Bay Area Miata Drivers
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by nick
Looking ahead and looking back on the Miata, sports cars, clubs, and BAMD. Plus of course updates on my Miata.
Entry # 19 (3,970 Views) Posted on August 10, 2011
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On Painting
At our last tech day we painted Zoe's front bumper, which had been roughed up pretty badly by a tree that jumped out into the middle of the road. The tech day was a lot of fun and great chance for everyone to see what's involved with painting a car. Someone asked me during the event if I had enough thoughts on the subject of painting to post a blog about it. As it happens, I do.  
A lot of us with 10-20 year old Miatas have reached the point where keeping the car looking shiny is a constant battle. We wash it regularly, we try to keep a thin layer of wax on it, and we might even clay bar the thing once in a while. Or maybe we gave up on all that a long time ago. No matter how well the paint was treated, garaged, protected, and maintained, factory paint eventually loses its luster. Even Mazda factory paint. It's just a question of time and oxygen content in the air. 
You never quite know what to do about it. You never reach a point where you say, "Well that's it, the paint's done. Time to replace it." It's not like a radiator. Instead you just get more and more depressed each time you wash it. Pulling the trigger on a multi-thousand dollar paint job, or even a multi-hundred dollar paint job is never easy. If you're lucky -- and I mean that in a good way -- the decision will be taken out of your hands by a mad minivan driver late one night on a lonely road somewhere between Twin Falls, Idaho and Winnemucca, Nevada. 
But let's say that one day you wake up and see the light, and then you realize that light is the reflected sunlight from the gleaming finish of the neighbor's brand new Nissan GT-R. And you realize you can no longer in good conscience park your faded sports car on the same block with such automotive excellence. Of course, you say, the GT-R is not a terribly handsome vehicle, especially compared to your Miata, and you'd be right about that. But 193 mph makes up for a lot of awkward sheet metal. And the car is shiny. So you start to figure out your options. 
A couple of things you probably already know about paint, but need to remind yourself. Automotive paints these days are all pretty good quality. Your local body shop likely doesn't advertize what brand of paint they use, although they might say they use the finest available. All body shops use the finest available. Or close enough. The paint you buy at Maaco is not that bad. So don't feel guilty for not taking your Miata to the shop where all the Ferraris are parked. 
Second thing you need to know about paint. It hides nothing, except maybe the color of the primer underneath. If you have a scratch or a chip or a crease or some other blemish on the car, painting over it will just make the blemish glossy. What's even worse, dull paint sometimes hides minor imperfections that shiny new paint is only too happy to highlight. So this is where we offer that sage old advice that a good paint job is all in the prep work. And it's that prep work that makes the difference between a $12,000 paint job and a $250 Maaco special. That and the fact that cars getting the $12,000 paint job all cost way more than your Miata. 
But wait, you say again (such an interactive blog), there's no skill involved in prep work. You've sanded stuff before and it wasn't that hard. If you did all the prep yourself and just took the car to Maaco, you could basically save $11,750 on a $12,000 paint job. That's a no-brainer. And for all intents and purposes, you'd be right. But prep work is a lot more than sanding, and there are a few skills involved. Of course it's nothing you couldn't learn from experience, and prepping a whole car gives you a ton of experience. Way, way, lots of experience. More experience than you can shake a stick at. Way more experience than... okay, you probably get the idea. A car, even a small car like the Miata, has a lot of surface area, and sandpaper comes in these little sheets. You've probably seen them. They have numbers on the back. 
Sanding is all about using progressively finer grits of sandpaper. Those numbers on the back? That's the size of the little grains of sand in fractions of an inch. Sandpaper with 100 on the back has grains of sand that are 1/100th of an inch across. 400-grit sandpaper has grains of sand that are 1/400th of an inch across. I'll leave it to you to calculate the size of the rest of the grains of sand. Actually, calling it sand may be slightly inaccurate. It's usually really hard stuff like carborundum that breaks into little bits leaving really sharp edges. If you need to know more, Google it. While you're at it, see if you can find out whether they use different grits of sandpaper in Europe because they're on the metric system. It's not important, I'm just curious. 
