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Acid Dip or Media Blast?


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What is the preferred method to do a car "right" and perform a concourse restoration these days on a 71-73 Mach 1/Boss?  I am interviewing two shops, one is suggesting the full acid dip and the other is saying they prefer media blast.  The car does have quite a bit of rust and has been a midwest/northern car most of its life.  The car has sentimental value so I am wanting a "no expenses spared" restoration and it will remain in our family forever--I want the restoration to last.  The car was undercoated when new, but we are looking to go back to red oxide floors, etc     

 

 

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Edited by CLASSIC MUSCLE
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I'd go for dip vs blasting without hesitation.

The phosphoric acid is not just removing rust, it leaves a protective layer and it will go where blasting can't.
I would also inform about their pre acid methods (how they remove grease, paint, glue...)  and post acid methods. Some spray temporary primers, some use KTL ( http://www.elameta.lt/e-coat-ktl.html ) and some do nothing aside hot dry after rinse. 

Sand blasting is very destructive despite what many say. The only blasting media that isn't creating damage on thin metal is soda (or some soft nuts shells), but this is only for surfaces that are not rusted and it's used to remove the paint. Soda will not even remove "deep" rust. Sand blasting is fine for thick metal parts.

if I look at your pictures, I would consider look at what needs to be changed first. Because if you need to replace a lot, which you will have to replace anyway after a dip or blast.
The question would be is it worth it. I mean by that, that if you end up with lots of metal changes ( your picts kinda say lots will need attention if you go for concourse), you can also use the good old elbow oil with paint remover for the parts that are just in need of a new paint. 

 

Edited by Fabrice

73 modified Grande 351C. (Finally back on the road woohoo!) 

71 429CJ. ( In progress )

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There is a lot of metal there that will have to be replaced. You will have that car disassembled so far that you will be able to sand/ wire wheel inside frame rails, probably looking at full floor, cowl, maybe even some rocker panel repair. At that point you will be accessing most of the cars hidden places, so I wouldn't pay to have everything stripped that you are going to replace. Also for a project that extensive, you will want to make sure you brace everything or Jig the car. I live in Minnesota so I see this kind of rust all the time, I also had a 1973 that looked really clean until I dug into it. The front frame rails above the upper control arms were rotted out where that little shelf in there is, the tail light panel and trunk were toast, and every engine compartment apron had rust where yours does. Also my cowl extensions and cowl hat area was rusted out too. I'm not trying to scare you, just trying to let you know there is always more rust than you see initially. Good Luck!! These cars are worth saving!!

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Currently I am in the process of preparing my car to be dipped. Preparing really means stripping and welding in patches where necessary. You may end up reaching most hidden spots but I doubt all of them. To reach that 100% score I decided to aim for dipping it 3 times:

1 - Strip bath

2 - Rust removal bath (where it gets a protective layer)

3 - Base coating bath using Electrophoretic deposition (EPD)

I had a standard hood dipped that way and I was very pleased with how it came back. It now sits in storage, totally rust free wearing a base coat waiting until the rest of my car is ready for it :-)

Good luck with your project!

Vincent.

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20 minutes ago, Vinnie said:

Currently I am in the process of preparing my car to be dipped. Preparing really means stripping and welding in patches where necessary. You may end up reaching most hidden spots but I doubt all of them. To reach that 100% score I decided to aim for dipping it 3 times:

1 - Strip bath

2 - Rust removal bath (where it gets a protective layer)

3 - Base coating bath using Electrophoretic deposition (EPD)

I had a standard hood dipped that way and I was very pleased with how it came back. It now sits in storage, totally rust free wearing a base coat waiting until the rest of my car is ready for it :-)

Good luck with your project!

Vincent.

I’m curious, did the insulation material the factory installed between the upper and lower panels when fabricating the hood, stay in place during the dipping process? I chose not to have my ram air hood and trunk lid dipped when I did my car for fear that this material might be compromised with no way to reinsert an insulating material after the fact.

"Yes dear", has kept me in the hobby a long time...

