protecting my bare shell
 

im about to get my 911 tub blasted but the body shop that its going to gets quite damp at night, even with a dehumidifier running all the time. whats the best type of primer to use as a good metal protector while the body is being played with? i was thinking perhaps a cheap chalky celulose primer?
also, any views on the best medium for blasting? its a completely stripped tub.

Andy UK

For blasting I'd suggest plastic bead. There are many variations of this media and it can be done without harm to your galv tub...if it's coated in the first place. Soda blasting has also been suggested on this board. I don't have any experience with it but if you can find a shop to use Soda you may want to compare.

Regarding primer, that's a tough one as primer is not designed to be a toap coat and in some instance will allow moisture to penetrate.

epoxy primer?
 

Excellence featured a 930 daily driver with PPG epoxy primer and unpainted, owned by the PCA turbo guru. I can get more details when I get home.

Andy, Is the primer being used as a temporary rust prevetative (to be removed later) or as a permanent base. If permanent I'd suggest looking into the etching and Zinc Chromate primers.

I might be wrong but primers will not protect the metal finish from rust for any extended period of time. From what I have read about primers it is suggested that paint be shot as soon as possible. primers are porus and must be sealed with paint to prevent moisture and contaminants from getting to the metal and causing rust and paint lift (pealing) over time. Etching the metal will only protect the metal for a short period of time also (several days) and requires primer and paint ASAP. Sealing the metal with a product like POR-15 or equivelant product will protect the metal for a very long time period from moisture and rust. It would be best to shoot a layer of primer while the POR-15 is still curing to create a bond between the two. Otherwise you would have to sand the por-15 before priming at a later date. The primer will also require light sanding before painting if you leave it unpainted for more than several days. Sanding the primer would be much easier than sanding the POR-15.

I sprayed my tub with POR-15 and coated it with primer 45 minutes after the second coat of Por-15. The next day I lightly sanded the primer to remove imperfections and then shot the base and clear coat. I feel very confident that my car will not rust in the future with the POR-15 coating. Like anything else only time will tell.

Be careful with your primer choice...as in *do not mix paint systems*...
(meaning don't prime with a DuPont and top coat later with PPG, etc.)

Media blasting is great, however it will NOT remove the undercoating and seam sealer. I had my tub primed (by the powder coater) with zinc rich powdercoat primer. This is an etching type of primer providing excellent protection against rust. Speak with the local powdercoater in your area. It's a great option.

Two issues that are a result of of media blasting are: 1. wavy warped panels from high pressure blasting (the operator needs to blast the exterior body panels at low pressure to remove paint etc. and avoid warping the panels) and higher pressure elsewhere. 2. your car will leak the blasting media for a long time. It seems like it never ends!

As for removing undercoating and seam sealer (that is why you are doing this right?) you have 2 choices 1. acid dip the tub or 2. countless hours with a torch and scrappers. I opted for hiring the unskilled-skilled labors to heat and scrape the undercoating and seam sealer from my tub. It will take 25-40 hours to torch and scrape this crap off, then you will find more that was missed! IMO well worth the effort, but a dirty nasty, smelly smoky job! By the way after the torching and scraping you want it blasted again. So, torch and scrape first!

Good luck!

Will

Andy, Here's what one racing prep business does:

"Stripped and Acid Dipped. Everything is removed from the car, including wiring harnesses, and the entire tub is submerged in a caustic solution to remove all adhesive, undercoating, seam sealer, body filler, and paint. If rust is present, a diluted acid solution is used to remove it. The process is neutralized with water, <i>and a coat of oil stops the chassis from rusting until the painting and body work are done.</i> This process is the most effective and cost-efficient method of reaching bare metal. With all sealers and coatings removed, the car is as light as it can be, and in addition, all hidden rust is uncovered and eliminated. <i>We highly recommend that the chassis be powderpainted after this process.</i> Cost is based on weight, $1.75 per pound."

http://www.autometricsmotorsports.com/products/911/index.htm#3-Transmission:

I think there is some good advice here and some things that will cause extra work. If you prime with a temporary primer, aren't you faced with the same problem getting it off for the good stuff? If you use the good stuff, you will get protection for a limited time, but not so liitle that you have to worry. Unless you just let the car sit. Therein lies its own problem; not monitoring the metal.

