Spray Painting

Originally Posted by TimberWolf

Might as well state the obvious - Read the fine print on the back of the can for specific info first . . . ;)

Second obvious point: Don't use cheap "bargain" brands of paint; and don't mix different brands - if you're using Krylon Enamel color coat, and you need to use a primer, then make sure it's Krylon primer for enamel paint.

Third obvious point: I don't particularly care if somebody reading this took a few shortcuts, used 20 year old paint, mixed laquer and enamel, did the job in a grain silo, and won the "Best Paint" award at their local LAN party. The fact is: a.) You're lazy, and b.) You lucked out. The following are established guidelines for achieving consistantly good results . . .

Work Area
Generally, for spray painting, you want a clean and well lighted area with low humidity. Temp should be between 65 to 80 F, and the area should be well ventilated. You won't usually get nice results in a damp, unheated basement with a 60 watt desk lamp.

Flourescent lighting is best. For large projects (like a case) create a work area on an old table using a sheet or plastic drop cloth to control overspray by suspending one edge from above to form a "back panel" - this can also help to control drafts. For smaller parts, cut a larger box open to make a "poor man's spray booth" with sides, a back panel, and a floor - line it with a kitchen trash bag so you don't get cardboard fibers and dust on the finished piece.

Preparation
Clean plastic parts in warm, soapy water to remove the molding release compounds that are always used during their manufacturing process; and dry them off with a blow dryer. If you're not painting them immediately, put them in plastic bags until you do, and don't handle them with your bare hands - you'll re-apply skin oils to the parts you just cleaned.

Metal parts (including case panels and frames) also usually have an oil or silicone spray coating to prohibit corrosion (or simply lubricate forming operations). Clean them initially with automotive brake cleaner spray, mineral spirits, or laquer thinner (depending on your tolerance for the resulting fumes), and dry them with a blow dryer or heat gun. Handle the parts as little as possible (especially exterior surfaces), and bag them if you're not painting them promptly.

It's a good idea to go over all the metal surfaces destined for paint with an Extra Fine Scotch-Brite(tm) pad - think of this task as more of a "polishing" rather than a "sanding" operation - and don't do it where you'll be painting because of the dust it will create. Strive for a uniformly scuffed appearance. Rinse with your preferred solvent and dry as before. Note: This is definately a dirty and labor intensive extra step, and it isn't always required after a good de-greasing - but it does help promote good adhesion. If you're blowing some Hi-Temp Satin black inside your no-name case, you could skip it - If you want compliments on your Jade Green Metallic Lian-Li at the next LAN party, then roll up your sleeves . . .

Most finishes applied to bare metal parts require the use of a primer. In that case, I strongly suggest basing your color selection(s) on automotive paints, and using a "self-etching" primer that is compatible with the brand you choose. The main purpose of primer is to provide a surface that the color coat can adhere to; self-etching primer chemically "roughens" the base metal so that a good bond exists there also. A secondary purpose for some primers is to fill in very minor surface imperfections, which may require multiple coats while wet sanding between applying them. Read the labels - There is a type of "non-sandable" primer, and that means exactly what it says: For use on a ready-to-paint surface only.

An exception to the above "primer info" would be Hi-Temp or heat resistant finishes and texture paints (like "wrinkle" finishes). Most of these are meant to be applied to bare metal; but again: Read the can for specific info. Using the Scotch-Brite(tm) pads before applying these types of paint is optional, but it does improve adhesion.

When selecting a primer color, you'll typically have choices ranging from Flat White to Flat Black, including Light and Dark Gray, and even a Dark Red / Brown. While the options may seem confusing, as a general rule you should choose a primer color that will closely match (and not adversely affect) your base color, while providing some visual contrast that allows you to easily judge how you're applying the color coat: If you're shooting a Yellow case, you would want to use a Flat White or Light Gray; for a Green case, a Dark Gray would be fine. Under most circumstances, either Light or Dark Gray will be most useful.

Mask off anything you don't want painted, using card stock, sheets of paper, and / or masking tape. Don't confuse common "crepe tape" with masking tape (which most people do): Masking tape is labeled as such, has a finer grain (making it more flexible), and the adhesive isn't as tacky (making it easier to remove). It's no big deal if your protecting the inside of a door panel from overspray, but if you're executing a multi-color design for a case exterior, it makes a difference.