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I chemically stripped my car (back when you could get good stripper) and then media blasted it with a fine glass bead.  I am convinced that my car will trickle out tiny bits of glass bead forever- even though I did everything I could to blow it out of every possible place.

If I could do it over again I would have put it on a trailer and driven it 5 hours to the dipping place.  Having the car shell itself (and maybe your doors if you choose to use them) is a massive labor saver.  The fact that everything will be clean bright metal will reduce repair time and make it a whole lot cleaner for the shop doing the work.  It will also show every flaw, which will allow you to take all the damage in at once and do a final reality check on what it will take to make your car a car again.

As for the Hood and trunk lid, I would not have them dipped because it is probably easier and cheaper to replace than repair.  The trunk lid shows rust on the outside, and I cant imagine your hood is much better.  Both of those can be found in much better shape used, or repop new.  I don't think the dip would remove the putty / goo that is used to connect the inner and outer stampings but that is a good question for the dipping place.  The videos the dipping place in Oregon has produced show that much of the putty / filler remover is done mid dip, where they pull the shell out and use a high power pressure washer to blow all that stuff off once loosened.  My impression from what I saw is that the material inside the hood and trunk would remain as they can't really get to it with the pressure washer / scrapers.

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Dip it for sure. Much more work. You won't believe what will be reviled.

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I guess I am in the minority here, but I am a fan of media blasting. Not sand, but plastic media. It in no way heats up the panels and when my 67 Camaro got finished there were still pencil marks left over from the factory on the body panels. It literally just took the paint. It was pretty cheap where I had mine done, but that was some time ago. 
 

Obviously if you are going to go the full way with dipping, that’s very cool too; I am not badmouthing it in any way. But I do think it’s more expensive than media blasting to do it right. I have seen improperly neutralized cars have acid leak from seams years later and destroy great paint jobs, so be sure to verify they know their stuff and have adequate steps to eliminate the acid. If everything is done correctly though, and the car is dipped in an epoxy primer at the end, it is very cool to know that all your panels are covered every which way for rust protection - inside and out. I am thinking of the cowl and rockers specifically.  
 

If you are replacing a bunch of stuff anyway though, I’d be strongly tempted to just media blast, and make sure insides of replacement panels are covered properly.  

 

Just my opinion. 

Lazarus

 

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23 hours ago, 7173Vert said:

I’m curious, did the insulation material the factory installed between the upper and lower panels when fabricating the hood, stay in place during the dipping process? I chose not to have my ram air hood and trunk lid dipped when I did my car for fear that this material might be compromised with no way to reinsert an insulating material after the fact.

There was none left in the hood I got before dipping. And when dipping, you should assume nothing else but metal will survive.

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1 hour ago, Vinnie said:

And when dipping, you should assume nothing else but metal will survive

Actually its not the acid that would alter/remove rubber, glue, grease... (I've actually used grease to mask some parts regions when I acid bathed them and grease remained)
The pre acid treatment is what will degrease, remove the paint, dissolve insulation etc..  The acid pass will only remove/convert the rust.

73 modified Grande 351C. (Finally back on the road woohoo!) 

71 429CJ. ( In progress )

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I'm sure that there's a right and a wrong way to do the acid bath...that said, I had a good friend that had his '56 Chevy frame ruined by an acid bath due to micro-fractures in the frame's metal being seeded/penetrated by the acid; Also, I've heard good things regarding using almond or walnut shells for the media if you want to preserve rubber etc. but still remove oxidation and paint

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6 hours ago, Bentworker said:

That's a great write up on the process; that said, given the parts were soaked in an acid and then pressure washed to remove the agents, I'd be leery of the pressure wash's efficacy of getting into the proverbial nooks and crannies. I'm sure that finding the correct shop would be key to ensuring that the last process completely removes the active chemical agents. 

 

Edited by autonomousbronco
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9 hours ago, Vinnie said:

There was none left in the hood I got before dipping. And when dipping, you should assume nothing else but metal will survive.

Agreed, hence why I would not risk my hood or trunk lid. So what are you going to put between the metal pieces?

"Yes dear", has kept me in the hobby a long time...

