Frame refinishing…

[John A.]

I have a few questions regarding the restoration of frames that have become rusty over the years. It’s inevitable that the steel frames will begin rusting at some point in their life – some sooner than others!!! So, what’s the NCRS position on the different restoration practices – ie… de rusting and the re application of a rust inhibitor? Is media blasting preferred over chemical stripping? Are the rust inhibiting systems (POR15) and epoxy topcoats acceptable…??? or, is the position that once a frame is stripped, OEM asphalt based coating are the only coating viewed as correct and acceptable???

Got any product recommendations?

Thanks

[Jack H.]

From a judging standpoint....

it's all a matter of cosmetics. If the final job 'looks' to the naked eye like a factory fresh frame produced in the era, then it 'flys' on the judging field.

Some blast/clean their frames, and use a form of filler (leading, epoxy, Etc.) to remove pit on those surfaces that'll be visible once the body is in place to generate that freshly extruded surface texture appearance, then paint over.

Some use an epoxy based paint (DP-90) that's thick and will naturally flow/fill minor surface pit by itself.

Some have the entire frame powder coated to FORCE a uniform surface appearance and thwart further frame deterioration.

Bear in mind that powder coating will tend to look 'artificial' to the trained eye as it's VERY thick compared to traditional painting methods. Also, it can be a problem for those fasteners intended to connect to the frame (build-up may generate interference fit by reducing the ID of drilled/tapped holes) as well as inhibiting physical contact at various points intended to serve as electrical contacts for chassis grounding.

Others, have powder coated with selective masking to thwart interference problems and then come back over the powder coat with the original asphalt paint to dull out the final appearance.

This is an area where the 'artform' portion of restoration/preservation governs. There's no 'correct' answer as to how to do it, just a spectrum of approaches. The 'right' way depends on the specifics of your frame's condition, your objectives with the car (primarily a driver, primarily a factory concours show car, Etc.), your wallet, and personal pride in the restoration job....

[Chuck S.]

Re: Frame refinishing…

John, NCRS takes no direct "position" on any methods used to restore a Corvette. NCRS only judges Corvettes based on their APPEARANCE compared to the standard of how it appeared when it was delivered new from the selling dealer. Every member has his/her own opinions on the methods used to restore a Corvette.

Any way that you can obtain the standard without introducing some visual side effect that wasn't there when the factory did it is fine with NCRS. For example, a restored car could receive point deductions if paint is too glossy, film thickness is obviously greater than original, paint has coarse non-original orange peel, and in the case of frames, if runs are in the wrong direction (C3s for sure, others?).

I had my frame blasted, and this was the method of choice until recently. If I do another one, commercial chemical dipping would be preferable if I can be convinced that the technique will not obliterate the stamps or weaken the weld joints. In either case, you should be extra careful to refinish the inside of the frame rails and cross members. Blasting may leave some, maybe most, of the original paint inside the frame members, but chemical dipping will leave absolutely NO PROTECTION. You can get good inside coverage if you apply multiple passes carefully with an undercoating gun using a variety of tubing lengths.

As far as materials, you can use any paint you like so long as you end up with a finish that "LOOKS" like the original paint finish on the frame. I would probably coat the inside of the frame with POR15; nobody is going to judge the INSIDE of your frame, but I would make sure to clean up any outside runs and drips before it cured. POR15 dries rock-hard and will be very difficult to remove after it cures. I wouldn't use it on the outside of the frame; it is not required on a pampered collector car, adds a lot of non-original appearing film thickness, and isn't UV resistant without a topcoat. I would prime the outside of the frame with PPG DPLF90, and top coat that with acrylic enamel flattened to the proper frame gloss. Be advised that the asphalt based paint was not used on C3s; your profile says you own a 69.

[John A.]

Re: Frame refinishing…

Chuck and Jack,

Good info… Several points well taken. Chemical stripping sounds good, but I’m not sure it’s feasible because of the availability in my area. I’ll have to look further into it. Treating rusty areas with a rust encapsulator makes sense. I guess I’ll have to further evaluate the DP90 vs. POR15 for the exterior of the frame. If a topcoat is applied, I don’t see why POR15 wouldn’t be preferred – based on superior rust preventative properties.