I vistited a well known 356 restoration shop last Fri. and the painter there leaves the metal bare until his first primer. He uses polyesther. Others here like epoxy for the first primer, but that is not a surfacing primer, i.e., for block sanding. The 356 painter states that etching primers are for non ferous metals. His opinion, not mine. BTW, the 356 shop is 20 blocks from the ocean, it's humid here too.

One thing you must do is metal prep before any priming. This entails washing the car with POR MetalPrep or similar and folowing with alcohol or one of the profeesional washes lie Dupont Prepsolve. If you monitor the metal and wash it down with the acidic metal prep, theorectically, you could leave the metal bare for months while working with the restoration.

My take is that each job is different, you have to go with what works in your situation. Here's my plan for the exterior: Hand strip and local blast rusty pitted area. Followed by metal prep and epoxy primer and move to the next area. When all stripping is done, prime all areaa with polyesther sanding primer and block out/repair as necessary. Seal and paint.

Me to. Im glad someone that knows what they are doing is going about this the same way. Im learning (mostly through repetition) as I go, and am in the process of doing the same thing. Ive never painted or prepped a car before, so this stuff is all new to me.

Everything is stripped to bare metal and the first coat of POR15 is going on a front fender as a trial this weekend. Plan is to work my way to the back of the car repeating this process as I go until the whole car is primed and filled. Ive got the POR body fillers and prepping material and will be shooting 'OMNI' epoxy primer on top of the POR.

thanks for the info people, i kind of like the idea of hand stripping (call me a weirdo if you will!) so as not to fill the car with crap, also im thinking its probably going to be a cheaper option, assuming i dont factor the labour cost into things. im now off to do a search on "POR15" to find out all about it!

Epoxy is an excellent choice for restorations, it has great adhesions characteristics and is excellent at corrosion protection. The great thing about epoxy is you can use polyester filler (Bondo) on top of it. This procedure id recommended by Porsche, Mercedes, Lexus, Jaguar and roll Royce.

Bryan

epoxy it is then! thanks blokes.

Bead blast/soda blast shell. Hit with etch & epoxy primer straight away. Then start thinking about repairs. Current thinking sways largely in favour of filling over a painted surface rather than bare metal.

POR 15 is good, although I'd rather stick with a manufacturer's complete sytem on external panels. Maybe POR shot tacky then wurth underseal on underguards and exterior floor?

Whatever it is..think rust rust rust, and decide what is best to stop it.

Good luck, Matt

Andy,

POR Products can be found at www.frost.co.uk

Cheers,

Tim.

And for those of us on this side of the Atlantic....they can be found at http://www.por15.com/ ;)

Good luck with your project and let us know what you do...I plan to strip a chassis in the upcoming months.

So it is true that sand blasting doesn't take off the undercoating? I thought it did?

Typical media blasting wont take off undercoating because the rubbery make-up of the coating absorbs the impact of the media.

There may be some high end equipment that is capable of this.

Are you thinking of the Zinc coating on the metal?

What do you classify as "typical"? Are you referring to the home type systems that are sold through places like Eastwood? Or the industrial strenght equipment?

Reason I ask is because I went on a tour of my local blasting/powder shop (http://www.ascoweb.com) and they claimed that their media blasters can run at such high pressures that they take off everything....so high that they can damage or bend the metal if they're not careful. Perhaps I should ask them if they can take off undercoating.....They do have media and pressures that are more delicate, especially for galvanized surfaces.

I would love to zinc coat the metal, however I believe that's exteremely expensive? What about a rust inhibiting powder coat that has some sort of zinc chromate?

My local blasting/powder shop can take the chassis directly from the media blaster to the powdercoating area within the hour. They routinely do government contracts which require rust inhibiting primers that withstand ocean/salt conditions so I would imagine that they could do a similar coating for an early 911.

