rust pitting clean up
 

hi i have a 56 hood that is perfect with no dents but has some rust on the top that has some pitting . to deep to sand out was thinking of sand blasting but scared of warpage. I was gooing to use verry fine sand low pressure at an angel and make sure i keep moving around. What do you all think???? or is there a better way??? Thanks Denis

Re: rust pitting clean up
 

No need to worry about it. Epoxy primer will stop it from spreading and ruining your paint job.

Re: rust pitting clean up
 

When you say "sand", I wouldn't recommend using sand as most of it also contains caustic salt particles. Not something you want in your sheet metal. We use the Barton 80HPA (garnet) for our media blasting.. As you said, light pressure and angled approach should keep things damage free. If you do blast the inner structure, block off any adjacent areas of the hood skin or open holes, and sand these areas by hand or DA. If you read the sticky thread "Repairing Sandblast Damage", most damage to hoods and trunk lids comes from someone attempting to clean off the inner structure and inadvertently hitting the adjacent flat sheet metal, which is more prone to damage than the multi-folds of the inner structure.

Re: rust pitting clean up
 

MP&C what i ment with the sand is sand blasting sand 50/100 bought in bags and yes did see the post on sand blasting . Sand is very fine what air pressure would you recomend i was thinking about 80 psi. Thanks Denis

Re: rust pitting clean up
 

Duramax, please research epoxy primer more before you do anything else.

Here's a random google search result about epoxy primer prep "example" of a TDS...https://www.paintdocs.com/docs/webPD...E&prodno=B58R8

Where in the attached does it say anything about prep for rust pits?

Specifically it says "Surface must be clean, dry, and in sound condition. Remove all oil,
dust, grease, dirt, loose rust, and other foreign material to ensure
adequate adhesion."

This is a standard SSPC coating application specification used in the industry.

SSPC standards are:

http://www.blastal.com/images/SSPC_Chart.pdf

You are not going to find a SSPC-SP5 as a prep for epoxy primer.

Ask anyone NACE certified if you should be blasting, and they will tell you "no".

Sand blast if you don't believe me.

Re: rust pitting clean up
 

Theres lots of different medias to blast with...on my truck they used coal slag and low pressure...it was all flawless until they did my doors...even with me warning them to be cautious, they made a mess out of them...
it was just as Robert(MP&C) said..it happened when they blasted the inside of my doors around the inner brace....
everything else they did turned out great..it was much cheaper for me to have it done than do it with my blaster..

Re: rust pitting clean up
 

No they didnt...they tried to tell me the doors were that way before...I even showed them pics of the doors before and after...didnt seem to matter...
So with alot of advice from MP&C and others ,and alot of hrs of work ,i finally got them good enough that a skim coat fixed it

Re: rust pitting clean up
 

Foot stomper thanks for the info looked at both and on the second search where it says blastal about midel of page they talk about removing as much or all of the scale rust before priming. Then i looked at your build nice job. Looks good in that colour

Re: rust pitting clean up
 

Thanks Duramax. Scale rust flakes off easily. Wire brush is adequate for prepping steel for epoxy. The key is to remove any debris, rust or dirt that can be removed without blasting.

Re: rust pitting clean up
 

Sorry, but I disagree.

NACE certification is not something I have, but am very familiar with the certification nonetheless. In the attached, SSPC.SP2 and SSPC.SP3 are the standard for metal prep before epoxy primer. Nowhere have I ever seen a Technical Data Sheet (TDS) where it calls for SSPC.SP5 ("white metal blast"). If anyone has one that calls for SSPC.SP5, I'd like to see it.

For more information on what NACE is, click here https://naceinstitute.org/Certificat...QaAiVTEALw_wcB

Cheers

Re: rust pitting clean up
 

thanks for all the replies and info

Re: rust pitting clean up
 

I looked at both House of Kolor and SPI, although they don't reference an SSPC standard, they both require removal of rust..


Attachment 1907373


Attachment 1907374


In looking at the NACE certification, as well as the Sherwin Williams Epoxy tech sheet, they both seem to be geared more toward an industrial application, where perhaps pitting in sheet metal is not an everyday concern.