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6 hours ago, 7173Vert said:

Agreed, hence why I would not risk my hood or trunk lid. So what are you going to put between the metal pieces?

Truth be told, at the time I didn't know there was some kind of insulation between the skins. I only saw the glue at places where the skins touch and figured that can be put back. Something I had not mentioned I believe is that my dipped hood is a standard hood, the kind that is not reproduced. This kind is more open than the ram hood and it may be easier to get insulation in it.

 

But while we're at it, what exactly is this insulation for if both skins are also held together with glue?

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14 hours ago, autonomousbronco said:

That's a great write up on the process; that said, given the parts were soaked in an acid and then pressure washed to remove the agents, I'd be leery of the pressure wash's efficacy of getting into the proverbial nooks and crannies. I'm sure that finding the correct shop would be key to ensuring that the last process completely removes the active chemical agents. 

 

When you use phosphoric acid that is not a problem as it only eats rust and not good metal. Please correct me if I'm wrong!

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8 hours ago, Vinnie said:

When you use phosphoric acid that is not a problem as it only eats rust and not good metal. Please correct me if I'm wrong!

Again, theoretically, just like buffing paint, if done properly and with the correct materials, it shouldn't be an issue and you'll have great results. That said, if done incorrectly, well...we all know the rest. I was just stressing the importance of finding a good shop; I like WOM (word of mouth) rather than online google reviews as those can be "optimized" i.e. manipulated for the right price. 

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9 minutes ago, autonomousbronco said:

I was just stressing the importance of finding a good shop;

Yes, tho, now days with the environment laws, recycling investments they must do, most these companies use more or less the same stuffs. Unlike a decade or more ago.
And if they'd ruin cars on regular basis, considering it's mainly done on cars worthy to be saved and often pricey, rare. I don't think they'd be long in business if they were damaging the structural integrity of these cars.

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73 modified Grande 351C. (Finally back on the road woohoo!) 

71 429CJ. ( In progress )

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8 minutes ago, Fabrice said:

 

Yes, tho, now days with the environment laws, recycling investments they must do, most these companies use more or less the same stuffs. Unlike a decade or more ago.
And if they'd ruin cars on regular basis, considering it's mainly done on cars worthy to be saved and often pricey, rare. I don't think they'd be long in business if they were damaging the structural integrity of these cars.

Just a consideration, regarding “ruining cars,” it might take a decade or so for the damage to become visible given the affected spots would be in locations that aren’t easily gotten to by a pressure washer.

 

Also, regarding phosphoric acid, no that wouldn’t be an issue but rather protective if it reaches the caustic agents to neutralize and then protect said metal. 
 

Again, theoretically the process should be sound so long as done properly. 

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As far as gluing the skin of the hood / trunk back on.  I played around with an old hood taking it apart to make a cowl hood out of it.  The factory adhesive was cream colored and the consistency of a racket ball.   It could be released with a heat gun.  Figured if I ever had to glue one back together I would drill small holes (using a drill with a stop collar to avoid damaging the skin) through the bracing.  Then get some sealer that was pretty thin and inject it through the holes.

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Just thought Id throw in my 2 cents... I worked at an auto plant for 20 years and the glue we used was butal rubber . and construction adhesive. also its been my experience with phospuric acid that it coverts iron oxide or rust to phospuric oxide but only whats penatrated, so you could actualy have red rust under the black oxide.If it were me, I would buy another shell that you could blast dip weld  prime and paint, then remove parts from your car to install on the restored shell. Also I think zinc primer is the way to go. Been on my truck for 20 years. Again just my 2 cents.

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  • 4 weeks later...

I am fortunate that I live pretty close to Carolina Chem Strip. They do cars all the time and they did one I was hoping to be finished with and crushed a disc. I also have a friend that has been restoring cars for 36 years now. He has never advertised and does not have a web site does not need one has a waiting list always. He also uses Carolina Chem Strip.

