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  #31 (permalink)  
Old 09-29-2004, 10:52 AM
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rust

of all the wonder products sold today i have yet to see a can full of insulators.. cut it out or cover it up but you cant stop it.. we just finished a 55 in the shop that was blasted at home. totally destroyed. without skimming the entire car with bondo there is no way to repair it. the owner just opted to paint it and live with it. looks like it sat thru many west texas hail storms from all angles.

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  #32 (permalink)  
Old 09-30-2004, 12:05 AM
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Quote:
Originally posted by TurboS10
I am curious about the statement about sandblasting increasing rust problems. I am not body expert, but I have to disagree. If all the rust is removed and the metal is sealed the rust should never come back. I blasted the body on my 57 about 12 years ago.....yes, I was only 15 yrs old.......and it has had no rust come back. I would suggest a defferent media than most of you have probably heard of. Blow sand from a local farmer works wonderfully. It has rounded edges so it is much like soda blasting and leaves a nice smooth surfage. Of course it depends on where you live whether or not you can get the sand, and you have to sift it before putting it in the tank.

Chris
Chris,
You said you were interested by my statement about blasting and rust coming back. These parts were blasted in a wheelabrator which uses steel shot (which are extremely small round steel balls) As far as something being round, the reason why something may appear to be smoother is that the round spheres actually create small dishes in the material WHICH reflects light easier and MAY APPEAR and FEEL to be smoother, but in reality can have a signifiganlty coarser micro-finish. The only true way to measure surface finish is with a device such as a profolimeter. You can take steel grit or chilled iron for example, and create a finer finish than say with spheres. The difference is the way they cut and the surface finish profile they leave, but not necessarily how well they remove material or how quickly they can cut. I do this kind of work for a living and have been doing so for the last 20 plus years. The reason the rust probabaly returned so quickly in these areas is that they were pitted to start with, and the media did not completely clean the area even though it appeared that way by eye. Then in turn by not being sealed, they started to rust prior to the other parts. One of the ways that many industrial rust inhibitors work is that they CLEAN the metal, not necessarily coat the surface. Most are very astringent cleaners. I pose this question to you. I just recently stripped my 49 Chevy. It had seven layers of paint with one of the top coatings being PPG DP90 Epoxy (the old good stuff). In many areas where the paint and sealer looked good, the underlying metal had surface rust, not the kind that is rough or pitted, but still visible. It probably was more from something prior to being painted, but could it be that all coatings absorb moisture to some extent. I know that the best epoxy marine coating tech sheets say that they absorb up to .02% in a 30 day period, not much, but permeable none the less. If this is the case, then I would suspect it to be true of most coatings to some extent. I am not sure if this is the cause for some rust, but I would not bet that your Chev does not have some rust under that paint. Maybe not visible, but still there I would bet.
Hey, I got an idea, how about you go strip your Chev down and prove me wrong.Send pics
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  #33 (permalink)  
Old 10-02-2004, 06:03 PM
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cut the old metal out put the new in


its not that hard!!

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  #34 (permalink)  
Old 10-02-2004, 10:27 PM
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Belaire,
I have been cutting, shaping, welding and finishing metal longer than you have been alive. Yes, sometimes it is that hard.
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Old 10-02-2004, 11:31 PM
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Well said Ron. I'm getting ready to do my first cut out and reweld job, and I can't be prepared enough. I'm a bit worried abouthow it will turn out but none the less confident.
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  #36 (permalink)  
Old 10-03-2004, 07:08 AM
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Like I say all the time, I am no expert.

If sand blasting and chemical coatings will not keep metal from rusting, I guess we are all just SOL. BarryK is a pro and seems to think that sandblasting causing rust is a myth as well. Perhaps I have missed the meat of this thread, but what would you suggest doing when an car body is completely covered in pitting surface rust? My 57 was about 50 % surface rust when I got it. It only had the original paint on the sides of the doors and fenders.....pretty typical and not a cut and replace situation.

There is obviously a need to cut and remove and material where holes are present, but you guys make it sound like you need to cut and remove any place where a rust spot appears. Someone who read this thread could get that impression and it is simply not the case.