Application
Shake spray cans for at least a minute after the agitator ball starts to rattle to ensure the paint is well mixed, and regularly shake it as you use it. Warm the can in a pan of hot (not scalding) tap water for a few minutes before and after you initially mix the paint - this raises pressure in the can for a finer spray pattern, and thins the paint for better flow. Put the can back in the hot water whenever you're not using it, and do your shaking (whenever you take it out) away from the parts so you don't fling drops of water on them.

All parts should be at the same temperature as the paint and painting area. Metal parts can be warmed to slightly above room temp with a heat lamp or gun, and this can be especially beneficial for heat-resistant and texture paints to improve blending, flow-out, and to produce a finer "grain". Do not do this if you're using laquer-base products - the laquer solvents will flash off too quickly, and the finish will be dull and rough in appearance.

Paint "hidden" areas, inside corners, or anything other than the "appearance surfaces" first with a light spray coat applied 8" to 12" from the part. Use steady strokes, concentrate on maintaining the distance, and start the spray before the part - ending it after you pass it. You want a light "tack coat", not a solid "color coat"; and you're practicing the technique you'll want later for the readily visible areas. A tack coat will still show some of the base finish, and appear slightly dull, even when wet.

Some places may be tight on space, and you'll have no choice but to just blast a shot of color there - go light. Runs and sags are caused by too much wet paint, too soon. Keep paper towels handy, and if you see runs or sags starting, gently touch a corner of the towel to it to soak up some excess; then (if possible) turn the part so the area with the build-up is horozontal.

I've painted enough cars and 'cycles that I'm comfortable working with large panels vertically. If you're unsure of yourself, and you have enough work area to do so without excessive handling, then lay them flat to minimize the chances for runs / sags.

After you do all edges, sides, channels, and such you can apply a tack coat to the appearance surfaces. Then STOP, and let it all sit for 10 to 15 minutes. This tack coat is what's going to provide the bond to the parts, and minimize the need for excessive paint for the finish coat. Put the can back in the hot water, and you should have been shaking it after every few passes or so. If the water's cold, go get some more - it'll help kill the time, but don't get lost - if that tack coat dries, you'll have a lousy finish.

If at any time you're in doubt about "how much is too much" paint - go light. You can always shoot a second tack coat; but you can't go back if you spray too heavy. I prefer to do all those edges and "hidden" areas so that the overspray from my final coat finishes them off too. The final coat is applied using the same technique as above, except you maintain the distance, and make slightly slower passes - the most common error is to get too close, which puts a lot of paint in a very small area very quickly. The paint should appear evenly wet and glossy, but not thick.

You're done. If practical, cover the parts so dust can't settle on them, resist the temptation to apply "just one more coat" or handle them, and leave the area. Depending on the paint, give the parts 24 to 48 hours to dry thoroughly before handling them. After that time you can inspect your job. If you find you "missed a spot" (and we all do), don't panic - with a little thought you can usually come up with a "creative masking" solution without resorting to a re-shoot.

Vinyl Paints
These are generally automotive finishes for use on upholstry and other plastic interior parts. Locate them at most auto supply stores - Color choices are somewhat limited, so inquire about any other colors they may not currently have in stock. I swear by them for repainting drive bezels. They usually provide a Satin finish - midway between a Gloss and a Flat finish; and they dry quickly, with no special parts prep required.

Metallic and "Anodized" Paint
These finishes usually require at least a two-step process - Initial application of a metallic-colored base coat (Silver, Gold, Aluminum, Copper, etc.); and then a translucent color coat is applied. The choice of base coat alters the appearance of the final result. The application of the base coat also affects the final result - skip the proper prep work, and you'll ruin the job - so don't take any shortcuts. Be certain that all products used are the same brand - NO SUBSTITUTES. Because the translucent color coat is usually very thin, a clear gloss final finish is recommended. The base coat may or may not require a primer - Read The Can! and follow all the prep info provided here. Build up your skills with a few projects first, and make these guidelines habits before you consider using these types of paints. They require a lot of work and patience, but the results are worth it.