Painting fender rust - what did I do wrong?

[Spidey]

I had a small patch of rust on my 2006 F250 that I ground down to bare shiny metal and I put 3 coats of auto primer and 3 coats of color on (this was back in the summer). The color match worked really well but over the next couple months the rust started up again and now it's back to where it was.

Should I have put some sort of treatment on metal before the primer? I used CDN Tire primer - so maybe that was it?

All advice is most welcome. That truck has been awesome to me so I want to keep it looking nice as long as possible.

[TylerThomson]

Did you do both sides of the panel? If you have access to a mig machine you can buy a small roll of automotive wire and cut a patch in.

[Spidey]

Originally Posted by TylerThomson

Did you do both sides of the panel? If you have access to a mig machine you can buy a small roll of automotive wire and cut a patch in.

No, I didn't as it appeared to only be surface rust. It came off easily and the exposed metal looked good (couple small grooves where the rust was but still solid). I took off an extra couple inches around the rust patch to make sure I got all the rust. That said, I will take a closer look on the inside panel. Thanks.

[Sooner]

As a ex body man, grinding never gets all the rust out. Sand blast is better but it can warp the metal. Friends swear by the stuff that changes the rust's composition(can't remember the name) but I never seen it work in the shop.

Once you have it, it's always coming back unless you replace the panel. Assuming its on a wheel well, buy those fender flares & live with it

Other issue is CT stuff is not quality stuff. Stop in at a Napa store and buy some good etching primers and use that if you can guarantee the rust is gone.

[Trochu]

You'll need to apply a metal etch/prep, CT sells Por-15 which is pretty good stuff, isn't it?, prior to priming or use an etching primer.

[Grizzly Adams]

Interesting. Got a rust spot on the lower box, just behind the cab, on my Ford. Headed for the fourth go around. Tried wire brushing, sanding, even sand blasting, followed by one of those metal prep primers. Couple of weeks and the rust starts showing through again.Must be cause it's a Ford.

Grizz

[Spidey]

Originally Posted by Sooner

As a ex body man, grinding never gets all the rust out. Sand blast is better but it can warp the metal. Friends swear by the stuff that changes the rust's composition(can't remember the name) but I never seen it work in the shop.

Once you have it, it's always coming back unless you replace the panel. Assuming its on a wheel well, buy those fender flares & live with it

Other issue is CT stuff is not quality stuff. Stop in at a Napa store and buy some good etching primers and use that if you can guarantee the rust is gone.

THanks for the tip on the etching primer. I'll give that a shot and if that doesn't work I've already been pricing out fender flares!

[Dark]

Originally Posted by Grizzly Adams

Interesting. Got a rust spot on the lower box, just behind the cab, on my Ford. Headed for the fourth go around. Tried wire brushing, sanding, even sand blasting, followed by one of those metal prep primers. Couple of weeks and the rust starts showing through again.Must be cause it's a Ford.

Grizz

Same results as my attempts with my 06 ford

[Drewski Canuck]

Rust Converter, let dry, Zinc rich primer, then do rocker guard like all the shops do, and paint to match.

Drewski

[Spidey]

Originally Posted by Drewski Canuck

Rust Converter, let dry, Zinc rich primer, then do rocker guard like all the shops do, and paint to match.

Drewski

That's a really good suggestion as well. I did that back in the day on a GMC Jimmy and it looked pretty good!

[Arty]

Originally Posted by Trochu

You'll need to apply a metal etch/prep, CT sells Por-15 which is pretty good stuff, isn't it?, prior to priming or use an etching primer.

That works. (So does a deep sand blasting followed by a good primer and industrial coating system) http://www.endura.ca/

The POR-15 is really a 3-stage system involving essentially a surfactant (dish detergent) then rinse and dry, then dilute phosphoric acid (principle ingredient in 'anti-rust' gels) then rinse and dry, then a urethane paint. Don't let the first 2 stages dry out at all, until each is thoroughly rinsed off.

I've had great results in both cases, after rust sanding and painting many times for several years never worked. You have to stabilize and convert the rust (with the p-acid) and use a super-sealing epoxy/urethane such that there's no way moisture or water vapor can get through to the steel.