Chris
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  #37 (permalink)  
Old 10-03-2004, 09:35 AM
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Chris,
I think the their talking about panels with holes rusted through.

This is no doubt the most informed post on here with Brian researching the "at sea coatings" and now Ron brings up 2%
saturation on good grade epoxies. Deep!

The 2% qualifies the product as a waterproof product such as used for bottom paint (underwater) To relate this to your paint on the new car in the driveway (not waterproof) if submerged in saltwater with no air time the paint would start bubbling in 3-9 months. 2% is not enough to cause rust in anyway.

Bottom line on rust, if the metal is CLEAN and sand basting is next best thing to dipping and a waterproof NON solvent holding material is applied, IE; epoxy or zinc as martin said it is impossible for the rust to start as it needs either -solvents, moisture and air.
That is why acids etch have a long term problem as the Vinyl acetate holds air and solvents like a lacquer.

RE: Martins zinc rich primers, the only real use of this in our side of the business is in "weld through primers" in these cans depending on company there may be 75-95% zinc and the rest nothing more than suspension solvents for spraying. So ask some one that uses a lot of this type product and you will finds the spray cans have a high failure rate as zinc settles real fast.
This is why you don't find heavy zinc enriched primers in this side of the business as the second time you went to use that 2K primer the settling would be about unusable. Zinc is also very soft and sands bad.
In automotive the next best thing is Zinc Phosphate and you will find this in some of the better epoxies as its more stable (less settling) and actually bites the metal better than just plain Zinc and will at least be sand-able if needed.

Last edited by BarryK; 10-03-2004 at 10:00 AM.
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  #38 (permalink)  
Old 10-03-2004, 10:45 AM
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Recently, we picked up a new front clip for my 69 camaro and it was rusted up pretty good. It had been sitting outside for quite awhile. We were going to sandblast it, but no one in town we knew had a sandblaster, or a place that was open the sunday we decided to work on it. we disassembled the front end, a-arms etc... and dipped them in a 5 gallon bucket of muratic acid and let the smaller parts sit for about 10 minutes. The larger part, the frame, we leaned up against the telephone poll outfront and sprayed it down with a pump up sprayer filled with acid. all of our parts looked damn good after that. Looked just like new! After each acid dip or spraydown we rinsed each part off with the hose and dried it with a rag & compressor. We put them in the garage and it had been awhile since the last time we worked on it and they were still rust free, without any coatings. you can use a paintbrush to apply the acid onto an area. Just make sure you wear gloves and if you use the pump up sprayer, get a full body chemical suit, as this stuff is very corrosive! A respirator and safety goggles are a good idea too! the fumes that are released (hydrogen gas) smell awful! and when doing this, no smoking please. Hydrogen gas is highly combustible.

This is off the subject, but i might add that a few weeks later we took the a-arms, springs, etc... and coated them with a rubber undercoater. This was to try and take the attention off some of the pitting by making the surface pretty much the same. a few days ago we put 3 coats of primer on everything, then 2 coats of black high gloss enamel. It still looks damn good! hehe, now we're just waiting for my polygraphite bushings front end kit from pst to come in so we can put everything back together!

Last edited by rockport_juggalo; 10-03-2004 at 10:52 AM.
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  #39 (permalink)  
Old 10-03-2004, 10:59 AM
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Barry, I know the links were not to imply we should use the same techniques on our cars. I was only making the point that POR is not what they make it out to be, If that was the case it would be used on those off shore oil derricks.

How much zinc does the "E" coat have from the factory?

How does the zinc phosphate epoxy hold up against the zinc rich E coat?

Barry, your point on the etch primer soaking up moisture has hit home. I learned from S-W that the etch was basically a lacquer. Your added information (conveniently left out by S-W) that it can retain moisture really hit home with me.

