Let's Talk About Paint

Paint!

You know, that stuff you put on a surface to make it look nice and keep it from degrading under the harsh effects of UV, moisture, and so on. It's a topic I think that most would-be restorers take for granted. I mean sure, everyone knows that they'll have to decide what to do with their project's body panels. You could DIY this or ship your body out to a professional for treatment. But I'm not talking about that kind of paint. 

No, I'm referring instead to the little jobs, or the jobs you are sort of expected to do yourself as part of a restoration project. There are many of these little jobs and, as I'm discovering, they all have their unique requirements in order to build something that lasts. 

As one of two of you will know (look, I'm being honest. Almost no one will read this, so it's really just a vanity project for myself) I am in the process of restoring some of the underbits. You know, axle casings, differential housings, etc. etc. etc. Primarily, stuff that will live under the vehicle and will be painted a semigloss black.

The reader will know by now that I am a novice. As in, I have some rudimentary skills, but nothing that could be called 'expertise' or 'experience.' I'm essentially starting from scratch. Until now, my exposure to paint was the rattle cans one buys from the big-box store or the gallon jugs one uses to paint one's home. This is... ironically, probably enough actually. The previous owner of Duffy painted most of the body panels with house paint. 

But, spend enough time poking around some of the Internet and you come across new and exciting (and expensive) products that seem to make promises of durability, longevity, or specialized use in situations where the surface to be painted is less-than-ideal. Because, let's remember here, when we talk about paint and coatings we're also talking about the substrate that it's painted on. 

If you, like me, have a rubbermaid full of parts, they will likely be in various shapes and sizes and various states of (dis)repair. There will probably be some surface rust or old paint to remove. 

The decision, then, about what to do becomes quite interesting and, I've learnt, complicated as well. Everyone wants a relatively clean and shiny project when complete, or at least one that will be durable. This, then, leads one down the rabbit hole of surface preparation and paint selection. 

Surface Prep

Most paints you can buy are excellent at adhering to bare metal, i.e. metal that is absolutely clean, free of grease and old paint, and oxidization. Some paints, however, are perhaps more tolerant of less-than-ideal surfaces, and one can pay more money to buy these coatings at the expense of not having to prepare the surface as well.

Therefore, the first decision to be made when contemplating restoration is whether or not to return the parts in question to bare metal. 

This is not as straightforward as it sounds! The primary factors at play are, as with anything else in the restoration game, cost and time:

• You could, for example hand-sand every part down to bare metal. This is probably not a recipe for success for most people. 

• You could mechanically remove rust and old paint by e.g. using a wire wheel on an angle grinder or, in the extreme case, sandblast the parts you want to paint to fully get back to bare metal. 

• You could use commercially-available paint strippers.

• You could, if the part has a good coating on it already, just scuff it up and topcoat it with something to make it look nice.

Complicating things is the nature of the metal underneath. Steel is used everywhere, so most paint formulations generally do very well when applied to bare steel, particularly when paired with an etch primer. Aluminum, or alloys such as birmabright, require a little more care when painting. Galvanized steel requires even more preparation, as paints will not stick to galvanized metal if it has oxidized. And then you have to decide if you're going to brush-coat your parts or spray them. Therefore, many decisions need to be made along the way. How much work are you going to put into your part in order to prepare it for paint?

Paint Options

Spend any amount of time on the Internet and you will start to get some recommendations on coatings. Steel-It is a popular choice, as are the POR-15 line of paints. My local Lordco has a bunch of rattle cans of Duplicolor which would also work pretty well. All of these coatings have different strengths and weaknesses. 

Steel-It is a paint with steel in the coating itself. It's meant for applications where you want to have a hard coating and it seems to be a pretty good choice if you want to  weld the part afterwards. It comes in spray format and it seems to look pretty nice. It's an expensive coating: a single rattle can is $50. I think you just need one application (probably two coats?) of Steel-it to work effectively. 

POR-15 is a grandaddy of coatings in the automotive world. As the name implies, you can paint right over surface (not loose) rust and it will convert it to a stable oxide that prevents rust from spreading underneath your paint finish. POR-15 is not UV-stable, however, so if the application involves any exposure to sunlight you will have to topcoat it. They have a whole system of cleaners / degreasers, metal prep, and coatings that all work together. POR-15, like Steel-It, is also expensive, especially if you combine all the steps you need. But it's really 'dense' paint that works very well. 

Duplicolor is a household name because you have probably used their products before if you've bought a rattle can from your local hardware store. It seems to be pretty good paint, and it's much less expensive than the other two. Sprayable and relatively cheap -- a pretty good combo! Is it as durable, though? 

Once you've selected your 'system,' then you have decide about primers: etch prime is not the same as high-build primer. Some coatings don't need a primer coat at all. POR-15 is a direct-to-metal paint.

On to The Work!

I am working on getting my axles ready to go under the new chassis that I've ordered. I'm not painting galvanized steel (for example), so this job should be pretty straightforward. Of course, I did have to decide how much time I was willing to put into preparing the parts and this was determined by what coatings I was going to use. 

A few months ago I had made the decision, earlier on in the process, to paint the rear differential pumpkin/housing with POR-15. I did this because it would be quite difficult to handle any other way. I needed a strong, stable coating; mechanically stripping the complicated casting would be a big challenge; and I didn't want to disassemble the whole thing to take it to the sandblaster. I did the work and the results were good. 

