Prep Work

[mcguijo]

Picture a TR3 body tub that has been completely stripped of everything; interior, fenders, wiring, etc. . naked. That is what I'm dealing with. I want to strip some areas to bare metal before I do any body work and later painting. In particular, I want to focus on areas that I don't want to hand sand; the engine bay, interior fire wall , and area where spare tire sits. After taking to bare metal I will put a single coat of epoxy primer on to keep from rusting. I've heard the horror stories about sand causing panel warping, etc. Although I'm sure it happens I just find it pretty hard to believe I'd have that problem with my home compressor (70 - 80 psi), portable siphon tank and 3/16' nozzle. So I want to sandblast forementioned areas. Here's my problem, the area I can sandblast and the shop where I could paint are 50 miles apart (in humid, central AL). I want to put a coat of epoxy primer on pretty soon after I get done blasting. However, the single coat of primer would have to be sprayed on outdoors. Any folks see any problems with this scenario? Should I do this outdoors? Is one coat of primer enough? What about thoughts on sandblasting?

Also, my experience has always been stripping small parts. Before I paint these after stripping I always spray them down with a heavy dose of brake cleaner. Should I clean the larger areas of the body tub with something after I sandblast and before I put on the primer?

 

[Andrew Mace]

Odds are you'll be ok sandblasting the areas you describe, as they'll all have angles, curves and/or embossed spots that strengthen the panels. Where sandblasting can cause real problems with warping is on broad, flatter panels such as fenders, doors, hood and trunk.

However you strip various panels, do get that primer on ASAP. Bits of rust can "flash over" a panel in a day or less under humid or other moist conditions.

Oh, and one more thing about the sandblasting: trust me when I say you'll NEVER get every last bit of sand out of various cavities and crevices. /ubbthreads/images/graemlins/shocked.gif

 

[DNK]

FInd out if therre is an auto dip tank in your area.That is if it is off the frame.
don

 

[dklawson]

Dipping is great if you can find or afford it. I did that with the bonnet of our GT6 and was very pleased.

Andrew beat me to it regarding the sandblasting. You should avoid sandblasting large flat panels. You'll be fine blasting parts and panels that have formed surfaces with bent edges, stiffening ridges, etc.

However, what I'd like to point out is that while sandblasting does a great job of removing paint, it can leave rust in cracks and crevices. If you already have rust under the paint, and if the rust has eaten deeply into the panel, sandblasting alone may not get all the little nuggets of rust removed. I suggest that when you've got the firewall and engine bay to bare metal you take the time to apply a phosphoric acid wash. The acid will slowly dissolve the rust, even the nuggets that sandblasting left behind. The object is to keep the metal wet until you get a dark grey coating, don't let it dry and go "white" on you. When it's all dark grey you hose the engine bay down, blow it off with compressed air, and wipe it with dry towels. A little bit of very very fine flash rust may form on the surface but this can usually be removed with prep-sol on a cotton rag. Once you've wiped it down with prep-sol and tacked the surface you can apply your primer knowing there's no rust below and that the phosphate (grey) coating provides an excellent surface promoting better paint adhesion.

If you're in a pinch for time, a well applied phosphate coating can be left for a couple of days without problem, even in high humidity, as long as you got through the prep-sol wipe down before painting. Our humidity is also high so I know the problem you face.

 

[AggieCPA]

There is a company that dips car bodies and does the dip coating in that part of the country - I just can't think of the name right now. If I was going to strip it down that far there is NO question in my mind that redi-coating is the way to go.

 

[Alan_Myers]

Hi,

Hmmm. I'm afraid I have to disagree with a few points that have been made.

I have avoided dipping because I've seen too many pretty new paint jobs ruined when a bit of the chemicals later seeped out of hiding in a nook or seam or cranny! I've even seen this happen a year or two or three later.

On the other hand, I haven't even considered dipping parts in years (decades actually) for this reason, and modern dippers might have come up with effective solutions for that all-too-common problem. Perhaps they really, thoroughly neutralize the chemicals now. I don't know. Ask lots of questions if you consider it!

There is a process called soda blasting that would be my first choice. It avoids warpage, but cleans off the old paint quickly. I would send the car out for this, not try to do it myself.

My 7 hp compressor is nowhere near powerful enough for a true pressure-fed media blaster that's essential to this large a job, plus proper protective gear and breathing apparatus are expensive. Note: I do now use that compressor with a small pressure fed blaster, for frame work and with a blasting cabinet for parts up to the size of a wheel. Several times in the distant past I've done an entire car with a small compressor and siphon blaster and can tell you that's a long, long, long, dirty process.

Another media blasting method uses walnut shells or plastic beads as the primary medium, with a bit of harder media mixed in to effectively remove any rust. Done right, with minimal carbide or other hard media mixed in, this will also avoid warpage to a large degree.

