so unless its absolutely necessary I'd like to avoid a body shop. It is on the roof so I'm not too concerned about looks, I'd rather just get rid of the rust and prevent it from coming back. My dad said to sand it down (I have a dremel with sanding disk), use primer, and then paint it. I do have a can of factory matching paint I could use, as well as a can of clear coat. Any suggestions? How should I prep? What kind of primer should I use? I've painted things before, but they were mostly lawn equipment with crappy paint to begin with.

Thanks for any help!

 

[tjmotter]

You will need:

1) 80 and 320 grit sandpaper (home depot)
2) potentially a dremel (home depot)
3) possibly some rust remover (Autozone or O'Reilly's)

First, you need to sand every bit of that rust off until you are down to bare metal. Use the dremel if necessary (but this may gouge) and you can cover any little bit left with some rust remover. Any inkling of rust left will just reappear so this is very important.

I find the best results with the rust remover is when you leave it on for a couple of hours and wipe it off with water. After this, you will need to neutralize the remaining acid by wiping it with a wet cloth and letting it dry fully (1 hr).

Next, you can't just use any primer over bare metal, you will need to either find a good epoxy primer (best option) or a good metal etching primer. Epoxy primer is a pro product so you won't find it in a spray can but you can get metal etching primer from any auto store. Metal etching primers have a little bit of acid in them so they "etch" into the metal to bond. They work pretty well for a small area but I wouldn't recommend them for a big area.

Before applying the metal etch primer you may choose to use some body filler to fix any gouges but if you don't care about looks, this is optional. It's actually pretty easy to fill a small area and then sand it flat (320 grit sandpaper) for a nicer looking finish.

Read the instructions on the metal etch primer looking for the "coat window" or "re-coat window". Let it sit for this time and then put a second coat on.

I typically let this sit overnight to cure and the next day, lightly sand the area with 320 grit again. Now you can apply a normal primer (I would go with grey since your car is silver) and after 30 minutes, spray the color. Let that sit for another 30 minutes and spray over it with some clear coat.


Note that before applying the primer or the paint or the clear, you should wipe the area with a wax and grease remover and then when that dry's (a couple of minutes), wipe the area again with a tack cloth.

HTH
Todd

Yesterday I noticed a rust spot on the roof of my XJ. The Jeep has 143k miles, and the rest of the body is spotless. I'm guessing there was a rust bubble here, and the paint flaked off a few days ago, because it wasn't there a month ago.

Here are some pics:

How should I go about fixing this? I'm a college student, so unless its absolutely necessary I'd like to avoid a body shop. It is on the roof so I'm not too concerned about looks, I'd rather just get rid of the rust and prevent it from coming back. My dad said to sand it down (I have a dremel with sanding disk), use primer, and then paint it. I do have a can of factory matching paint I could use, as well as a can of clear coat. Any suggestions? How should I prep? What kind of primer should I use? I've painted things before, but they were mostly lawn equipment with crappy paint to begin with.

Thanks for any help!

 

[tjmotter]

I should add that you only use the metal etching primer over the bare metal (or body filler). On top of that you will put normal primer to seal the area and prevent the metal etch primer bleeding through your paint.

The recoat windows are pretty important because you are aiming for a strong mechanical bond with the metal etch primer to the steel. The recoat window is the time specified by the manufacturer for the duration that the first coat is still wet enough to create a chemical bond with the second layer.

This is why you need to lightly sand the metal etch primer the next day so that you can get a good mechanical bond between the normal primer and the metal etch primer. The regular primer will also fill in most of the 320 grit sanding marks.

Once the regular primer has reached the recoat window, you can apply the base coat. The primer will still be wet enough to form a chemical bond for good adhesion. Same thing with the clear coat.

HTH

 

[Jeepguy03]

Thanks very much for the helpful info! As far as the metal etching primer, is this the "self-etching" gray primer they sell in the auto parts stores or is that different and there is a specific metal etching primer?