Personal experience with severe pitting has shown a hard rust scale inside the deep pits, and although I did not use this tailgate skin, I did test some of the pits for removal methods of the scale. I could not remove the scale completely with either a wire brush or a crud thug. Only when using media blasting was I able to completely clean out the pits. Why is this important? The scale left inside the pits tends to re-activate in the presence of welding, such as someone fixing a couple holes from the outside, not knowing what lies in wait nearby. So although the holes showing from the outside appear to be manageable with a quick zap of the MIG, the inside view shows a completely different story, and demonstrates that this needs to be fixed properly BEFORE the paint goes on, lest you see more holes in a year or two.


Attachment 1907375

Attachment 1907376



My preference is to clean any pits to clean metal, then make any repairs needed, up to and including replacement sheet metal. My experience has shown media blasting the best method to insure the pits are clean, as well as the best abrading method for either epoxy or powder coat adhesion. Your vehicle, your choice in the repair methods and the extent of the repair.

Re: rust pitting clean up
 

thanks MP&C i agree that i want all scale out and will be blasting with low presure and the finest sand blasting sand i can find have spent to much time on this build to have rust come back in a few years. i have a blasting tank and can do it my self just hope i dont warp it.

Re: rust pitting clean up
 

SO how about wire brushing then an acid dip, either oxalic (weak) or phosphoric (leaves phosphate coating), before epoxy?? I've got some parts that are lightly pitted in areas I don't want to sand heavy (think center of roof!!) but don't want to ever see rust there again.

Re: rust pitting clean up
 

I have heard some epoxys don't play well with phosphoric acid, read the data sheets before you try it.

Re: rust pitting clean up
 

In the grand scheme of things, the primer needs to be SLIGHTLY acidic to get good adhesion. Too much acid, like a coating of your phosphoric acid residue under the epoxy, and the acid starts to do what acids do. Typically this would be the deposits left deep in pits (see my post above) since they are difficult at best to remove. This normally results in acid activating after a few months in sunlight and you'll start to see small circular raised areas (about 1/8 diameter and less) in the paint finish as the paint delaminates above this residue from the gases given off by the chemical process occurring..


Too much base, as in you used soda blasting without proper neutralizing, and any SLIGHTLY acidic properties the epoxy USED TO HAVE is neutralized by this presence of a base on the metal surface, where it no longer has adhesion. Hence, your paint will pull off in sheets.


So when you hear me preach media blasting (by a qualified person) over any quick fix rust encapsulator/converter/snake oil to address pits, this is the reason why. Media blasting using garnet or coal slag types (Black Beauty) does not cause a detriment to ADHESION like some of these other processes do. When you have to repaint a car, and all the labor and materials that go with that, you'll get it. Let's just say I get it, and it was a lesson based on the owner's generous application of Ospho that was deposited in pits. I'd say take the learning curve while it's cheap.


Disclaimer: Yes, media blasting will cause stretch damage. If you don't know what you're doing, research, research, research. That applies to whether you are doing it or you're finding someone else to do so. If a DA and 80 grit will remove the surface rust, so be it. If it is pitted, the DA won't address all the damage and you're now onto the next option.

Re: rust pitting clean up
 

OP, take a wire wheel and remove all the rust down in the pitting. Yes it takes time but try to get all of it out. You cannot put epoxy over rust. the epoxy may slow it down but any rust that is left under it will eventually spread. after removing just put the epoxy on then bodywork on top of that.

Re: rust pitting clean up
 

We were in the same situation with an F100 hood a few years ago. The battery had exploded and the inside of the hood had deep rust pits that sanding alone wouldn't remove. We used repeated soaking with naval jelly and scrubbing with wire brushing to remove all the rust without resorting to blasting. It took a couple days of soaking and scrubbing to get all the rust out. Once the rust was all out we used scuff pads and PPG DX579 and DX520 to neutralize the naval jelly and prep for epoxy.

http://i1315.photobucket.com/albums/...48709476_n.jpg

http://i1315.photobucket.com/albums/...79185913_n.jpg

http://i1315.photobucket.com/albums/...58285316_n.jpg

http://i1315.photobucket.com/albums/...09992432_n.jpg

Re: rust pitting clean up
 

theastronaut yhanks for the info seems to have worked well. Where can one get that navel jelly and what is it Thanks Denis

Re: rust pitting clean up
 

Max55..its a rust dissolver...you can get naval jelly just about anywhere that has paint supplies..summit, and Eastwood's has it I know