Alternatively, use paint stripper on the large, relatively flat panels, wash it off well, then media blast the edges and more complex areas that aren't a warpage concern, and only lightly blast the broad areas.

Working out of doors with media blasting is a bad idea in most climates because flash rust will form long before you have a chance to get paint on the car. Maybe you could get by with that in Arizona, New Mexico or as I did in Colorado, years ago. 15% humidity there. But, your neighbors will hate you.

And, I don't know about painting out of doors, either. There is dust and moisture to be concerned about, of course, and the neighbors. What are your state laws like? I know here in Calif. I'd face a hefty fine for doing that!

Most automotive media blasting shops are set up to immediately spray on a coat of primer. A lot of folks now use some sort of epoxy primer, as a base coat, just as you are considering. You also need special breathing apparatus to spray this stuff. Subsequent coats of other types of primers will be used later, in the process of finishing the car and prepping for final top coats.

By the way, right after the initial epoxy primer many top pros do a skim coat of especially thin bondo over the entire car and use long sanding boards to take most of it back off. This perfectly levels surfaces and finishes edges before additional primers and top coats are put on. Believe me, I would bet your car has far more surface warpage and variations than you ever realized, even when new and fresh from the factory.

Oh, and never use actual sand for blasting. Fine particles of it that are inhaled will lead to an illness called "silicosis". You don't want that!

IMHO, media blasting is the most effective method of removing rust and prepping the surface for new paint, with the least concerns about something coming back to haunt you later. A little "tooth" on the surface is formed in the process, which is just about perfect for best primer adhesion. Little or no hand sanding is needed. I haven't used it yet, so don't know if soda blasting also provides that sort of surface, but I do know it has great cleaning qualities, removing grease and other contaminants that can keep paint from sticking. Other types of media blasting are less effective at removing oils and greases, so some wipe down to prep the bare metal is usually needed, before applying paint. I too use brake cleaner in some instances. Acetone and lacquer thinner are good for some types of paints. The primer you choose should have specifics noted on it, what to use prepping bare metal.

Honestly, I'd suggest looking for a media blasting shop near you, talking with them and at least getting a quote. I suspect you will find it considerably cheaper than properly getting set up with a large compressor, pressure fed blaster, the right media, effective oil and water seperators for the compressor and the mandatory safety equipment, plus the painting equipment and breathing apparatus to work with the epoxy primer.

 

[AggieCPA]

[ QUOTE ]
Hi,

Hmmm. I'm afraid I have to disagree with a few points that have been made.


[/ QUOTE ]

I think that was a legitimate concern at one time, but from all the research I've done it doesn't apply to the process where they use today.

I don't see how a person can get better coverage than dipping the entire body in primer and having all surfaces covered with primer - even the surfaces that won't get painted.

 

[mcguijo]

Firstly, I think soda blasting has been oversold. I paid (alot) to have it done on a couple of fenders and wasn't that impressed. It does a good job taking off exterior paint. Does a moderate job removing factory primer. Does nothing to remove rust.

As for blasting outside; I have no legal limitations and the property is 40 acres. Neighbors be damned! I also can't see dust being a problem. Good ole' Alabama clay in these parts. Maybe an occassional bug. But wouldn't the primer be blocked before painting anyway? Anyway, that's why I'm only planning on putting on a single coat of primer. Basically I want to stabalize the blasting work to keep from rusting. This will allow me to move the tub the 50 miles to the paint booth. I'm sure the paint guys will lightly scuff the primer, reprime, rescuff, and reprime before painting. Anyway, we do have high humidity in these parts...50% at present. So unless, you're doing your prepwork in a vacuum, I'd guess there will always be slight rust. .even with the experts. Keep in mind that ALL of the restoration shops in these parts do their paint stripping in one building and move the car to the paint booth. I don't see what I'm doing as much different. As soon as I get the metal cleaned (using technique suggested above), the primer is going on.

 

[swift6]

[ QUOTE ]
By the way, right after the initial epoxy primer many top pros do a skim coat of especially thin bondo over the entire car and use long sanding boards to take most of it back off. This perfectly levels surfaces and finishes edges before additional primers and top coats are put on. Believe me, I would bet your car has far more surface warpage and variations than you ever realized, even when new and fresh from the factory.

[/ QUOTE ]

My body guy uses what I assume ( I know, dangerous) is a brand name product called 'guide coat'. Or maybe thats his own thing. Regardless, it's two different colors of primer (I seem to remember the traditional gray and sort of a light blue color) and when he does the first sand of the, body, section, panel etc... the blue (top coat) is sanded away revealing the gray. Wherever there is blue left are the low points that either need some manipulation, lead or other filler. This is also a repeated process, not just a one time deal, until there are no more low spots.

