Tips... A long post
Use a good paint, hard to go wrong with Rustoleum aerosols in their industrial enamels.. Painting involves prep the metal , clean the metal, prime the metal, finish coat the metal.
Remember that the condition of the metal surface being painted will become transparent, meaning if its pitted, bumpy, has paint build up from previous jobs, that all flaws will show through the new paint. The new paint just lays on the metal surface, it will fill in and level somewhat, but will not "fix" bad metal surfaces...
The metal parts that are deep pitted have to be sanded flat by started out with aggressive paper like #80 grit- 100 grit for fast cutting then, progress upwards to a #240 -320 /400 grit so sanding scratches will not show through the paint. ...
If it has decent factory paint on it and minimum rust, you may get by with just some #240 scratch and finish up with #320/400. Get the metal surface to look smooth and flat, remembering that pits and low spots will show so they should be sanded on the edges to get "feathered in" to the surrounding paint coat thickness. The finish sanding with the #320/400 paper will give the metal or existing good paint, a microscopic scratch or, " mechanical tooth" for the paint to bond to...
When the metal is smooth to the hand and looks flat in the light, your paint will look flat. Shine a light down the metal at different angles and you will be able to see how it will look when finish paint coated, sans the shine of course...
When you have the metal /old paint coat the way you want it to look good, whether it was a rough rusty cut or just a factory paint scuffing, just clean it with a clean microfiber cloth with lacquer thinner and let it dry. ... Use nitrile gloves when handling painting chemicals...
Go ahead and shake your Rustoleum's metal primer paint can (match the primer color with the final coat used, use red primer with red and darker tints, use gray primer with whitish/gray finish coats, this allows the finish to cover easier) Shake, shake, shake, the paint can until the agitator ball inside of it rolls around easily. In between spray passes, shake and shake. These new spray heads on Rusty's paints need a lot of agitation as to not clog up ...
Use a good respirator mask, rated for paint spraying. The paint spray once airborne and inhaled, kills brain cells, and stays in the lungs. I know, been there done that, my brain cells are quite diminished after 40 years of spraying paints and chemicals. ...
Stop, dont spray your project at this time... You need to practice spraying, but not on your project...
Pick up a old piece of metal somewhere and practice on it. Too much work getting your project sanded and prepped, in trying to learn on it and make mistakes that has to be fixed....
On your practice piece and later your project when your confiident, shine a light at an angle either from overhead or from the side, on the metal before you start spraying, good lighting matters. What paint you see hit the metal, is what you get.. Hold the cans sprayhead about 8 inches from the metal and off of one end. Push the button and have the paint spraying as you get on to the metal....
Try to keep the same speed in movement as you spray a pass across the metal. DO NOT start the spray or STOP the spray when the spray is hitting the metal. Start the spray a bit off of the metal and release the button just AFTER you pass off of the metal. This prevents paint buildup runs that happens when one stops/starts the spray on the metal....
As you spray across the metal you will see the can's sprayhead is laying out a "fan spray pattern". Keep a mental note of the size of this pattern and remember to "overlap" each spray pass about a inch or better. These overlaps fills in the thin edges the spray has on its very outside edges and will "even" up the coats to keep the overall paint coats "flat"...
The lighting. This is important. Watch at a slight angle behind the can as the spray pattern hits the metal. As you are moving the can across, you will see the paint hit the metal and it will show up as a matte, semi gloss, or gloss finish. For the first coat or two a matte finish is o.k. You don't want the first coat slick as it means it may be too heavy and will sag, it is just your "base" or adhesion coat. .
The second spray coat can be a bit slower pass and let the paint get thicker and shinier. The third and final coat can be even slower as you make a pass and the shine of what you see as the paint hits, is what it will look like when it dries.... For Rusty Enamels its about 5 minutes between coats
The speed of movement of your spray pass, determines how shiny it will be and in keeping out "dry" spots. The trick is watching the finish of the paint, the duller it is the thinner the coat is , the shinier it is, the thicker it is. The thicker laying down of spray is tricky on the last coat, too thin and its dry spotty, too thick and it sags. It takes practice and practice..
So to sum up, lay on the primer with one to two coats max using the same overlap and watch the paint hit the metal and how it lays. If it sags, no big deal, it can be sanded with the 400 and touched up again with primer.. You really don't want to sand on your finish coats as the sand marks will show through most of the time. If you use 1000-1500 grit maybe not though. .
I shoot the finish coats within 20 minutes of laying on the primer. The Rusty enamels dry so fast, that I think the finish paints bonds do well if it gets shot on the primer before it cures too much, say within a hour. ..
Two to three finish coats on top of one to two primer coats should give you the finish you want whether you use matte,satin, or gloss finish.
Practice on that piece of scrap, once you get the hang of watching the paint hit the metal, and keep that can moving at the same slow or faster speed and drop down and shoot the next pass with overlap, it won't be long before you want to paint a larger object. ..
Just remember that aerosols dry fast, and are hard to shoot on something as large as a car hood and not get "mottling or tiger stripes" in it. It has its purpose and can be damn good looking paint work when used with the correct techniques and proper temperatures and with good metal prep. Good luck to you on your project ! Greg
