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Paint prep - dealing with surface rust.


Wood and Steel

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Hi all, 

 

I was trying to get my '51 Plymouth ready for paint last summer, but time got away from me. I left her out uncovered all winter like an idiot, so now I have even more work. ?

 

I'm having a hard time getting rid of the surface rust, especially on the boarders of the bondo. I've tried vinegar and evaporust, but neither one got into the scratches from the 80 grit paper well enough. Photo attached, if that helps at all.

 

Any suggestions on how to clean it up? I'm ready to get it painted and go cruising!

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I am using acid, it sucks but it has allowed me to move forward with my project.

I have found murriatic acid is boss, but it is tough. I use it only on items outside the garage in the back yard away from tools and trucks.

Just the fumes 10' away will cause flash rust on tools or trucks.

 

Ospho is good, I think in your case, it may be a wipe on wipe off issue. It will remove the new fresh surface rust, same time it turns old rust into a paintable primer.

So it is easy to paint over.

 

Also phosphoric acid is a good choice. I think this is my favorite. It will clean the rust & leave bare metal easier to dilute against flash rusting.

It is Food grade and used to remove rust on restaurant equipment. It does a excellent job removing hard water stains in a toilet bowl.

 

There are 3 different acids to use. My first choice would be ospho, then I would try phosphoric, murriatic is a tool for the metal in the sun for 20 years.

 

I am showing 2 photos, first it was previously cleaned then stored for a year. 2nd is after wiping it with murriatiac 

 

 

 

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Citric acid is awesome. You can buy this at Ace hardware and I guess a grocery store as I have read in forums.  I used citric acid to remove safely rust from my dodge truck body panels. It did not harm the paint. I use 2 cups of hot water to 2 heaping tablespoons of the citric acid powder. It dissolves better in hot water. I wear gloves and apply to the area needed sponging it on with a kitchen scrubby sponge. The fumes are negligible.  Do it several times and then use a 320 wet dry sandpaper to lightly lift it off. I used citric acid for decades in the printmaking arena: professional printing and teaching. 

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There is (was?) a specific metal prep made to deal with this.  It was phosporic acid based and left a phosphate coat on to prevent future rusting, for a limited time.  It also etches the metal to provide for a better bite. 

 

https://www.homedepot.com/p/Klean-Strip-1-Gal-Concrete-Etch-Metal-Prep-Rust-Inhibitor-GKPA30220/100406369#product-overview

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I paint professionally and my advice is to strip it with 80 DA and start over. Also, bondo is a 4 letter word, we prefer filler, haha. Lots of talc in it, sucks water like a sponge. Almost guaranteed to have rust under it. There is never a good time to rush when building a car but body and paint will cost you the most if you do. Redo a panel at a time and when the bodywork is done on each part, prime it and move onto the next. New hybrid epoxies are great and pretty inexpensive. 

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KBS Blast for rust, old bondo in appropriate bin. New polyester based filler over top of neutralized and primed metal surface. You NEVER apply filler over un primed metal. Use a epoxy primer since it will not shrink. Anything else is very marginal way to proceed and you will just be stripping off that newly applied paint like soon, as well as that bondo which was left there to economize. Word on that! M

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There are lots of schools of thought on primer and filler.    IMO and IME quality filler over bare metal is fine.  Was done that way for years.  But, if you prime first, use only epoxy as I know of no manufacturer that recommends any other.  There have been several tests done that show filler bonds best to metal, but epoxy works if done correctly.

 

Edit to add:  If one is applying to bare metal, it should be sealed with primer (preferably epoxy) as soon as shaping is finished.  That's because filler does absorb water and if allowed to do so before covering the metal underneath will rust.

 

As far as surface rust/metal prep I really like PickleX 20.  Darned stuff is expensive, but goes a long way and just works. 

 

And be sure to read the paint maker's tech sheets.  Some epoxies should not be applied over any acid based product, some are ok.  Some epoxies recommend scuffing before filler iif not covered after x hours.   x varies by brand and is important.