This however left me with a small dilemma. One of the things I've learnt about POR-15 is that, once it's cured, you cannot easily topcoat it. In their ecosystem, you have to topcoat the paint at just the right time otherwise you'll have to mechanically i.e. with sandpaper rough up the POR-15 coating and then etch prime it.  This is because POR-15 has a ton of solids in it. The paint goes on really well with a brush and then flows out so that you have a nice, streak-free coating. But, once it cures, it ain't coming off, and hardens to a glossy-like finish. Paint won't stick well to cured POR-15. 

After scratching my head for a little bit, I decided that this might turn out to be OK, for reasons I'll explain later. 

The rear axle case I've started on had some paint on it of indeterminate quality so, I decided my best bet was to start mechanically stripping it. My thinking was, since I didn't know how well this stuff was going to stick long-term, I might as well take it down as well as I could. Paint likes bare metal, right? This has, in retrospect, been a bit of a bad idea. I've spent a lot of time with the angle grinder trying to strip off old paint that probably didn't need to come all the way off. Complicating things is the fact that I can only get so far into the nooks and crannies of the axle case with my various wire wheels and flap discs. In retrospect, I probably should have taken a scotchbrite pad to the axle case or some 240 grit sandpaper and then just topcoated it with something to make it look nice. 

Lesson learnt. 

So as you can see as it sits at the time of this writing, the axle is sorta mostly-stripped (and slowly rusting) in a corner of my garage. I will probably finish the mechanical surface prep, then hit the whole axle case with some spray primer (I have bought the POR-15 primer) and then topcoat it. Or maybe I'll trust the "DTM" label on the POR-15 topcoat and just do that instead. 

Backing Plates & Spindles

Some parts are smaller, and consequently we have other options. The next things outboard of the axle case itself are the spindles and the brake backing plates, so it's these parts I turned my attention to next. 

The spindles I have are... rough. Partly my fault: I dimpled the mating surfaces when I foolishly drilled all the way through the distance pieces to get them off. One of my spindles, furthermore, has some scoring and damage on the shaft probably from when a wheel bearing failed in the past. Hopefully however, there isn't any scoring where there are sealing surfaces or bearing surfaces. And I'm hoping I can put some schmoo in underneath the distance pieces so that there won't be any leaks. 

Anyway, I decided with these parts to keep it simple: wire wheel all the corrosion off of the outer collar of the spindles, then prime and paint them. I decided to use the POR-15 etch primer I bought, reckoning that it would work well for this application. Then, I figured I'd try out their top coat product as well. The thinking was, I wanted to use one topcoat for the whole project so that it would look uniform and... well, nice. Since I'd already used POR-15 on the differential housing, it was an easy choice to decide to use their topcoat.

The job turned out... alright:

I mean, I think it turned out okay. You can see the masking job I did was... not great. I have a better idea now how I would mask the inner surface where the flange gasket goes for next time. But you know, overall the coating came out OK. There are some drips down below the paint, which you can't see in the photos, on the surface where the brake backing plates will be. I'm not sure how I'm going to solve that, perhaps I'll have to sand the coating down so the surface is perfectly smooth. In retrospect, I should for sure have masked this area. 

With the brake backing plates, I decided to do something I'd never done before: sandblasting! The brake backing plates themselves are 'complicated' parts in the sense that they're not flat, with lots of curves and angles and nooks and so forth such that using a wire wheel to prep would be frustrating. The parts are conveniently small enough to fit in a blasting cabinet so... what the hell, right? 

I went to Langley U-Blast for this job because my garage is not a great place for sandblasting (no space) and my compressor is, uh, underwhelming. Having never sandblasted before, I can tell you that it is really straightforward. It's not hard to do. U-Blast charges in 5-minute increments. Both parts cost me $40 to process, probably because I'm a novice and wasted time / didn't do it correctly. 

Once I got the parts home, I hit them with the POR-15 etch primer. I wanted to prime the parts quickly to prevent them from flash rusting. Once the primer had cured (which happens really quickly, actually!) I decided to use the POR-15 topcoat on the inner i.e. 'outside' part of the backing plate, leaving the primer in place:

The topcoat, I've found, is a very 'high-solids' paint. They very strictly tell you not to shake the can, and stirring all that stuff is hard on the hands. It's like stirring peanut butter. 

When you brush it on, they also advise you to do really thin coats. This is not always easy and, as you can see above, I ended up with some runs in the finish. Since I am not a professional and no one will ever see these parts underneath the truck, I'm not all that worried about it. 

After coat #1 they suggest you recoat in two hours. Here, I made my second mistake on these parts by re-using the paint that was left in the cup I decanted for coat #1:

Obviously, this paint had (of course!) started to cure and I ended up with some ugly-ass rookie brush strokes in my final finish as I touched up the parts where the paint was thin. You can also see some runs in the finish where the paint pooled as it cured. 

These mistakes aside, I think I'm happy with the finish in the sense that it seems to be tougher 'n hell, and in the parts where I got it right it actually looks pretty good. I don't have any reservations about using this product on the rest of the axle parts.

Next up: I will attach the differential housing to the axle casing, scuff up the POR-15 on the differential housing and finish the prep on the axle housing, then prime the whole lot and paint with the etch prime and POR-15 topcoat method I used with the backing plates. Probably. Maybe I'll just be brave enough to brush on the topcoat.