REAL zinc chromate will kill you. They don't even use it in the aircraft industry anymore. I would steer clear, or use Zinc Oxide.

Nic,

Your local blaster sounds like a good, high end shop. How's the pricing?

Also, I purposely used the term "typical" for both home and business. Most businesses I've dealt with didn't quite have the industrial strength capability you speak of. Around here seems those caliber shops are after commercial business.

RickM et al. -
Just talked to the owner at American Stripping (my local industrial/military stripper and powdercoater....http://www.ascoweb.com). He gave some very useful information....which is as follows:

- Sandblasting may be able to take off undercoating if it is old and brittle. Chances are, if you can gouge it with your fingernail or screwdriver and the gouge stays, sandblasting will not be able to remove the undercoating. You also don't want to powdercoat with that undercoating on the car because the chassis has to sit in a 400 degree oven and it will drip off like molasses. If the undercoating is soft, you will need to remove it with hard labor scraping, heat guns, and chemicals.

- He cautioned that powdercoating is not the be all and end all...it will depend on the specific seam sealer and spot welds in the chassis. Since the chassis has to be in a 400 degree oven, it may affect the spot welds and loosen the seam sealer, possibly tweaking the alignment of the chassis.....usually determined on a case by case basis. If he looks at a car and determines that powdercoating is not the best idea, he suggests media blasting followed by conventional spray primer to protect the metal.

- While there is powder out there that may contain zinc, it is usually less than 50% which may not be enough to act as a galvanic couple and actually prevent corrosion in the body. What normally happens, is shops use a "zinc containing" powder, then coat with a powder top coat which essentially gives you two coats of powder which may not protect any more than two regular coats of powder.

- Overall cost estimate for sand blasting and powder coating the whole chassis inside and out (minus doors, roof, hood trunk and fenders) was in the range of $1200 to $1400.

Whew! I think I covered everything he said.....

more info!, i love it!

adomakin -
I think the information that you're looking for is....do you need to put a coating on the metal after sandblasting but before final finishing?

When I visited ASCo, he had a 1940's chassis that had been sandblasted and the metal still had that bare matte grey look...no rust! The owner said that as long as you keep your greasy fingers including salt and acid off the car, the metal will do fine. He cautioned that if you're going to be working on the car, it should be covered with something to prevent oxygen from getting to the surface.

Your primer depends on whether you want to cover up the primer later or take it off again before final finishing....I don't really have an answer for you but I would suggest a quick primer spray after sand blasting to protect the metal....you may also want to check out the myriad of "projects" at http://www.gunnarracing.com which go through the process of getting to bare metal, priming, painting, etc.

I have a like new ’74 914 body/chassis sitting in a trailer. It is still gun-metal gray with only a slight brown patina to the surface. I had it caustic stripped and then well washed in ’76 and have kept it all these years as a spare chassis for my original 914-6 CP/GT-2. As you can tell, I didn’t pay any attention to preserving it since it was just some replacement sheet metal. Living in Denver with thin air and little humidity the car is well preserved.

If I want to put this back in service as a hot-rod six, what is the best way to proceed? 911s have the same issues.

Best,
Grady

According to the research I've done, 2-part epoxy primers are the best choice if there will be a time lapse before painting. They are not as permeable as other primers. The Sherwin Williams website is a great resource and they will answer questions from newbies like us. I'd say email the professionals and do what they say.

David

Some questions I have pondered ?

1. Do late model sheet metal replacement parts already come galvanized so they are galvanized just like the later model cars were ?
2. If you use Epoxy primer do you have to be careful what compatible paint you put over it?
3. Is it true that once you acid dip, the car will keep rusting because you can never truly neutralise all the acid ?

I'll take a shot here:

1: The late model ('85) parts I've seen from the factory are galvanised and primed with a zinc based primer.
2: As mentioned by BG you should stick with same brand/same system materials.
3: The acid dip is used to remove the rust and then rinsed with water. I've never heard of a car continuing to rust when rinsed properly. That doesn't mean it can't happen. Others here can speak from exeriene.