After finishing the interior, I decided to adjust the order of work on Nonna. First, we did dry ice blasting on the underbody, it’s much worse than we expected. It seems that tropical islands do not mean pure dryness, but also cruel corrosion. So we have to disassemble the front and rear axles and do the engine work at the same time. In this way, we can paint the body first and wait for the paint to shrink while working on the underbody.
I had only painted Persian Kitty before, and I would rate that job a B-, though the average painter would be D in my opinion. Even though I am still a beginner in terms of experience, that was two years ago, I think my theoretical knowledge has improved a lot. While getting along with Persian Kitty in the past two years, I often reflected on my mistakes in the paint job, and kept an eye out for new techniques and tools, so I guess we will definitely improve this time.
To be honest, the moment I finished painting Persian Kitty, I had a hunch that I would never paint a car again. So I imagined that my sons would be proud to speak out that their dad painted that blue car they were sitting in, instead of a bunch of cars. Because painting is a very time-consuming job, I squeezed in time to paint Persian Kitty when my kids were very young, and I thought I would never have such an opportunity again. Oh dear, now the kids are in kindergarten and are very well behaved, I am free again. See, I am a person who does not keep words, and I always break some of my own vows.
An important opportunity is that Nonna is easier to paint than Persian Kitty, she is silver. Silver reflects a lot of light, so there is not much mirror reflection. Persian Kitty’s Azurite Blue is almost black in the shadows, the mirror reflection is very obvious. In that case, all the flaws and phantom waves will show, so I am unlikely to lose too much with Nonna. I have also mentioned repeatedly that Nonna is used to commemorate my grandma, so I would do the work myself as much as possible.
Revision
First, a revision on Persian Kitty’s past work. Reflection about this started before we were done, but my memory isn’t great. Fortunately, I also took notes on this at the time, so I can get some tips. The older article “Restoration: Paintwork for Persian Kitty” is more about how to learn to paint properly. During the past ownership, I also discovered further changes in the paint, which are also very valuable.
Sanding marks
Persian Kitty was painted in February 2022. Then one day in June, I first found sanding marks on the hood, and then they also appeared on the trunk lid. Obviously, these had not appeared when we thought the polishing was completed. These sanding marks are caused by the shrinkage of the clear coat, and I would attribute it to 3 following reasons.
First, I used the Festool dry sanding system throughout the process. It’s a fashionable studio tool, the efficient one, and I almost stupidly set myself some kind of deadline. For example, at the beginning I set the time budget to 1 month, and I always tried to complete the daily preset tasks as soon as possible, even if it took us 3 months in the end. A dry sander can sand quickly, but its unique mesh sandpaper can cause some damage to the sheet metal. Some of the sandpaper marks that appear in the end are circular, which is left by the dry sander.
Then, the clearcoat had not fully shrunk before polishing. We sprayed the paint on a -10 °C day and only did some baking without leaving it in the sun to dry. This was again due to my impatience and wanting to finish the polishing and the subsequent work sooner. When I was at McPherson College, our school projects often took months to shrink before polishing, and I completely forgot about it. So the clearcoat continued to shrink after polishing was completed, and when summer came, the paint changed drastically under the baking of the sun, showing the sanding marks.
Finally, too much material was piled on. Persian Kitty has quite a bit of original paint, so I did my best to replicate the thickness of the factory paint, which is 120 mm horizontally and 100 mm vertically. To achieve this goal, I did not use traditional fillers, but metal repair agents that I had never tried before. And I reduced the use of epoxy primers and used rust converters to cover the exposed metal. Later, when I got more exposure to these two Wurth materials, I found that it was not a good idea to use them in the paint job. You should reduce the number of materials and test new materials in advance, because every material may shrink.
Phantom waves
This is a term I learned from Linear Blocking Tools. Phantom waves are waves that are produced when your eyes move across the panel, which are obvious at some angles and absent at others. It is a greater visual obstruction than sanding marks, especially on dark-colored bodies. They are particularly obvious when observing the side at a large angle. I would also attribute this problem to 3 following reasons.
The first is the disregard for fillers. In order to achieve factory thickness, I almost sanded off all the paint, and then gave up any fillers, but rough metal repair compounds. In fact, few people can completely refuse fillers, and they are critical for forming a smooth surface. We also performed PDR before sanding and thought that the dents were actually gone. The fact is that the paint in the dents is compressed, and when they are removed, a high point is formed in the sheet metal below. So after the panel is heated to 60 °C by the sun, these high points appear.
