Rust removal chemicals

[Seppi72]

I've been doing a lot of background research recently regarding how to (1) neutralize rust and (2) prepare bare metal surfaces for later painting. Item 2 leans towards keeping freshly-created bare metal (from sandblasting) from developing "flash rust" and then having a ready acceptance of a primer coat.

Anyway, I've identified three ways to get my metal to where I want it to be. All three are based upon the reaction of phosphoric acid with iron oxide (rust) to form iron phosphate. The first way is to use a product called Ospho (www.ospho.com). The second way is to use the PPG product tandem of DX579 Metal Cleaner followed by DX520 Metal Conditioner. The third way is to use the similar DuPont products 5717S Metal Conditioner followed by 5718S Conversion Coating.

From what I can tell, the primary difference between Ospho and either the PPG or DuPont systems is that the latter two also create zinc phosphate regions - particularly so on galvanized metal but they also contain a source of zinc - which is, DuPont says, supposed to be the best substrate for later paint adherence and corrosion resistance.

I have the MSDSs for the Ospho and PPG products so I can interpret them to gauge the concentrations of various active ingredients. Unfortunately, the MSDSs for the DuPont products aren't as detailed as I'd like for a good comparison:stupid:.

Curiously, the PPG literature says that "Metal treatment is not recommended or advisable on sandblasted metal" :eek: whereas DuPont has no mention of sandblasting, one way or the other. I've asked PPG for an explanation because it appears that everyone around this Web site swears by one of these post-blasting methods:cross-eye. I've also asked DuPont for its position on this matter.

Regardless of that technical issue, what is bugging me is the tremendous difference in retail prices that I have received from the various local suppliers here around Columbus, Ohio. This is what I've been quoted:

Ospho $8.49 per quart (local hardware store)

DX579 $28.99 per gallon (local NAPA store)

DX520 $26.99 per gallon

5717S $23.50 per quart (local auto body supply store)

5718S $23.40 per quart

So, after all this exposition, my question is whether anyone else out there has recently purchased any of these materials and whether the prices I've gotten seem reasonable. Frankly, it's only the DuPont pricing that has me wondering. Is it just this store padding its margins, or are all DuPont products similarly out-of-line price-wise?

[MEZZZ]

METALPREP ~ Item Number: PPG DX579-QT

List Price: 14.61

Your Price: 12.70 (QT)

Total On Hand: 6 (QT)

Here is a price from a randon website I pulled , they seem to be gouging alot more than your local NAPA store on the DX579.

[JimmyZ]

Ospho $8.49 per quart (local hardware store)

DX579 $28.99 per gallon (local NAPA store)

DX520 $26.99 per gallon

5717S $23.50 per quart (local auto body supply store)

5718S $23.40 per quart

Is it just this store padding its margins, or are all DuPont products similarly out-of-line price-wise?

The prices seem pretty close to what my PPG jobber charges for the DX and the Ospho. (gallon size) Remember that the DX gets diluted with water too. You get more than a gallon. It does eat up spray bottle mechanisms though.

Jim

[Bruce Palmer]

Jim,

Are you working with white metal or rusty steel? OSPHO being a convertor, I believe will need a rusty surface to convert. Sounds like the others may as well.

[trykflyr]

I'm using a product called Rust-Prep by Autotech. Comes in 16 oz spray bottles from the local auto/aircraft/marine paint supply shop. I have to remove the loose stuff before using it and then just spray or brush it onto the surface. It creates a zinc phosphate surface ready for priming. I've used similar stuff on aluminum, but it was a 4 step acid etch-rinse-conversion coat- rinse process. This appears to be working really well and ran me about 10 bucks. I don't know what Lower 48 pricing would be, but we're usually quite a bit higher.

[Seppi72]

I spoke with a PPG Refinish tech help line rep (1-800-647-6050 options 1,1,3) this morning and asked her two questions about the statement "Metal treatment is not recommended or advisable on sandblasted metal."