A grain of sand (whatever) that's 1/100th of an inch across will leave a scratch in your paint that's 1/100th of an inch across. A scratch like that will be nasty. Paint definitely won't hide it. This has been proven time and again by lazy people. So after we finish sanding with 100-grit sandpaper, we'll sand the same areas with 160-grit sand paper. This will grind away the big scratches, leaving littler scratches. To get rid of the littler scratches, we'll sand the whole thing again with 240-grit sandpaper (or thereabouts). Since 1/240th inch scratches are still too big to hide with paint, we'll sand again with 400. This is not a job for the weak-willed. That $11,750 savings isn't looking like such a hot deal anymore. 
Two things to know about automotive paint when it's sanded. It's not as dusty as, say, wood. It's actually sort of clay-like. Because of that, it can quickly fill in the little spaces between the grains of sand (or whatever) on the sandpaper, gumming up the works. This is called loading, and it quickly turns the sandpaper into a useless piece of cardboard. To avoid this, sandpaper makers have invented something called non-loading sandpaper. How it works is a mystery (to me, at least), but we want to look for it any time we buy anything coarser than 200 grit. For the finer grits, we can avoid loading by using wet sandpaper, which as the name implies is sandpaper that's designed to work underwater. 
With the bigger grits of sandpaper, we actually have the ability to shape the surface a little. This can be both good and bad. If the surface is not perfectly flat, for instance because it's packed with Bondo, we can wrap our sandpaper around a block of wood and flatten it out. This is where shaping is good. If the surface is already nice and flat and we don't use a block of wood, we could end up putting little hand-sized ridges in the surface, too shallow to notice until the nice shiny paint dries. This is where shaping is bad. Does it sound like using a block of wood is good on both flat and not flat surfaces? Good answer. 
Other areas we don't want to inadvertently "shape" are edges like on doors and trunk lids. I wouldn't use heavy grit sandpaper on these areas at all, but sometimes you have a heavily chipped door edge that has to be cleaned up. In that case you want to sand perpendicular to the edge, with the block, until all the chips are gone. This may leave sharp corners, and you might want to round them off a little, but don't do it. Wait until you're using a lighter grit. They'll smooth out easily, even with 400-grit sandpaper. What you want to avoid is that "soft" look you sometime see on badly repainted cars, where an inch from the edge the sheet metal starts to look slightly curved. 
Try to do most of the shaping with the heaviest grit. When you get down to the lighter grits, consider yourself done with all the shaping. From here on all you're concerned with is smoothing the surface, getting rid of the scratches from the heavier grits. Use a block when you can, and avoid sanding an area any more than you have to. If it looks like you still need to do some shaping, for instance you realize that Bondo patch isn't as flat as you thought it was, don't try to shape it with 400-grit wet sandpaper. Go back to the heavier grit and work your way back down to the 400. 
Besides sanding the car down, prep work involves masking off areas you don't want painted, like the seats and the tires. Windshields, also, so they're easier to see through. Masking is something of a skill, but we can avoid a lot of masking by simply removing those parts that we don't want painted. We'll actually get better results doing that. A carefully masked part will look pretty darn good after the car is painted. A part removed from the car entirely will look perfect, or at least as good as it looked beforehand, which is still better than pretty darn good. 
This is the sort of prep work that most body shops are unwilling to do. For them, masking is usually much faster than removing a part, and if you do it every day and you think you're pretty good at it, that's what you'll do. If we assume we're not that good at it, we're probably going in the right direction. So we'll take the time to remove the part. And we'll make sure to save all the nuts and bolts and the little plastic thingies, and we'll either remember how it all goes back together or be forced to reveal our ignorance on the BAMD forum. 
We'll want to remove as much as we can from the car, while still leaving the car drivable, if not 100% "legal". I put that in quotes because I like to think the issue is something over which reasonable men (and women) might disagree, and not something etched in stone. Do you really need turn signals? Door handles? Brake lights? In any case it's good if your nearest Maaco isn't 50 miles down the Interstate. Alternately we could rent a trailer to haul the car to the paint shop, but that'll of course eat into the $11,750 we've got stuffed in our pocket. 