 

[MrAnderson]

:yelclap:now THAT is a response!:yelclap:

 

[8Mud]

Hammerite, http://www.hammerite.co.uk/products/index.jsp

Knock the loose stuff off with a wire wheel, paint it with Hammerite and forget about for 3-5 years (maybe longer).

 

[tjmotter]

Yes, this is the "self-etching" stuff in the autoparts store. It is available in a variety of colors but grey would be best based on your current color. You can also buy this stuff from companies like "Eastwood" but I find that the autoparts store stuff works fine for a small repair like this.

For larger areas you would want to use an Epoxy primer like the stuff on this page:

http://www.southernpolyurethanes.com/Pricing Info.htm

Epoxy is THE BEST for adhesion and corrosion protection but you need a spray gun and it is kind of expensive for a small repair like this. Plus it HATES any acid residue from rust remover so you have to prep more carefully.

Sorry for the long winded answer but I am in the middle of restoring a '90 Cherokee at the moment and figured much of this stuff out through trial and error. Initially I used an etch primer because I was stripping to bare metal in stages and didn't want the area to rust when I moved to the next panel. The problem was that while the etch primer stuck really good in some areas, it flaked off in others so I ended up sanding it all back down and covering it in epoxy primer.

This is why I am recommending that you leave the etch primer on over night to dry. This way you can easily tell if it has stuck to the metal. If it flakes at all, sand it down with 80 grit again and reapply. Do this until you get solid adhesion.

HTH
Todd

Thanks very much for the helpful info! As far as the metal etching primer, is this the "self-etching" gray primer they sell in the auto parts stores or is that different and there is a specific metal etching primer?

 

[tjmotter]

AkzoNobel makes good stuff but any rust encapsulator is simply a bandaid since they don't treat the rust, the simply cover it to starve it of oxygen. The problem with XJ's is that neither Chrysler nor AMC have ever been very good at properly prepping the body for paint and every one of them will have a thousand spider cracks with rust in them under the surface of the paint. This means that you can never fully encapsulate the rust because air will squeeze in through those cracks and your encapsulator will shred off over time. You are correct that you "could" get 3-4 years out of it but if you fix it properly, it will last a lot longer and be cheaper in the long run.

Hammerite, http://www.hammerite.co.uk/products/index.jsp

Knock the loose stuff off with a wire wheel, paint it with Hammerite and forget about for 3-5 years (maybe longer).

 

[tjmotter]

I should add that I used a rust encapsulator like this (POR15) on my first XJ. After 3 years all the rust came back and the repair was MUCH harder....

Doing it right will save you in the long run.

 

[Jeepguy03]

Thanks tjmotter for all of the great helpful info! I plan on tackling the rust spot this weekend after I'm done with final exams.

Have any pictures of your progress on the 1990 XJ restoration? My first vehicle was a 1990 XJ Limited that I miss dearly. I'd like to find an older XJ to restore someday, and learning about paint and body work like this is very helpful.


Edit: I have some POR 15 and the prep stuff that comes with it. I believe it is a chemical called "metal prep". I don't plan on using the POR 15 on the roof, since I'd like to fix it right. Would this be okay to paint over non-rusty areas such as underneath the Jeep? I was planning on painting the underside of my Jeep with POR 15 this summer to help prevent rust.

 

[tjmotter]

POR 15 is a really good protectant and I recommend it for under carriage spots (like the seam between the floor and the rocker panel) but I don't use it for rust encapsulation anymore, simply as a rock hard coating on an existing panel.

Here are a couple of picks of the XJ. I painted the door jamb's and the insides of the doors. Next step is to mount everything back on the beast, block sand the exterior panels and then spray the outside. I was lucky in that it only had a little bit of rust. There was a small hole in the drivers area, another where the transfer case linkage sits and another on the right rear quarter panel. For the quarter panel, I had to cut a hole about 2" x 4" to get to good steel. I was able to weld new metal in all areas and they finished off really nicely. I had some issues on the roof as well but they hadn't rusted through yet so I was able to save them.

 

[Jeepguy03]

Thanks for the pics, that looks great! Do you have a build thread here about the progress?