The second is rough sanding. I believe in the long Festool dry sander and believe that it can sand a smooth surface. So I completely ignored wet sanding, even when polishing. Although I used a long block before painting, vibrating sanding did not help much for leveling. As for polishing, I think I used the dry sander to violently scratch many gullies in the paint surface with 1200 grit sandpaper, and they could not be repaired by finer sandpaper. As for the reason, I will talk about it next.
The third is too thin clear coat. Still pursuing factory thickness, I only painted PPG D8122 CERAMICLEAR® once to avoid too thick varnish, we painted at least twice on other cars. This clear coat is very strong to sand down the orange peel, so I decided to use a dry sander. But later I found that the clear coat was too thin and I couldn’t remove much with the dry sander. So when I realized that the paint surface had become uneven due to the dry sander, it was too late and there was no more thickness to use for sanding.
Maintainability
Persian Kitty’s paint has shown some problems in the past two years, some of which are maintainable and some are not.
D8122 CERAMICLEAR® is PPG’s top-of-the-line product, and it has an impressively high resistance to scratches—depending on how you look at it. When you scratch it with a key, “nothing happens.” But when you wipe it with a dirty film cloth, it leaves swirls. So it can only resist serious damage, not small scratches. When the key is scratched, it also leaves a mark, not that nothing really happens. We live in a practical world, and swirls are not a problem for most people. But all the cars in this school live in another world, they are unlikely to be scratched by any malicious objects for the rest of their lives. So, swirl are a more realistic enemy, especialy on dark paints.
Excellent scratch resistance makes D8122 bulletproof to aggressive abrasion, including sandpaper. Polishing D8122 must face the fact that it is difficult to wet sand, and ordinary #1200 wet sandpaper is inefficient. This is the direct reason why I used a dry sander and caused some trouble. If you plan to retain orange peel and only sand some dirty spots to a limited extent, D8122 is a good choice. For us, it makes swirl removal maintenance difficult, and we are not worried about scratching with more serious things, so I prefer some more sandable varnish. The choice is PPG D894. This product is not top of the line but is more than adequate for our purposes, can be easily buffed to a shine and maintained in this way.
Outlook
The above is a reflection on the three main problems of Persian Kitty’s paint. I have been imagining how to do it better for long. For Nonna’s paint, we evaluated it as soon as we got the car. There are 5 panels with original paint, including the hood, the two doors on the driver’s side and the rear fenders, and the roof. At first, we decided to keep the original paint and try to increase the area of ​​original paint. The approach was to find a car of the same color and period to donate some sheet panels. Only the rear fender is not removable, so we can get at most 10 of the 11 panels. For this purpose, a low-mileage 1993 300 SEL was purchased, which was 3 months different from Nonna. But we found 3 reasons to give up the original paint.
Rust spots
Like all cars, Nonna’s hood has a lot of paint peeling from stone impacts, but the difference is that even the smallest holes have caused corrosion underneath. This is probably the power of the sea next to where it lived in last 30 year. Each hole forms a circle of peel off, and these holes only will get bigger and bigger. The entire hood is covered with these circular rust, so the original paint of the hood cannot be preserved. Similar rust appeared on the side where the original paint was. The sea water penetrated the clear coat and the base coat and E-coat, then the zinc on steel, and the rust was formed directly on the metal.
Uneven metallic grains
Before I got out the paint meter, our painter thought there was no original paint at all, his reason was that the silver metallic grains did not look like the Mercedes-Benz quality he imagined. The grains were sparse in some places and very dense in others. I am not very sensitive to this, and I guess the average S-Class user is also. But if you look closely, he is right. This is not a very important point, and we wouldn’t make any pretentious claims that we would exceed factory standards, but it is an interesting observation.
Cracked clearcoat
Although the low-mileage donor we acquired had the original painted doors and fenders we need, which meant we could assemble 10 of the 11 panels with original paint, only one rear fender was non-removable. But the donor’s clearcoat had a lot of tiny cracks as the car was not properly preserved. Cracked clear coat happens on other colors too, but never so noticeable on the metallic silver unless you are standing 5 meters away. This distance is enough for most people, but dear, I am responsible for washing her. We tried lightly sanding the original clear coat to remove these cracks, but they have sadly seeped through to the bottom. There is no point in fitting these panels to the Nonna.
The conclusion was to repaint Nonna’s whole body for consistency. Since there is nearly half original paint, this didn’t look like a difficult job. The most important methodology for this job was: no time limits. In previous interior works I still followed my plan, but here there was no timeline to rush us, and there were too many unknowns under the paint. No one really knows how long it will take to work on which cars, so if you give such a task to someone else, you should pay more than you should for a good result. The advantage of working in person is that you know where the time goes and how much you have done.