With any remaining masking, we have the choice of letting a professional do it quickly, or doing it ourselves with a little more TLC. Personally, I think TLC wins. I prefer to mask badges rather than remove them because I have no confidence in my ability to re-install them as Mazda intended. But you may feel differently. On other areas where a little rubber gasket is used between the masked part and the body, I try to have the edge of the masking tape end up somewhere around the middle of that gasket. Honestly, though, we're talking here about a gasket that's maybe 1/32" thick, so good luck with that. Just do the best you can. 
At the last minute, after you've already lined up a buddy to follow you to the paint shop so no one notices you don't have a license plate or brake lights, you may have an epiphany. Or you may not. But you might, and that epiphany might tell you to hold on, wait just a minute, stop the presses. After all that sanding and all that prep and all that masking, why would you want to leave the final step, the most important step, the transformational step, to some unknown muscle-car freak with full-body tattoos and a paint gun? You wouldn't. This is the easy part, after all. The fun part. You can do this yourself. 
So you call up your buddy to cancel, and after he stops laughing he asks if he can help, and that's when you politely ask where he's been for the last week and a half while you were out in the garage until forever a.m. all by yourself leaning over a wet hood with a flashlight and a crumpled piece of 400-grit sandpaper. 
You can do it yourself. You just have to figure out how. There are several options, most of which we'll try to avoid. For instance, painting an entire car with spray cans has been done, so it's not necessary to blaze any trails in that particular direction. Other creative attempts at applying paint to a car have also been perfected, like using a paint roller, so no need to explore those areas either. As it turns out, the traditional automotive refinishing method of firing tiny globules of paint from a pressurized gun is still the best. It's also in fact the easiest. 
What, you say? Easier than Krylon? How is that possible? What could possibly be easier than rattling a metal can for a few shakes and dumping its contents onto a pristine hood or fender, then tossing the empty into the trash bin? That actually is pretty easy, but here's the difference. A spray gun nozzle has a hole about 1.3 or 1.4 mm in diameter. The hole on a rattle can nozzle is about a third that size, or about a tenth the area. The spray gun has enough pressure to atomize all of that paint at a fairly high viscosity. The rattle can doesn't. The simple fact that a spray gun can apply paint thicker and ten times faster than an aerosol can should be enough to convince us. 
So what do we need? For starters, we need a compressor, one that's big enough for the job. Anything used for air tools should be more than adequate, but it's still a good idea to compare the requirements of the spray gun (in cubic feet of air per minute or CFMs) with the output from the compressor. Modern HVLP (high-volume, low-pressure) guns need a huge amount of CFMs, but you can get LVLP guns that work almost as well at much lower CFMs. You have three options for getting the equipment. You can either already own it, which is awesome, or you can buy it at your local hardware store, which won't be as cheap as a Maaco special, or you can borrow it, which is almost as awesome as already owning it. You can also probably rent these things, but that would be four options. 
Painting is an exercise in patience. Paint has this unfortunate need to dry, and it's not quick about it. Paint also doesn't react well to being handled before it's dry. So the most important thing we need to know about painting is that we are not patient people, and without self-imposed restrictions we will make a mess of it. I'm not sure if impatience is a character trait of all people or just Miata owners, but there it is. 
What paint do we use? Good question. I like black. You might have other ideas. Because we sanded our Miata down to the nub, we probably have many parts of the car that are a veritable cornucopia of colors. We may even have bare metal, which is as bad as it sounds. So we're going to paint the car first with primer, at least parts of it, which will ensure all kinds of good things, like better paint adhesion, better rust protection, and better color uniformity. There are many different types of primers for different types of painting and different types of things being painted. We're painting a car, which narrows it down a lot. We want a sandable automotive primer. We want a lighter color like gray if we're painting a white or yellow car (or a gray car, duh), and a darker hue if we're painting the car a more appropriate and pleasing color like black. 
