Auto undercarriage components What SPI product(s) to use?

SPIuser

New Member
Hello:
I am restoring rear suspension components for BMW e30, namely the rear sub-frame and both lower control arms.
I'm not new to the resto hobby, being more of a hobbyist mechanic to-date; now spreading my abilities into bodywork and finishing; so in short, new to coatings.
I chose to have these items de-rusted via chemical immersion by a professional service. This same service then outsources the parts to an immersion e-coater. I believe the process includes an oven bake just as entire car bodies/frames are done. As to what specific brand coating the outsourced e-coater uses is not known to me, nor have I asked. In past exercises, I have opted for hired out powder coaters for undercarriage components, with good success; I wanted to try this methodology this time.
The parts I received back are coated inside and out; some visible surfaces are smooth and look great, other areas feel rough and basically look surface pitted. My objective is to select a finishing process whereby I can achieve a greater degree of smoothness across most all these visible surfaces for appearance sake. I don't believe I should get into hard sanding the e-coat and potentially exposing bare metal. An option I did not exercise this time from the de-rusting service was to take the parts back after chemical immersion to work the raw metal before returning said parts to their immersion e-coater.
After much reading and research, I remain somewhat in doubt yet of what SPI coatings I want to use to achieve the next step(s); and I seek input from people wiser than I. But I do believe I think I should head for SPI Hi Build primer next and sand. After that, I am really up in the air what to do.
I have a semi-sophisticated homemade spray room in my garage, a 1 1/2 hp Rol-Air wheeled electric compressor, and plan on using CA Tech cup gun. Admittedly, I do wonder if I should consider HVLP.
But first thing is first, SPI HiBuild Primer next?
Thanks
Chris
 
Really depends on what you are trying to do. What is your desired finish? I will say that In the future, if you have more to do, he best way to do parts such as yours is to media blast then 2-3 coats of SPI Epoxy. Far superior to any aftermarket ecoat. Test your ecoat BTW, use some quality reducer or good lacquer thinner, (most is garbage these days) and rub on a spot. If it softens or the color comes off on the cloth it is garbage and should come off for best results and long term durability.
Urethane primers such as Hi build are for surfacing, Meaning leveling and filling. They are not designed for bare metal. Epoxy is what you should always use as your base, due to it's incredible adhesion, durability, flexibility and corrosion resistance. Some of us use epoxy for build as well.
 
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Thanks for replying @Chris_Hamilton! Desired finish = basic black, nothing particularly fancy, probably a matte or satin black finish.
I considered media blasting, and will likely pursue that for all the trinket pieces, brackets, hardware in this manner. I chose immersion de-rust and immersion e-coat largely on the basis that these three major pieces of the rear suspension I desired to have coated internally and externally. Be as it may, probably not the best rationale; but like I stated, I am ranking this up for experience and building skill sets.
I will check this e-coat finish with lacquer thinner, as you recommended, I do have a 3 gallon can of Sherwin Williams branded lacquer thinner. I would hope it meets or exceeds the standard you set forth. I will report back shortly with my findings.
As to urethane primer, high build, I concur, for leveling and filling. I'm gathering from your comments that urethane is different than epoxy. I understand epoxy could be used as a build. I am open to taking the next steps with either product.
Thank you for the advice!
 
In a nutshell, epoxy is the best option for bare metal. Many of us will epoxy then use a filler primer to level. A urethane or poly primer. Urethane is not a good choice for bare metal due to it being somewhat porous and adhesion is not great.
Epoxy would be a great choice for suspension components. If your Ecoat is good, and you are just wanting a nice uniform finish, then scuffing and shooting it with black epoxy would give you a nice durable semi gloss finish. 2K urethane would require sanding, then topcoating.and unless you are trying to get your parts super slick looking would not really be necessary. Urethane is also more prone to chipping. Epoxy is flexible and tough.
 
I did the lacquer thinner test on the e-coat as was suggested. No softening or smudging or any rub-off on the cloth.
 
I think the guidance for epoxy undercarriage went from 2 coats to 3 coats a while back. This makes sense because it's hard to get perfect coverage on every coat. Doing 3 coats gives better assurance that the thinnest areas have enough film thickness.
 
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