1. Why is treatment not recommended?

2. What does PPG recommend to prevent freshly-sandblasted metal from flash rusting?

Her answers were:

1. Sandblasting leaves many microscopic pits where the acid can get trapped and cause paint adhesion problems later on.

2. Prime freshly sandblasted surfaces with epoxy primer.

Regarding Answer 1, I would have thought that adequate rinsing would remove any residual acid. However, it may be PPG's experience that this is precisely what many people do NOT do. Enough complaint settlements and I can see this caveat getting put on a datasheet.:laugh:

But doesn't sanding leave microscopic, and somewhat irregular, grooves in the metal? Couldn't metal treatment chemicals become trapped there too if the parts aren't adequately rinsed? Someone who knows about metals, let me know the answer(s). I'm curious.

I've asked Ospho's Technical Director (as well as DuPont) about any concerns they have regarding treating sandblasted metal and will post their replies when they come in.

[five&dime]

Hmmmm. I have always been told to use PPG acid etching wash primer on bare metal. And then epoxy primer on that. That's how I did my 510 hood. I was told that it's not best practice to shoot epoxy primer on bare metal.

[trykflyr]

You want to shoot an etching primer onto new or bare metal. The etch basically creates a foothold for the primer to attach itself to the metal. If you don't have a somewhat rough surface (we're talking really small irregularities here) the primer will detach and come off in sheets. Think trying to paint a highly polished supersized ball bearing. The paint wouldn't stick very long.

[JimmyZ]

This is an excellent thread/topic so here's another bump.

People get away with painting over nontreated metal all the time. The question is how long does it take for rust to develop under the paint. My wife's volvo had some repainting done a few years ago with no treatment. They simply sprayed high build primer on some bare areas and sanded it. Now we have sheet rust in those areas. The paint has a raised and uneven surface from where rust is festering underneath. For production style bodyshops such concerns about longevity are thrown to the wayside. Turnover is all important and in time they forget about how to do things right. It's more about what they can get away with.

Looking at the attached photo you'll see a sandblasted windshield channel. Look closely and you'll see tiny pockets of leftover rust. You could paint over them but what would happen in a few months would be predictable.

Old metal which has rusted this thoroughly needs to be chemically treated. This eliminates or at least slows the spread of rust. Newer cleaner metal requires less severe chemical treatments or just ZC primer.

RE: Drying and removal of chemicals...

Most people (Hobbyists/noobs) don't dry their rinse water off as quickly or thoroghly as they should. This will cause sheet rust later. You've got to use clean dry air and a towel/clean wipe followed by a trip out in the sun to bake. This is the best insurance.

2c

Jim

[Seppi72]

After getting the info above from PPG, I've decided that we will take a hybrid approach. After sandblasting, I'll take a magnifying glass to the metal and look for any residual rust pockets. If there are any, they will get treated. Otherwise, we'll just spray epoxy primer on the fresh sandblasted surfaces and go from there.

However, I'll keep adding to this thread as I hear back from the two remaining suppliers; DuPont and Ospho.

[Seppi72]

I had a couple of e-mail exchanges with Ospho's technical director yesterday and told him of PPG's recommendation against using phosphoric acid-based treatnments on sandblasted metal. Here is the set up and his reply.

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Set Up

...when I was reading the PPG literature (Document P-226) on its metal treatment products, I saw that it has the statement "Metal treatment is not recommended or advisable for sandblasted metal." I called the PPG help line and was told that the presence of small pits in sandblasted metal could "trap" the acid and lead to paint adhesion problems down the road.

Does Skyco (N.B. the company that makes Ospho) have any experience with or similar reservations regarding the use of Ospho on sandblasted metal? I would have thought that adequate rinsing should remove any residual acid - but perhaps it's just PPG's observation that this is the one thing that people do NOT do. Doesn't everyone read and faithfully follow label instructions?

Reply

And yes, rust pits and sand blasting pits will trap acid/water requiring significantly longer drying times before overcoating. This would seem to be obvious, but . . . . . :stupid:

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It doesn't sound to me that he is rejecting the use of Ospho on sandblasted metal. Rather, I hear him saying that you have to do an adequate rinse (or maybe a couple of rinses) and allow the surface to fully dry.

I might just follow up with him a bit more next week. I've gotten really obsessive about wanting to KILL any rust that might exist on my car's body.

[geezer]

Bob, I learned a long time ago that white sandblasted sheet metal doesn't need any further chemical etching to promote adhesion. I do agree on the need for a clean surface before coating. PPG has never steered me wrong yet.