Edited by kencombs
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How do these methods recommended compare to something like Rustoleaom Rust Reformer Spray Paint or Rusty Metal Primer (not sure exact difference). 

 

I have used those recently for spray painting a metal wheel barrow with very good success, but if I were to use it on the frame or out of the way surface, or even on a panel and then prepped it with any kind of surface smoother.

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Just now, wagoneer said:

How do these methods recommended compare to something like Rustoleaom Rust Reformer Spray Paint or Rusty Metal Primer (not sure exact difference). 

You have a honest good question. The answer is not clear.

Typically people are using high dollar paint to restore these vehicles ... I am fine with that. There will be no talk about Rustoleum paint.

 

I am personally in your corner, I am not going high dollar on paint. I am using Rustoleum paint from tractor supply. I am fine with it.

I honestly feel the paint is as good or better when the cars were produced. ... Yes I know we have better paints today.

But the original paint lasted a satisfactory time period for me ... yes the newer paint will last longer .... sorry to say this, thats the next owners job & not mine. My job is to drive it.

 

So does the rusty primer work?  ... No clue, but by the time it fails I probably  wont care. If that makes any sense.

You will not get a honest answer here about Rustoleum primer because it will all be use epoxy primer. use this or that paint.

I am using Rustoleum  primer and also the paint. If I need to sand something off and repair, just not a big deal.

 

Just use what you want ... I have a strong opinion and you should do what works for you.

Mine is a driver quality truck ... you care about shows, you may not want to go Rustoleum.

 

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(This is a pretty long post, so feel free to skip down to the three points at the bottom)

 

I want to give a little more of the back story so you have a better idea of my expectations.

 

I got the car three years ago on a whim. I wasn't in the market for a classic car, but I saw it for sale and fell in love with it. It was a 10 footer at best, but the interior had been redone and the engine ran strong. I had a lot of fun that year running around in it. I put it in storage for the winter since I live in Indiana. 

 

Next spring, on the day I got it out of storage, a teenager side swiped it while it was parked in front of my house. To the kids credit, they did come back to tell me about it, but that was little solace since they didn't have insurance. 

 

The damage was more than I felt like I could repair, so I took it a local classic restoration shop. They told me that there would be a noticeable difference between the new paint and the old, so they recommend I paint the entire car. As you might imagine, between the repair and the paint it would cost more than I paid for the car. I decided to have them repair the damage since I wanted it done right, and have maaco paint it to save money, as I'm not wanting a show car. 

 

Well, $1000 and several months later, I got the car back. This post is already pretty long, so I won't go into details, but I could have fixed it better myself. So, perhaps ignorantly, that's what I decided to do. I stripped off all of their high fill primer and body filler with a sanding block so I could make it good enough that I could live with it. Like I said, I'm not wanting a show car, but I at least wanted the panels flat and lined up.

 

So, what I'm trying to say is:

 

1) I can't afford to put much into the car. I just bought it for a fun weekend driver and I didn't plan to invest in a paint job.

 

2) I don't need a show quality paint job, but I want it to look decent and protect the metal in case someone does want to put that much work into it in the future.

 

3) I don't have easy access to a da sander and I really, really don't want to have to strip the filler off if there is any other option.

 

I already have waaayyy more hours into it than I would like to admit, and the thought of starting over hurts my soul a little bit.

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I've said this before, so I'll be brief.  I used to work in a plating shop.  We used Muriatic acid in the process - Phosphoric acid is too slow.  But when you take something out of Muriatic acid, you can stand there and watch it rust, and it doesn't take long at all - like it'll be brown in 3 minutes or so.  (Different types of steel may react differently, that I don't know.) 

Phosphoric acid is totally different.  As Sniper already said, that's what metal-prep is made of.  I have an extra part that I kept from a blown engine I stripped of everything still useful, and after I took it out of the acid tank now 40 years ago, I never painted it.  It is still not rusted.  (As said, Phosphoric acid leaves a coating on it that blocks rust.)