I'm not a huge proponent of shooting the entire car in primer. Some people like to do that, to put down a good base for the color coat. To my mind, the car already has a nice protective coat of primer in most places, courtesy of Mazda. More primer is just extra weight. We do want to make sure that any unprimered spots, such as the aforementioned bare metal, get a coat of primer, as well as any areas with major color changes. For these areas, I think it's really okay to use a good quality automotive primer from an aerosol can, and just a couple of light coats. Wait half an hour for that to dry and wet sand it lightly with 400-grit. 
So now you're ready to go. As soon as the weather's nice. A good day for painting has fair temperatures and a cloudless sky. Sixty-eight degrees Fahrenheit is considered a minimum. Maximum is whatever you can stand, but with heat comes humidity and that can cause any number of problems with the paint. 
There seems to be some debate over which Miatas were painted with a single-stage color, and which were shot with a base coat and clear coat. I'm sure the answer can be found somewhere, but unless you're looking for concours points, I would always opt to go with a two-stage paint. It's a tougher paint, and it's easier to get a better-looking finish. A gallon will be more than enough for three coats of paint on a Miata. You can probably do the whole job with 3 quarts of color and 3 quarts of clear. That'll add around 6 pounds to your Miata, less whatever you sanded off earlier. 
You can buy paint in any color and quantity from a local automotive paint supplier. They're all over the place, but usually well-hidden in industrial parks and strip malls where no one ever goes. They normally deal with body shops, and they'll spot you as a rookie the minute you walk in, but they'll also be helpful and friendly and will sell you at least as much of everything that you need. Look up your color code on (or the door jamb of your Miata), and ask for acrylic enamel paint for a Mazda with that color code. 
There are other types of automotive paints besides enamels, but I like enamel. Acrylic enamels are easy to work with and they cover better than lacquers, so they need fewer coats. There are other types of enamels, but acrylic is cheaper. If you prefer lacquer, find a painter who likes lacquer and go read his blog. Okay, that was harsh. Sorry. 
Automotive acrylic enamels are mixed with other chemicals just before use. The instructions for what to mix and how much to mix will be on the paint can label. Color (base) coats sometimes just need a reducer (thinner), and sometimes a reducer and a hardener. Get some plastic paint mixing cups with gradations on the side so you can mix the stuff as accurately as possible. Usually you have a long time to shoot the paint after mixing, several hours at least, but don't waste too much of it. Be sure you're all ready to go before mixing, with the car prepped, drop cloths over everything in the garage, compressor on, gloves on, and spray gun at hand. Your respirator should also be nearby. If it's not obvious at the first whiff, these are chemicals you don't want to be breathing too deeply. 
Spray guns all work pretty much the same, and have only a couple of adjustments for air pressure, fluid control, and pattern control. A million videos on YouTube can show you the details. It's always a good idea to make your final adjustments while shooting on a large scrap of cardboard, before you spray the car. That way you have a feel for how much paint is coming out and where it's going. If you've only ever used aerosol cans before, a spray gun isn't a lot different. Keep the distance to the work about the same, maybe 6-10", and keep the gun moving. It's best to start and stop the gun to the side of the work, not directly over it, but the main thing is to squeeze the trigger only after the gun is already in motion. 
Because the gun uses a fan pattern instead of a spray can's dot pattern, it's more important to keep the fan perpendicular to the surface you're spraying. That's fairly easy to do on fenders and doors, less so on really curved things like Miata bumpers, and horizontal surfaces like hoods. But do the best you can. More arm motion, less wrist motion. Watch YouTube videos. 
Before you shoot any paint, it's a good idea to wipe the car down one more time with a tack rag to get rid of the latest dust buildup. A tack rag is a piece of cheese cloth with some sticky goo attached to it. You can buy them at the paint store. Prepare the tack rag by first unfolding it completely, and then ball it up into a lufa-like shape and consistency. Wipe the car softly so you don't get any sticky goo on it. As soon as you're done, plug your spray gun into the compressor, pull on your respirator, and start painting. 
Just like with aerosol cans, Your first coat is your adhesion coat. You're not looking for much more than basic coverage, and the paint shouldn't be too wet or too thick. Let it dry for the prescribed time, usually around 15 minutes, and then shoot a thicker coat. This second coat should really be pretty wet, with all the paint flowing into a shiny film. Years of shooting paint from spray cans will make you leery about putting on too thick a coat, and that's good, but this paint is much thicker than the stuff that comes out of cans, and drips won't be a problem. Sags are more likely, if you get too much paint in one place. That'll look like the surface of an orange peel as the paint starts to dry, but will be less noticeable by the time the paint flashes. 
