It's pretty exciting to see do-it-yourselfers attempting some of the more difficult aspects of street rod building on their own these days, and bodywork and painting are prime examples. These tasks, which in the past have more often than not been relegated to experts, are ones more and more are tackling with surprisingly good results. But as with any craft, painting is an art that's perfected by practice-kind of tough when as a hobbyist you paint maybe one vehicle a year. So it's with this in mind that we decided to try and put together a bit of a primer (no pun intended) referencing some of the most common paint problems many of us have or will encounter during the course of any paint job or jobs we've done or will possibly do. Hopefully the following information will help us novice painters identify-and with any luck rectify-some situations that'd otherwise have us tearing our hair out or tossing our spray guns in the trash bin.
Prepping For Paint
In a future issue we'll revisit body work and paint prep in a much more in-depth manner, but let's touch base on the obvious for the time being. As is the case with many aspects of hot rod building, proper preparation is key, and plays an important part in causing or preventing many of the following examples. In a nutshell, any surface to be finished should be well-cleaned before painting. If the surface is bare metal and the paint manufacturer's instructions call for it, the surface should be chemically treated, as well. Use compressed air and tack rag to remove all dust and dirt-remember, no amount of primer or paint will cover up a badly prepared surface.
Today's finishes are extremely complex and include both solvent-based and waterborne types, and most require the addition of solvents (thinners or reducers) to form 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 other catalysts, which must be added to ensure correct color match, gloss, hardness, drying time, or other characteristics necessary to produce a nice, successful finish. And please, always make sure you take the time to read the instructions and/or any specific finish material data sheets accompanying whatever paint and material you choose to use! And again remember that it's never a good idea to mix materials from various manufacturers.
Once you've got your surface prepped and ready to be sprayed, the next step would be to know the type and color of paint your project requires-with this determined, follow the manufacturer's instruction for preparing it exactly. If you have any doubts about how to proceed, don't guess! Contact your paint supplier for help, because improperly prepared primers, sealers, or paints will rarely produce a good finish and often cause huge amounts of heartache-believe me, I know from firsthand experience!
A major attribute which determines the sprayablility of paint and how much film may be applied is its viscosity, or consistency. Following the instructions on the cans will get you close, but for professional results you gotta use a viscosity cup. Unlike the old days, when I used to just watch how the paint ran off my paint paddle, the advanced finishes of today need to be handled much more professionally. It only takes a minute, and checking paint's viscosity is a simple but very accurate way to measure its thickness. Viscosity cups are available anywhere automotive paint is sold, and they're easy to use, too.
Always mix your paint in a clean, dust-free environment. Paint's got a remarkable ability to attract dirt, and dirty paint will not only possibly muck up your spray gun, but it will also ruin an otherwise good paint job. That said, make it a habit of always pouring paint into the cup or tank (if you're using a pressure pot) through a paint strainer.
Okay, now that we've touched on the common sense basics, let's move on to our primary focus-recognizing and addressing the causes of the most common of paint problems. Just keep mind that I'm just a hobbyist, not a trained paint pro, and this is just info gleaned from asking questions and personal experiences-meaning if you read this and then have a problem of your own, I won't be coming over to fix it for ya.
Fisheyes
Fisheyes are small, circular, crater-like openings that appear either during or shortly after you lay down a coat of paint or primer (though primer is often much more forgiving). They're caused primarily by spraying over a surface that's contaminated with oil, grease, silicone, or wax (Note: the mold-release agent on a new fiberglass body is a really common culprit), but can also be caused by using thinner or reducer in place of a wax and grease remover during your pre-paint preparation. Though not as common, an occasional cause may also be painting over an existing finish where an additive like Smoothie (a fisheye preventer) had been used.
Wrinkling
Wrinkling, often called lifting, is when an existing paint layer shrivels during the application of a new finish or as the new finish dries. This is caused by the solvents in the new finish attacking the old finish. You'll most likely see this malady when recoating enamels or urethanes that are not fully cured, or if and when you exceed the maximum flash (dry) or recoat time during application. It'll also sometimes happen when you recoat a basecoat/clearcoat finish where the old clearcoat had an insufficient film build. In this situation, you'll have to strip and refinish. This circumstance can be prevented by not exceeding a product's maximum recoat time during or after application, by not shooting lacquer over enamel or urethane, or avoiding spraying under or top coats excessively wet.
Bleeding
In this particular case, bleeding isn't something you'd grab a bandage for-bleeding in this situation is when you end up with a discoloration in your topcoat color (most commonly a red or yellow stain) when painting over an existing finish. This is because the solvent in the fresh topcoat sometimes dissolves soluble pigments in the old finish, allowing them to seep upward into the fresh paint, thus discoloring it. You'll also sometimes see this when red crme hardener used in body filler bleeds up through a light color. You can sometimes repair a situation like this by letting the stained topcoat fully cure and then spraying a two-component sealer over it followed by a fresh coat of color. If you think you may encounter a possible bleeding situation, your best bet would be to use a good sealer before topcoat, or in the case of body filler under a light topcoat using white crme hardener instead of red or blue.
Die Back
Die back, also known as dulling or hazing, is the dulling of a finish's gloss or shine as it dries or ages. This one is pretty common and has quite a few different causes. I've found that you'll be more susceptible to die back if you don't allow adequate drying or curing time of your undercoat, or if you close up a freshly painted vehicle in a booth or garage with no air circulation. The latter cause happens because in a sealed environment the evaporating solvents from the new finish hang around in the air and react with the still-drying paint surface, causing it to dull out. Other possible causes are too short a flash time between coats, using cheap off-brand thinners or reducers, and sometimes an excessively heavy and wet final coat. You can repair die back by letting the finish dry thoroughly and then cutting and buffing it or you can sand and refinish. You can also help to avoid the problem in the first place by applying your topcoats according to the product's directions, allowing sufficient flash times between coats, using the correct and/or recommended thinners or reducers, and making sure you've got good air flow around the vehicle as soon as it's tack-free.
Checking
Checking, sometimes referred to as crow's 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.
Sags
Also sometimes known as runs, hangers, or curtains. Sags are, along with dust, one of the most prolific paint problems for the hobbyist or occasional painter. I have to admit, in my many quests for slick finishes I've created way more than my share of curtains in my day. The most common causes are holding the gun too close to the surface, moving too slowly across a panel, and double coating an area. Over-thinning/reducing is also a possible cause, along with trying to paint in an environment that is too cold (I've done that one too). To fight runs and sags, you've gotta hold your gun perpendicular to the surface and keep it a steady and correct distance from the panel, all the while moving it fast enough that you don't pile the paint on, yet slow enough to get good coverage and flow-a process that comes with practice and experience.
If you do "sew some curtains," in some cases you can wipe the area with a solvent-wetted rag and then clean and re-spray the area (seldom a first choice), or you can keep on going and wait till the paint fully cures and then sand and buff or sand and re-spray.