Checking
Checking, sometimes referred to as crows feet, are cracks of various lengths and widths that show up in a topcoat (if you’ve ever been to El Mirage or any other dry lakebed you’ll recognize checking right off the bat). This is one problem that has a number of possible causes. The most common causes are excessive film thickness, too short of a flash time between coats, force drying your undercoat (like using the blowgun to dry primer), and sometimes by using too much hardener or catalyst in the primer or paint. The only way to fix checking is to strip all crazed and cracked paint film and do the whole job over. You can usually save yourself a whole lotta work by preventing the problem by actually reading and following all label instructions, by removing checked surfaces completely before you spray over ’em in the first place, and by making sure your material, both undercoats and topcoats, are thoroughly mixed before spraying.

Dust ‘N Dirt
Crap in your paint is by far the most common of all paint headaches, and actually for those of us (read that most of us) that don’t have access to a big-buck spray booth, one that we’ll never completely rectify. That said—all we can do is work to reduce the amount of dust and dirt as best we can. This can be accomplished by making sure that your spray environment (garage in most cases) is as clean as possible. Wet down the floor before you spray, and if possible between coats. Make sure the vehicle’s surface is clean (I’m talking about all around the windows, door, hood, and cargo bed too). Don’t forget to tack off your masking paper and tape masked areas as well. And you should use a fresh new tack rag as often as possible. Another thing a lot of people don’t think about is static electricity—it really does come into play in this situation by actually attracting dust to the vehicle like a magnet (especially after all the compressed air blowing and hand wiping done during your final prep). Running a ground strap from the chassis of your vehicle to a good ground in the garage will help out more than you could imagine. I’ve tried it, continue to do it, and think it really does help. Personally I’ve given up hope for a completely dust free paint job in my home two-car garage—I’ve sometimes been able to bury very minor dust spots using another coat of color, but in most major dust cases the surface will have to be sanded with 1200-grit or finer paper and either buffed or resprayed. Unfortunately a clean professional booth is the only real solution to this one.

Edge Mapping
Edge mapping, also known as feather edge lifting or edge ringing, is caused by the solvent from a fresh topcoat penetrating a sensitive area of an undercoat (most commonly the featheredges of a repaired area). You’ll recognize it as a wrinkled area outlining a repaired area. When painting a vehicle with repair areas (meaning almost everything those of us who can’t afford a new steel aftermarket body will end up painting), it’s always a good idea to use a two-component primer surfacer, water-base primer surfacer, or an appropriate sealer that’ll create a barrier between the repair and the fresh topcoat. If you do encounter edge mapping you’ll have to sand smooth or remove the affected area and seal it with a good barrier coat of some kind (your paint supplier will be able to recommend one for ya). Another thing that helps to prevent featheredge lifting is to always final sand a repair area with 400-grit of finer paper—the finer the final sanding, the shallower the sand scratches will be and there’ll be less area for the solvent to attack.