Time between coats varies for different brands of paint. The paint store should've supplied you with a technical data sheet for the paint you bought, but if they didn't you can always get one online from the paint manufacturer's website. 15 minutes is typical. With base coats you can usually tell it's time for another coat because the paint starts to lose its gloss. With clear coats you really need to use the manufacturer's recommendation. With automotive paints there is no sanding between coats. The only exception would be if you made a total mess of some area and you needed to fix it. Otherwise, shoot the next coat directly over the previous one. 
You need to decide after the second color coat whether or not you want to shoot a third. It's usually a good idea, but if you really nailed that second coat and the color looks uniform everywhere, you can skip it. Wait at least half an hour after the last color coat before you shoot the clear coat. You can wait longer if necessary, even overnight, but within a couple hours is best. You can use that time to clean the gun and mix the clear paint. Shoot the clear the same way you shot the color. First coat is for adhesion, not too thick. Second coat goes on wet, 15 minutes later. Again, decide whether or not you want a third coat. If the car looks brilliant at this point, you're done. 
Final Touches 
Don't leave masking tape on too long. It's good to remove it before the paint dries so you're not trying to break the paint at the edge of the tape. 15 minutes after shooting the last coat is not too soon, just be very careful that anything you pull off doesn't end up falling into your fresh paint. If it does, you can carefully extract it and probably fix the area in a week or so, but it'll bother you the whole time. 
If you can, leave your freshly-painted Miata in the hot sun the first day. During the first 24 hours the paint will be dry, but soft. You can leave a fingerprint in it if you press too hard. After 24 hours the paint gets considerably harder, and after a week it's tough as nails. I'd wait another month or so before doing anything drastic like striping the car, but you can certainly wash and wax it after a week. 
Unless your garage is a stage-4 clean room, the clear coat is likely to pick up tiny specs of dust as it dries. You won't be able to see them, and the paint will still be totally glossy, but in a week or so when the paint is fully cured and you can rub your hand over it, the surface may not feel silky smooth. For most of us that's not an issue. If it is for you, wet sand the surface with 1500 or 2000-grit sandpaper, then rub it out with successively finer rubbing and polishing compounds. I don't recommend this because it's a lot of work, and it doesn't feel right taking sandpaper to glossy new clear coat, and most people wouldn't notice the difference anyway. 
Obviously there's a lot more to painting a car than we can cover in a short blog. Or even a long blog. We didn't cover body work at all, and it wouldn't surpise me if we missed a few other critical steps. But painting is not a big mystery. People do it all the time, and everyone who has, had to do it the first time once.
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Comments (newest first)
2011-08-25 07:35:07 from MiataKnowBetta your writing style!!! 
I can only add one tip. At the aforementioned paint supply ask if they know any local body shops that rents booth time. Shooting in a booth can really ease the work load from a standpoint of "garage prep". 
You still need to have all the supplies, paint, and gun...but you have the advantage of a really nice compressor putting out dry, clean air. A closed, filtered, ventilated and well lit space really helps in getting the final prep done right. It is all about getting dirt out of every nook and cranny because when the paint gun hits the N&C if it isn't clean that dirt will join your paint. The final two steps before spraying....air nozzle on the hose, booth closed and fan on...start at the front of the car (assuming you didn't back in to the booth) and blow all those N&C's from front to back. The booth airflow will take that airborne dirt away. Last last tack cloth to pick up any heavier crud that settled out. 
If you get lucky, as I have, you'll find a gem of a guy that rents his booth AND loves to give pointers. For me the $100 for four hours of booth time are worth every penny. 
I guess that was more than one I'll throw in another. If you want a nice quality paint job but aren't concerned about show quality or historical correctness, take a look at TCP Global ( ) I have been very satisfied with their paints and the prices can't be beat. Even the owner of the paint booth I use has been impressed with the paints I've brought in.