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I just received an e-mail ad for this from POR15.  No idea how it would work but I can say everything else of theirs I used has done a good job

 

https://por15.com/products/rust-remover?_ke=eyJrbF9jb21wYW55X2lkIjogIlJQaEhTNyIsICJrbF9lbWFpbCI6ICJqdGFyd29vZEBhbWVyaXRlY2gubmV0In0%3D

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Sometimes I speak out of turn with little knowledge.  I did suggest acid. And it will work to remove the surface rust in Minutes.

Here is a photo of a experiment, a future project &  the paint was solid brown surface rust just on the hood in this area. I had a squirt bottle with ospho in it, wetted the area walked to the shop and grabbed a clean rag and walked back & wiped it off. Took about 1 minute total time.

 

You can see the film left on it. If this was bare metal would protect it from rust til washed off. When washed off you need to seal it with primer right away.

So this will remove your rust easily .... But will not fix your problem.

 

As suggested above, the bondo acts like a sponge and collects moisture. I would say digging out the bondo and start fresh is best answer. Panel is already rusting under the bondo & spreading out to where you can see it.

I was thinking this morning, maybe a guy could use a heat gun on the back of the panel and dry all the moisture out before you prime it.

The damage is probably already started, meaning the panel is rusting under the bondo. If you remove rust you can see, it will still show up later 6 months down the road.

3 hours ago, Wood and Steel said:

They told me that there would be a noticeable difference between the new paint and the old, so they recommend I paint the entire car.

Of course they said that, is how they put food on their table ... selling work.

A good painter can match paint .... the rest depend on Napa auto parts. If you can bring in a small painted part to napa, they can color match the paint for you and sell quart, gallon or even spray cans.

 

Knowing the situation, me being a thrifty guy (broke living on a fixed income :D ) Why not put it back together as is? I see a fender & wonder how much is disassembled?

I would remove the seen rust, use rattle can of rusty metal red oxide primer & paint all of the bare metal. And drive it.

You will know soon if the rust is going to come back. & will only be in the bondo area.  A future weekend project you can remove the bondo, seal the metal, fix the dent & color match the paint yourself. & still enjoy the car?

 

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Edited by Los_Control
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Although I expect primers(epoxy?) are better than years ago I remember being told that fixing rust and priming without painting was a short term fix as primer paints attracted moisture as they did overcoats. I do remember seeing cars in the past that had been fixed and primed that then were driven around for a while having rust visible through the primer.

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22 minutes ago, plymouthcranbrook said:

Although I expect primers(epoxy?) are better than years ago I remember being told that fixing rust and priming without painting was a short term fix as primer paints attracted moisture as they did overcoats. I do remember seeing cars in the past that had been fixed and primed that then were driven around for a while having rust visible through the primer.

 

I'm running into this as well with my first painting project. I want to prime some parts to get ready for paint so they don't rust, but It's unlikely I'll get to painting them soon. Is there a recommended procedure for preserving? I'm in a really humid area and coating it with an oil isn't particularly effective.

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Epoxies are best if you are planning on letting it sit. Depending on where you live, you can get good epoxy like ppg dp series. We can get it in California but it is reformulated. Primer isn't meant to be in the elements, it will absorb moisture. 

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One of my duty stations in the Navy was an antenna overhaul shot and being the junior man I got all the unpleasant job, painting antennas was one of them.  We used a two part epoxy primer and top coat on them.  They worked just fine even in salt water environments.  That was bad in 85-86.  Not sure how just the primer coat only would hold up though.  What you want is a sealer, not a primer, to prevent moisture issues.

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Sealers are meant to be topcoated within a time window. It's fine to let them sit over a period of time but like anything that sits, you will have to sand it and recoat. I've switched solely to kouse of kolor kd series of hybrid epoxy primers. It can be mixed as a regular build or high build primer and as a sealer to be topcoated. Having one product for everything is helpful. It is great over bare metal and filler.  I have even  used it on plastic and it bites like crazy. Also, it blocks like butter and is fairly inexpensive. It comes in a multitude of colors and they can be mixed together. 

Edited by allbizz49
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