1963 FHC – Corrosion Protection

Posted by newhillgarage ⋅ July 2, 2020

Months ago, I started thinking about having the body shell media blasted. That led to me thinking about what to do right after it was blasted. In general, the car was in stable condition with original paint or newish primer (that I applied 15 years ago). I knew that as soon as I had the steel body media blasted, at some level, maybe microscopic initially, that rust would begin to form. What to do?

To digress for a minute, most modern automotive finish systems, regardless of manufacturer, have Technical Data Sheets (TDS) associated with each product. TDS have a generic format. Among many pieces of information on the TDS, it lists the acceptable “substrates” which is a fancy word for what the product is being applied to, and “topcoats” which is what you will apply next. Another typical parameter is “recoat windows”. In general, a recoat window is the time that may elapse before you apply the next product, i.e. the topcoat. Also in general, the recoat window, which is generally measured in hours, not days, can be “reset” if you sand the surface. Here is a Recoatability statement for ChromaPremier Sealer 42400:

When recoating ChromaPremier® 42400S™ / 42410S™ / 42440S™ / 42470S™ / 2K Premier Sealer with itself, sanding (P400DA or P500 grit dry or wet) is required if the sealer has been allowed to dry more than 16 hours. For best performance Cromax® Pro should be applied over ChromaPremier® Sealers in 1 hour or less.

To digress even further, if you recoat within the time limit, the new product will chemically bond with the previous product, as it has not had time to fully cure and the molecular chains will intermix. If you defer and use sanding, you get a “mechanical bond”, which means the new product locks in with the sanding scratches from the previous product, suitably sanded. With modern products, I think the chemical bond is somewhat better but a mechanical bond is just fine if done correctly. If you want to see what happens if the sanding is not done correctly, just look at the aftermarket sprayed bedliner applied to my Ford F150! But that’s another story.

My dilema as a solo guy painting a car is meeting the Recoat requirements. Sanding in itself is not a problem and is inevitable for the exterior of the car. But what about the interior and the underside. Unlike the exterior, the interior and underside represent a maze of convoluted surfaces, not at all easy to sand. One solution is to be prepared to shoot your primer, sealer, basecoat, and clearcoat all in one session, within a short time of the car being media blasted. Not going to happen for poor pitiful me. I posed this dilema to my Axalta Tech Rep and he came back with a solution I can live with. He said apply 2 products to the bare blasted metal first. Then I could wait to do the rest. In the Axalta world of products, he suggested 5717S and 5718S.

So what are these products? First of all, I would call them “washes”, as they are chemical liquids that can be brushed on, sponged on, or sprayed on. The TDS description of 5717S is:

DESCRIPTION
An acidic concentrate for the cleaning and conditioning of ferrous (iron-containing) metals before painting. Effectively removes rust and corrosion, inhibits the formation of rust under paint, and etches the metal to improve adhesion.

APPLICATION
 Apply the mixture with brush or sponge. Scrub the wet metal with a scuff pad or brush to remove rust and corrosion.
 The metal must be kept wet during scrubbing.
 While metal is still wet, rinse thoroughly with clean water. If drying begins before rinsing, re-wet with 5717S™ Metal Conditioner and rinse with clean water.

Not too bad. And then we move on to 5718S:

DESCRIPTION
A 6.5 lb./gal (780 g/l) VOC compliant, non-flammable, phosphoric, acid-based conversion coating that produces a uniform zinc phosphate coating on steel and galvanized steel surfaces. The zinc phosphate coating formed on the metal surface offers the best possible substrate for paint system adhesion and corrosion resistance.

APPLICATION
 Apply 5718S™ without dilution to the surface.
 Lightly scrub the wet metal with a scuff pad before rinsing. Rinse with water.
 If surface dries completely before rinsing, re-wet with 5718S™.

Most importantly and as confirmed by the Tech Rep, once you do these 2 steps there are no timeframe limits and no sanding requirements before doing the next step, which will be applying a primer. FYI, the “no further sanding” makes additional sense, as these products do little or nothing to the “as blasted” surface texture, ensuring a good mechanical bite.

So I did it. Later in the same day that the blasters were here, I did the above process. It’s a little (hell, it’s very) scary to be rinsing your precious blasted metal with water. I had done this previously on another job and was prepared for the resulting “look” which could be best described as a bad spray tan, poorly applied! In the pictures below, I’m sure that to the uninitiated it looks just like a bad case of surface rust. But I believe in the science, in this case the chemistry. This will give me time to do any metalwork and application of filler. As noted in my previous article, this car is a gift as there is almost no rust repair to be made, just correction of some previous bodges in the floors and firewall.