Acid Dip or Media Blast?

[CLASSIC MUSCLE]

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     

 

[Fabrice]

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. 

 

[Omie01]

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!!

 

[Vinnie]

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.

 

[7173Vert]

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.

 

[Bentworker]

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.

 

[Ryunker]

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

 

[Lazarus]

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. 

 

[Vinnie]

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.

 

[Fabrice]

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.

 

[autonomousbronco]

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

 

[Bentworker]

http://www.metaldipping.com/our-process.php

 

[autonomousbronco]

http://www.metaldipping.com/our-process.php

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. 

 

[7173Vert]

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?

 

[Vinnie]

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?

 

[Vinnie]

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!

 

[autonomousbronco]

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. 

 

[Fabrice]

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.

 

[autonomousbronco]

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.