Two more questions, when did they stop using the asphalt based coating? The Judging guide calls it out. What did they use in its place? Which way should the runs be? … Weren’t they were dipped upside-down? (Sorry - make it three!!)

Thanks

[Chuck S.]

Re: Frame refinishing…

Your TIM&JG says 69s have asphalt based frame paint??? Asphalt based frame paint was used on midyears. I always thought it ended in 67, but I am DEFINITELY SURE it ended before 70. Maybe I have been blissfully unaware of reality for more than a decade; it wouldn't be the first time.

Actually, removing the rust rather than encapsulating it makes the most sense. Rust scale may be hiding areas that need structural repair, and it won't do to find it out after the car is back together. POR15 is a great product, but I would just as soon not put the advertising copy to the ultimate test to see if it can contain pre-existing rust. As I said before, POR15 is not UV resistant, so ideally, it should be top coated unless it's in the dark. It can be argued that the frame isn't going to see any UV, but I don't understand the need for superior rust prevention...are you going to drive this car in rain, ice, and snow (salt)? Anyway, you are the one that has to be pleased...use whatever you think is right.

GM used a black enamel-like paint on C3s, and the frames weren't dipped...they were "hosed" in the upside down position over a pit. I don't know if some enterprising vendor is selling a "genuine, authentic C3 frame paint" these days, but I had a bad experience with something claimed as the genuine article; it still wasn't dry after SEVERAL days. That was ten years ago; maybe it would be dry by now. I concluded it had to be applied HOT to cure properly, and cleaned off the entire mess with mineral spirits.

[John A.]

Re: Frame refinishing¡K

Chuck,

Thanks for the feed back ¡V yep! Page 83 ¡§An asphalt-based coating was used¡¨ ¡K right after the ¡§semi flat to semi gloss statement¡¨ .. doesn¡¦t make much sense now that I think about it. More investigation warranted based on your comments¡K. The idea of a coating that may not dry doesn¡¦t excite me much ƒº

Good point on the POR15 ¡V I don¡¦t think the car will see much rain. But here in the south east, 100% humidity is common and I¡¦ve seen parts that I have blasted clean accumulate surface rust in a matter of weeks just sitting on the garage bench. Even after a clear coat... Maybe I¡¦ll do some testing before I commit to a product.

Thanks again

[Dick W.]

Re: Frame refinishing…

Have had good results on several frames by sandblasting to remove rust. You can put duct tape over VIN to protect it. I would blow all sand out, then use a phosphate wash on the bare steel. At that time we would prime with PPG DP-90. For rust pitting, I would use a heavy built PPG primer/surfacer and sand it down. Any time that we hit bare metal we would again spray that area with DP-90. Would do that until the frame was smooth, but being careful not to get too heavy a built of primer/surfacer. Would then seal frame with a light coat of reduced DP-90. Came back over with a topcoat of PPG Deltron black flattened to an eggshell gloss. Did several cars that were Duntov and Bloomington Gold and took no hits on the finish. Also did a '72 body on frame restoration on a driver over 10 years ago. Frame still looks good after several NCRS Road Tours.

Most of all, as Bill Williamson has said in several posts, stay with one manufacturer of finishes. All urethanes and epoxies ain't necessarily compatable. And please use Respiratory Protection and adequate ventilation. All modern finishes are TOXIC. Take care of your lungs. They are the last set that you will get.

[John A.]

Re: Frame refinishing…

Dick,

Thanks for the sound advice!!!

John

[John A.]

Re: Frame refinishing…

Dick,

One more question - which product of the Deltron line did you use...2000, Universal, or the Urethane???

Thanks

[Chuck S.]

Re: Frame refinishing…

John, of those three, only Deltron acrylic urethane (DAU, formerly known as acrylic enamel) can be used without clear coat. PPG Deltron branded products DBC (2000, base color) and DBU (BC/CC system) must be clearcoated. I suspect Dick was recommending DAU for your frame.

[John A.]

Re: Frame refinishing…

Thanks Chuck!