On the rattle cans settling, boy do I know that one. When I was a rep I had to return cases of the stuff with the pick up tubes plugged! Not only that, S-W even made the cans smaller because there was just too juch zinc in the can to be of any use before the darn thing failed.
Not only that, but as far as I can remember there are strict recommendations NOT to paint over the weld thru primer. It was to be used as protection BETWEEN the metal lap and that is it.
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  #40 (permalink)  
Old 10-03-2004, 11:40 AM
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[QUOTE]Originally posted by MARTINSR
[B]Barry, I know the links were not to imply we should use the same techniques on our cars. I was only making the point that POR is not what they make it out to be, If that was the case it would be used on those off shore oil derricks.
***********************************************

I knew that, but was shocked no one asked why not?
So thought would cover it anyway.
BWK
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How much zinc does the "E" coat have from the factory?
**********************************************
I don't know? I would guess if it does its a Phosphate. (just for ease of use with equipment) I will try and find out next week.
BWK

*********************************************
How does the zinc phosphate epoxy hold up against the zinc rich E coat?
*************************************************
Last cross hatch salt spray test I saw (on an e-coat) was about 8 years ago and don't remember the company name
and it was good for about 900 hours.
Things change so don't know if thats still the case or they improved- could be GMW would be up on this?
So that would rank with the top 1% of epoxies covering all markets. Around 120-125 companies that make epoxies.
BWK
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  #41 (permalink)  
Old 10-04-2004, 07:59 AM
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during my time in purgatory [ usn ] i was assigned to airframes for a while. had to go to school to learn how to take care of planes. here is how it was explained to me. the rust you see is the byproduct of corrosion. caused by water/oxygen/electrolysis . rust poop for lack of a better word. rust lives in the metal not on it. i'm not an expert on metallurgy but i've been fighting this stuff for 35 years. you can slow it down, hide it or cut it out but you will not stop it with any wonder product out of a magazine.
now to sandblasting. we had to glass-bead blast the aluminum but were not alloyed to sandblast anything. reason given was sand is coated with salt. compressed air contains moisture. so in the process of sandblasting you would be applying a coat of salt and driving the rust into virgin steel. if your going to sandblast you need to remove some metal afterword's by sanding . ever notice a blasted car will have a little rust come out of folded areas and cracks? as i said i'm no expert but your best bet is to remove it. surface rust will not eat thru your roof but it will always be there. thats the reason your painter wants to use quality products instead of acme paint. :)
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  #42 (permalink)  
Old 10-04-2004, 08:29 AM
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Phosphoric acid or the other name magnesium phosphate will flat out eat runs off metal. On surface rust in 10 minutes it will eat it to sliver metal. On thick rust it takes longer and might need more than one application but it will take it to good metal.
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  #43 (permalink)  
Old 10-04-2004, 04:28 PM
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***********************************************
How much zinc does the "E" coat have from the factory?
**********************************************
I don't know? I would guess if it does its a Phosphate. (just for ease of use with equipment) I will try and find out next week.
BWK
*********************************************
******************************************
We got edumacated today!
I talk to three different auto manufacturers
two American and one foreign. Here is what I learned (how things change) Because of the panels being galvicoated etc, etc.
The E-coat used by most manufacturers at this point is a
waterborne primer, with a few still using epoxy but no Zinc Phosphates or Zinc. (Cost measures)
Thats why I called three as I know these guys, but not well enough to say I getting a straight answer but the story was the same at each place. In short the black coating is not what it use to be. The world is going to h***!
This just ruined my day.

Last edited by BarryK; 10-04-2004 at 04:35 PM.
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  #44 (permalink)  
Old 10-04-2004, 09:38 PM
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I may be beating a dead horse but I'll ask anyway. I have read in this post a couple people saying that sandblasting can cause rust. However dont most people use aluminum oxide for stripiing instead of sand nowdays and perhaps "sand" blasting would cause that but "media" blasting should not be a problem should it? I am not an expert this is just a general observation of what i have read so far so if I am wrong please let me Know.
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Old 10-05-2004, 06:31 AM
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Sand blasting of media blasting will not cause rust, I think that most people get confused here. Clean metal rust right away and I mean within seconds in some areas depending on humidity. So if you sand blast or media blast and clean the metal it will start to form surface rust even before you finish the project. Remember when you buy sheet or bar stock it has a thin film of oil on it, so if you blast to bare metal it will start to rust. That is why body shops have metal prep around, it contains some Phosphoric acid and will eat the rust then you need to get protection on it fast.

Today to many people draw conclusions with no real basis. I had my car painted and the transmission went out so that means painting a car is bad!
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