Congratulations to you if you've handled all of the bodywork and prep on your classic truck project and now you feel you are ready to lay down a custom paintjob. We don't have any retroactive awards at CCT to present to you for learning the ins and outs of dealing with substrate materials designed for use by trained professionals, or reaching the status where your truck is ready for color - it's just one of those personal victories.
Unfortunately we do have to warn you that everything you have done to get your truck ready for a shiny topcoat can be destroyed if you proceed from this point to the final stages of painting without a working knowledge of how to handle topcoat problems that might arise. Unlike mechanical procedures such as building an engine where a misstep can be corrected merely by unbolting a mistake and then moving forward within minutes, paint is an entirely different animal. One wrong move here and it's back to step one. A worst-case scenario is when things go terribly amiss in the paint booth and the only remedy is to strip the aborted paintjob down to the bare primer and start all over again. Stripping it back down to the primer probably doesn't sound like a big deal until one has discovered the probability of leaving the primed surface intact isn't likely. If the botched paintjob has been allowed to dry get ready to buy more sandpaper and revisit the bodywork experience. This is where an experienced painter (someone who has already screwed-up) will know it's time to grab the thinner cans "muy pronto," and start washing the problematic paintjob onto the spray booth floor. For the guys who are shooting one of the new waterborne products it's not quite as traumatic because a garden hose can be used to literally hose-off the botched paintjob with tap water.
OK, now that we've warned you about major custom paint nightmares we are going to explain how to get ready to paint, and then how to identify and eradicate paint flaws.
Step one is to understand painting is an art that's perfected by practice-kind of tough when as a hobbyist you paint maybe one truck a year, so here's a list of things to do right (as in correct) before you pull your spray gun's trigger.
Proper preparation is vital and as you'll see plays an important part in causing or preventing many of the following flaws illustrated in the captioned examples. In a nutshell, any surface to be painted should be properly cleaned before painting. The generic term for what you are looking for is a silicone stripper, or pre-cleaner. A few of the brand names that market such a product are RM Pre-Kleano, House of Kolor KCA100 aerosol surface cleaner, or PPG One-Choice waterborne pre-cleaner. If the surface is bare metal and the paint manufacturer's instructions specify it, the surface should be chemically treated as well. Before beginning to spray, use compressed air from a source known to be free of moisture and oil (drain your air compressor and check for the presence of oil and excessive water). Once you have established your air supply is contaminant free use an air blower along with a tack rag to remove all dust and dirt (Don't press the tack rag down too hard, or it will leave a residue that causes paint imperfections similar to massive fisheye).
Today's modern paints include both solvent-based and waterborne types, and most require the addition of solvents (known as thinners or reducers) to produce the proper spraying viscosity. Others may simply require the addition of a second component at a prescribed ratio to obtain a sprayable consistency. The majority also have hardeners or catalysts, which must be added to ensure correct color match, gloss, hardness, drying time, or other characteristics necessary to produce a top-quality custom paintjob. It might be a good idea to take the time to review the instructions and any specific finish material data sheets that are available.
Most of the paint companies will tell you that it's never a good idea to mix materials from various manufacturers. Beyond the obvious fact they want to sell you as many products as possible, there are a few good reasons not to do it. The practice of mixing different paint brands together is known as cocktailing and it opens the door to hideous incompatibility problems like you won't believe. If you do mix different brands together and then run into a problem there isn't a paint store or manufacturer in the world that will warranty your concoction. That said, professional custom painters have been cocktailing paint since the earliest days of custom paint. That's how it all got started. The moral of this story is if you want to experiment it's your baby, and if you need to play it safe then find a good brand. In future editions of CCT we're going to load up our spray guns and take a shot at finding out who the good brands are, and what they have to offer, so stick around, it's going to be a lot of fun.