The first place you go with any ground up restore is a frame shop to have what is left of the chassis put back as close to zero as possible.
What ever shop you use has to have a chassis JIG or they do not know what they are doing.
For a car as rusty as that one there will be at least 2,000 hours of labor plus all the materials and parts.
There is a shop near Atlanta that does only panel replacement and no body work. One of our members, that I will not call his name, had them do the panel replacement on his car which was inner fenders, cowl, floors, some frame, trunk, quarters, wheel houses pretty much the whole chassis. The car then went to a body shop that worked the metal fit the gaps and painted it. This car won best of show with over 1,000 mustangs entered this year. So that speaks highly of their work and they are not expensive either. They are Grave Robbers and I will have to get a link to their site. https://www.graverobberssheetmetal.com/index.php/custom-frame-jigs
You take a bare dipped chassis to them to work from.
Now back to dipping,they use a combination of ovens and dipping to remove all paint, sealer and of course rust. After it is all clean they wash and then do phosphate coating that will prevent rust in a shop for months while panel work is done.
The car that I have has been sitting over 10 years now with just epoxy primer on if for now and no issues. You will not get bleeding from seams like some say the dipping does.
Your car has pop open gas but 73 side stripes. A 73 will not have red oxide primer but will be gray and not slop gray but gray epoxy primer. All 71 and some 72 will have red oxide you need to find original paint and primer to know for sure.
The cost to dip was around $2,100 but has probably gone up like everything else. What is left will be filled with pin holes but most of the car will require replacement for sure. Here is link to Carolina Chem Strip. https://chem-strip.com/portfolio/
Someone said something about insulation in the hood on these cars. There is no insulation inside the hood. There is dabs of seam sealer between the inner and outer hood to keep it from vibrating. E-coat was also mentioned but E-coat will not get between the inner and outer hood stampings. There is not enough flow of material to get a coating inside. The tank is not all paint but about 80% water with 20% paint in suspension and the electrical charge pulls the paint out of the water onto the metal.
I would expect the restoration to cost well over $100,000 probably $150,000 for a true Concourse Restoration. It will take a minimum of a year and the painter will need to let the primed and body worked car sit for couple months to allow the primer and bondo to shrink before final blocking. Now please remember that Grave Robbers is not a body shop. Any bare metal will get epoxy primer but no body work will be done.
I know you say the car is sentimental to your family but you are going to end up with a mustang made in Taiwan. You would be way farther ahead to find a rust free California or desert car and move the VIN# and drive train. You are legally not allowed to do that but some people do. Would be better than repo sheet metal. I was an automotive product, process and tooling engineer for over 25 years so I know metal. The repo metal is much softer to all it to form easier so if you lean on a quarter panel you will probably put a big dent in it.
I picked up a totally rust free 1973 Grande from Arizona that will go to dip strip and then make a track days car. It was only $1,000 and was loaded with great options. Not even the battery box is rusty.
My friend with the restoration shop had done a camaro that all that remained from original car was the windshield frame, A posts and the part of the cowl with the VIN#. Every other piece was changed out. AMD in Atlanta did panel replacement and he did body work, paint and assembly.
Like me he has bad back so is stepping away from builds like that and going to lighter easier work.
So it might cost you some shipping to get the body to Carolina Chem Strip and then to Grave Robbers but you will save tens of thousands of dollars. You can probably get a little saving on the dip if you do only pieces you will be using and not pieces that will be tossed.
If you find all the parts you will save a 15% mark up by the shop usually. Grave Robbers buys so many panels they get them cheaper also. Some of the parts are not made so will have to be rebuilt. Not for the faint of heart.

When a man is in the woods and talks and no women are there is he still wrong??:P

David

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  • 2 weeks later...

Thank you David. Enjoyable and informative read. What's your take on Dynacorn body's. I know it's not made yet for our cars but it's only a matter of time and might be worth the wait. I have  a 67 camero that I did up 30 years ago and needs it again. I was thinking Dynacorn. Part of the reason is the instant gratification of removing a part, restoring it,installing it. I tend to loose interest when overwhelmed with a project. Was thinking a dynacorn could be shipped directly to the paint shop and I could have a shinny red shell to start with. Again thanks for your input and opinion.

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