He also told me that media blasting does not leave the best finish for adhesion. It tends to flatten the tooth of the metal. He DA's everything that has been blasted to get the tooth back. Since he is a professional who holds many factory authorized finish certifications, I tend to take his word on the stuff. It could also just be a matter of opinion though.

/ubbthreads/images/graemlins/cheers.gif

 

[Guest]

Speaking of body prep, at the VTR one of the best looking TR4's I have ever seen (looked like the 97K at B-J) just made me smile. Finished to perfection, perfect interior, flawless paint, an engine you could have your breakfast on. Till I got down on my knees and saw bubbling on one rocker panel. Man, I think I would go shoot myself, or my body man at least!

It is soooo hard to get these things right. What a pity.



Bill

 

[Bugeye58]

Shawn, "guide coat" is merely the spraying of a contrasting color over the primer, and then sanding as you mentioned. There's no brand name associated with it. I usually use a rattle can for guide coat, in whatever color is handy, as it's a good way to get rid of cans with little paint left in them.
Nonetheless, it's the best way to insure that the surface is truly flat.
Jeff

 

[KenASh]

Hi PrepWork,

I have lots of experience with this as I totally restored my 64 1/2 Mustang. If you don't already know, Eastwood has a huge listing of body prep materials. Living in the mid-atlantic area near the coast, humidity is a real issue. After blasting, by what ever means, and for new panels, I used a product with great success called metal wash purchased from www.eastwood.com. First it gives several days and perhaps a few weeks of protection against flash rust. It is a powder that is mixed with water (go figure) and is simply wiped on the panel. I used a spray bottle and rag. Furthermore, it keeps forever, it seems. Also, if memory serves me well, if leaves a base condusive to the application of an "E" coat or etching primer. It is really great stuff!

 

[bobh]

10 or 12 years ago I had some body parts dipped by a company in Mount Juliet Tennessee. I don't know if they are still in business, but I can try to find out.
They explained the method as sort of a reverse electro plating. Where the body part was the anode. Only rust was supposed to be released from the body part. It was a very thorough cleaning of the parts. I had them do the same for a Ford Flathead engine block. It came out looking like a fresh casting. Inside and out.
Blasting with just about any type of media can warp a panel. When you blast, contact between the media and the panel generates heat. This probably contributes some to the warping. Pressure settings also have to be matched to the media and the material. As Alan mentioned there are many options for the media. Each option has it's own characteristics. Some are more agreesive than others. In general this has to do with hardness and shape. A very hard abrasive with sharp corners will be very aggressive. Where as a softer media will be easier on the material.
If you would like for me to try and find the name and number of the place in Tenn send me a PM. Mt Juliet is about 120 miles fron Huntsville which is where I'm locted.
BOBH

 

[MDCanaday]

If you have a bare body tub you can certianly sandblast a lot of it.But NEVER, EVER blast an exterior body panel.Pans, firewalls fender aprons, ect but, put duct tape over the cowl and saddle panels so your guy doesn't do what they all will.......screw it up!!! My hard learned opinion is get it done with media if its not too rusty.Media does NOT remove rust,just paint.Then you can finish of the rust with a small blaster you described. It is critical to get a metal etch primer on this white steel in the first hour. Plan ahead so this can get done.NEVER touch white steel without a cotton glove(unless you like rusty handprints that come up in 6 months)Read the directions,most etch type primes are time sensitive to the next coat.Be ready to go all the way to color, this includes seamsealers ect. Good help is a big plus(2 man job).Good luck!!
MD(mad dog)

 

[Jon80spit]

A lot of good advice here. I use paint stripper for all flat surfaces, then follow up with a scotch pad on my die grinders. Everything else blasted or sanded with an aggressive scotch bright pad in the die grinder. I use black diamond (carborundum I think)for rusty/painted steel. Use walnut shells for aluminum and shot for iron castings. Degreas and de-wax before hand. Do not wipe down bare metal with rags or paper towels unless you are sanding next. Fibers will get caught and when you prime, will form wicks to start corrosion. A sharp media such as black diamond will allow you to get in and out faster before you heat up the metal, just watch blasting through. Dull or the wrong media forces you to hold it on longer, heating it up more.
Blast and paint right away. Paint it right where you blast. If you can't do this in one session, do it in sections. I did a tube steel champ airframe three feet at a time. Blast three feet and paint it. Next day blast three more and paint. I keep stripper or other chemicals away from seams. Have seen too many paint problems there.
For guide coat, I use lacquer. Epoxy takes too long to dry. Spray a mist coat and it dries very fast. After sanding, you can remove it with lacquer thinner.
Lastly, wear a head band and long sleave shirt to keep from sweating on the metal.