Bare steel paint prep

The HF sprayer works pretty well once you dial it in.

I used it to paint a car. Came out great.


Seeing this project is making me a little jelly of your prep.....

 

So what process do you plan to use for the yearly touchups on scars?

 

Clean it well with rubbing alcohol, let it dry, rattle can it, call it good.

 

I have a pair of cali sliders bare steel sitting in a garage since Dec 2023
I plan on just tying some wire and lifting them up with a forklift and using self etching primer and then bunch of coats of rust-oleum

 

eastwood offers some 2k rattle can products as well... for smaller projects, it's much more worthwhile than breaking out the compressor, hose, gun, and cleaning supplies.

 

Yes, I looked carefully at Eastmans and some other higher-end paints in cans, just couldn't find any with verifiable high long-term rust resistance. Was really impressed with the salt-water torture testing done in the long video I linked to earlier.

 

Might work out fine. If you have a place you can safely spray 31% hydrochloric (aka muriatic) acid, and an acid-rated sprayer to use, it works wonders. Fast, low-effort, nearly complete clean. (Not quite as good as electrochemical methods or media blasting.)

Best in warm or hot weather. I bet it's much slower in temps below ~50ºF.

 

yeah, i had watched that video a few months ago. i can't stand the presenter, but i also can't argue with his testing methods or results.

 

The magic of Amazon Prime delivered me a cheap HVLP sprayer (about $60ish.) Never used one before so I put half a quart of rubbing alcohol in it to figure out spray patterns vs. air flow, and what my little 2 gallon 1HP air compressor is capable of. (Rubbing alcohol, not water, because alcohol evaporates quickly & completely; didn't want even the tiniest trace of moisture in the HVLP gun which could cause local gunking/thickening of the metal primer I'm using, which cures not by air-drying/evaporation, but through polymerization promoted by water vapor/humidity.)


HVLP sprayer is definitely the correct tool for this job. The essentially 100% stainless/metal seals & channels inside the simple HVLP mechanism can be thoroughly cleaned with acetone pretty easily. R.I.P my poor $400 airless sprayer from 2 days ago.


Some equipment, along with the obligatory pile of dirty crap that painting usually seems to require:







Here's the final-final after 2 to 2.5 coats of primer. Basically this primer is about 30% aluminum powder (Al) by volume in (I believe?) a urethane-type substrate, probably with some other magic ingredients to help the aluminum powder bond & flow well onto steel. The Al is lower in the galvanic corrosion hierarchy than steel, so it will corrode first & preferentially, sacrificing itself (for a time) to protect the steel.








I had some issues with the 40-micron filter basket in the HVLP sprayer not allowing adequate flow, so I thinned the primer a bunch -- too much -- and it still didn't spray hardly at all. Ended up removing the 40-micron filter entirely, but I had already over-thinned & couldnt go back. Resulting finish is probably not as smooth as it could be, i.e. when the excess thinner evaporates it leaves (microscopically-speaking) too-large gaps between the solids in the coating, resulting in a rough surface. But this was a second coat anyway so I didn't sweat it too much.

Made sure to coat every square millimeter of surface, using a foam brush to get into the weld joints that are inaccessible to spray:




Also completely flood-coated to full depth the inside of the single open tube in these sliders (no other openings) then let the excess drip out vertically into a catch container:



Letting it all cure overnight & plan to do the first coat (of 2) of the 2-part epoxy black matte finish coat tomorrow.

Learned a lot on this project. I've done plenty of 1-step rattle-canning on steel in the past. This is my first time ever prepping bare steel down to base using acid, using metal-specific primer & an epoxy finish coat, using an HVLP sprayer, etc.

Without a proper spray booth & wire-suspension system this job is taking excessive time, i.e. have to spray, wait 6 hours, flip the parts over on their resting stands, then spray again, for basically twice the work per coat in a 2-coat primer / 2-finish coat process. I have a lot more respect for what a proper paint shop can accomplish with their dedicated painting spaces & equipment. I don't think I've saved any money over just sending this to a paint shop for maybe a $400 fee or so, but I value the learning and also the certainty that I've covered 100% of the surfaces.

 

Alright, it's finished. Rather than add to this thread here, I re-organized the whole process into a more coherent write-up over at this new thread. A couple photos of the finished parts are at the bottom of that post.

TL;DR it appears to have come out pretty good. Certainly good enough considering my skills & doing the work in an open back yard w/ dust, bugs etc. occasionally filtering down out of the trees.

https://www.tacomaworld.com/threads/one-way-to-paint-a-steel-bumper-diy-notes-pics.836279/