[TylerThomson]

I had never heard of rust converters. This is going to come in handy as i rebuild the body on my suzuki samurai. Thanks

[RZR]

Glass bead the area then use an epoxy primer.

[Drewski Canuck]

Tyler Thompson,

The product is called "Rust Converter". Key is sand well to get the loose stuff.

Then the Rust Converter, so you get the microscopic rust. Then the Zinc rich primer, which prevents rust through sacrificial anodization.

Then urethane ( rocker guard spray). Then paint. Tape off a nice line for a finished look, spray paint, leave for a week to cure. spray again. Then buff with polishing compound to blend to existing paint.

Youi may have to then do a clear coat and wait a week and again buff with polishing compound to smooth.

Suzuki Samari's are one tough little buggy!!!

Drewski

[TylerThomson]

Thank you for the run down. This will be a game changer

[10aciousB]

I had the same issue after a hit-and-run about 10 years ago. Someone ran an advanced turn light and left a nice palm-sized dent in my front fender and cracked the paint down to the metal. I had a family member pull out the dent, but by the time I got around to painting, rust had already set in. Did everything right, ground it down until the metal was polished with no visible rust, primer, base coat, clear coat, buffed it to a showroom shine, and within months there were signs the rust was coming back. Ended up trading it in before I lost all resale.

Unfortunately once rust is there, it's there for good. All you can do is slow it down or make it look good for a while, but in the end, it always comes back. There's a reason it's called truck cancer.

[jstubbs]

Probably rusting from the inside, despite what you think.

[colroggal]

Coca-Cola and SOS pads.

Colin

[gunluvr]

More than likely coming from the inside. Dirt gets trapped between inner and outer panels and never dries out. Also zinc-rich epoxy primers prevent corrosion better than anything else but will only work after you eliminate the source.
As a precautionary measure you can also add a redundant ground wire (fender-to-frame) to reduce electrolytic corrosion.

[Suzukisam]

You used ordinary primer. Not right. You must use a metal etching primer first where ever bare metals shows. Then do all your work on top of that. Ordinary primer does not seal the metal. If your doing touch up do not sand through the own primer if you do you must use etching primer or it will rust there. No other choice unless you want to try invent the wheel

[Joe Black]

Third time now.

Rusting from inside out.

You probably don't want to hear that as the inside may not be easily accessible. If it is, get at it, remove all rust and seal it. If not, anything you do will eventually fail.

[Bushrat]

Originally Posted by Joe Black

Third time now.

Rusting from inside out.

You probably don't want to hear that as the inside may not be easily accessible. If it is, get at it, remove all rust and seal it. If not, anything you do will eventually fail.

Always thought it was funny how 90% of what people call 'surface rust' is coming through from the backside of the panel. Usually that rust blister is pretty much the tip of the iceberg.

[SlightlyDistracting]

Im a journeyman auto body tech
You will not stop the rust. Period
Aside from cutting out and sectioning a piece you are putting a bandaid on an axe wound. You will not stop it

[Reeves1]

Car is getting 100% blast before POR 15 coating
Bad rust cut out & replaced with new metal first...

[Sooner]

Originally Posted by SlightlyDistracting

Im a journeyman auto body tech
You will not stop the rust. Period
Aside from cutting out and sectioning a piece you are putting a bandaid on an axe wound. You will not stop it

100%, only way to stop it is a new panel and new inner panels. We would cringe when a customer would come in and say "patch" that spot. Boss would advise against the quick fix that won't last. Nope, do it my way they would say.

So we would cut out that blistered section by about 2 inches from the spot and then the boss would call the owner back down and show him that piece of metal and all the surface rust on the inside. Some got the demo, some not and just did the patch. That blister you see is just the scout lol. All his friends are in behind waiting to join join him on the outside.

[Spidey]

Thanks guys. Had a look on the inside and sure enough - there is some rust, but still relatively solid. I'll clean/blast both sides this time and treat/condition accordingly. Then, depending on what it looks like cleaned up, I'll go with rocker guard process or fender flares.