This is a how to on the Prep and Paint Process. Taking place AFTER the bodywork is complete. And after dis-assembly. I am basing this article around the Sherwin Williams Paint line. It is the system I am most familiar with, and recommend. It is a very simple system and easy to use. This article can be used with other systems as they are all similar, but not 100% the same..
Ok, so you finished all the metal and bodywork...or your car doesn't need any bodywork, you just want to refinish it... now what? Pay a pro? Or do it yourself? If you opt to do it yourself, follow these steps and you can achieve the finish you desire. With lasting results..
Step 1 - Self Etching Primer
If your car has any bare metal spots that have been bare for more than a few hours, lightly sand them to remove any surface oxidation. Sand the remaining parts of each panel with 180-220 grit to ensure that it will stick to any pre-existing primer or paint that you decided not to strip. Stripping a panel entirely is not necessary unless there are multiple existing paint jobs on the car already, or the pre-existing paint is badly damaged or failing. Many people don't realize that paint sticks great to paint. Spray these bare area's with 2-3 coats of a self etching primer such as G.B.P . This product is available in quarts, gallons and aerosol's. It is a two part primer in which you will need This Reducer . It is mixed 1:1 . It does not use a hardener. Which means you can leave it mixed and use it when u need it. Very convenient. Allow 5-10 minutes between coats, or until is has "Flashed". Flash is a painters term for in between coats. Also called "Flash Time" . When you spray this product, it goes on wet. In a few minutes you will see it has dulled or appears dry. That means it has flashed. Flash time will depend on temperature, humidity, and application.
Step 2 - High Build Primer Surfacer
Now that all your bare metal is taken care of, it would be a good idea to use a High Build Primer Surfacer. This is a thick primer which can be used to fill in any scratches that remain in the bodywork, slight waves, and even minor dents. This process is a must for cars with any kind of bodywork done. You can choose to only coat the bodywork areas with it, or coat the entire panel or car. But being that most people reading this are doing resto's, im going to say its best to do the whole car. That being said, spray 3-6 coats of a High Build Primer Surfacer such as Spectra Prime. If the bodywork is a bit rough, it is not uncommon to put more coats. If you allow proper flash-time between coats, put as many as you need. 10 is not that uncommon. Even more if you need. Dont worry about mill thickness problems as most of the primer will be sanded off during the blocking process.
Allow 5-10 minutes flash time between coats. Or even more if needed. I usually go by the hand-slick method. Run your finger across the masking paper near where you just sprayed. If it smudges, wait! Applying too much primer too fast can result in solvent-pop (tiny pockets of solvent that cannot escape and evaporate during the drying process). These are a nightmare to get out.
Besides the primer surfacer itself, you will also need Hardener and Reducer. Sherwin Williams system reducers are compatible with most of there products. They go by numbers. 1-6. 1 being for cold temperatures, and 6 for desert temps. So the reducer you use for your primer, you can also use for your clearcoat when it comes to it. This primer is mixed 4:1:1 . (4 parts of primer, 1 reducer, 1 hardener).
Step 3 - Guide CoatA Guide Coat is what most beginners do not know about. Its a sort of trick of the trade. A guide coat is an EXTREMELY LIGHT coat of an opposite colored primer from your high build primer. For instance, if you sprayed light gray primer, get black for your guide coat. If you sprayed black, get light gray for your guide coat. If you used a different color primer all together, just get something you will see clearly for your guide coat. You will only need one aerosol can of it for a whole car. This coat will show you your High and Low spots while blocking your primer. Now walk around the car and spray the lightest coat you possibly can.
The following is an example of how the guide coat should be applied. You basically are applying 1/4 of a coat. Very light. Pretty much just a dusting.
Step 4 - Blocking
You will need an assortment of sanding blocks for this step. A Long Board, Short Block, and a Soft Block. Obviously the long board is for large areas, short for small, and soft is for curved areas such as around wheel openings and such. Lets say your starting with your fender. Grab your long board and put some 180 grit paper on it. Starting with the largest area of your panel, start sanding on a 45 degree angle. Moving back and fourth, up and down at the same time. Keep the board parellel to the ground and sand from top-left, to bottom right...then back. Working roughly 1 1/2 square feet at a time. Changing directions frequently, kind of an X pattern. The guide coat will show you scratch's, high spots, low spots, pin holes, and any imperfections that exist. Simply put, if the sandpaper doesn't reach the guide coat, that spot is low, and will remain the color of the guide coat. If the guide coat disappears in one spot really fast compared to the others, its high and the board is not making contact yet with the rest of the panel. Sand until its all even. Apply more guide coat i you need to double check your area. If you sand through the surfacer, its ok. You can hit these spots with more primer later. Use the soft block on curved parts. Do not use a hard block. You will cut grooves with the edges of the board or give your curve a hex shape. After your finished blocking with 180, reapply primer to the areas you sanded through. If its down to metal in a spot, spray some G.B.P Self Etching Primer on it, then apply a few coats of the High Build primer if desired. But not necessary. Once its dry, grab your soft bock with some 220 or 320 and go over the panel to remove the 180 scratches from the panel. Another guide coat could help with this if you like.
Step 5 - Wet SandingNow your car is all primed, blocked and ready to be wet sanded. Again, apply a guide coat. It may seam very repetitive. But simply put, guide coats don't lie. If there is an imperfection, it will put it on a platter and show it to you. It is probably the most valuable tool in the auto body industry. Get a bucket of water, a rubber squeegee, and put some 500 grit paper on your soft block. Do not sand with your bare hands if you are unexperienced. Your fingers could and will put grooves in your primer if done wrong. Dunk your block in the bucket and then start sanding. Direction is not crucial at this stage. Just don't go up and down, or stay in the same spot for too long or more than necessary. Wipe with the squeegee to look at your work from time to time. Same principle as the first blocking stage. Sand until all the guide coat is gone. Do this to all the panels.
Step 6 - Clean Up
Now clean the car of all the sanding residue, and other dirt and dust. This can be done with an air blower and wet rag. The best way to do it is to actually wash the car with a hose and good detergent, but if there are no windows in the car, or weatherstrip, this process is hard to do. So just blow, and wipe till you cant anymore. In every crack and crevice, 168 times. I cant stress this enough. Inside the jams, doors, down in the cowl...anywhere and everywhere. You don't want any dirt or water flying out of spots while your painting.
Step 7 - Taping
This process is pretty self explanatory. I cant hold your hand on this one. Get the tires off, get the car on jack stands and put tape and paper where ever you don't want paint. For a full paint job its best for the doors, hood and deck lid to be off the car so you can do the jams at the same time. Eliminating tape marks. Just set them up on stands. Also, wet the floor to hold down any dirt or dust that could possibly get airborne if hit with air from the gun.
Step 8 - Clean Again
Go around and blow and wipe again. Wipe the car down with a Wax and grease remover. Such as Ultra Clean and Aqua-Mate. The oil from you skin is all over he car from the tape process. As well as other contaminates. Its best to use both. The ultra Clean will remove wax , grease and oils..while the Aqua-mate will remove all water-based contaminates. Apply with a spray bottle or rag, and wipe with another rag. CLEAN RAGS!
Step 9 - Sealer
This step is optional. If you were painting directly onto an old paint job, or blending, or there are scratches from sanding that you didn't bother to sand,you should seal it. But if you followed my steps correctly, all you should have is 500-600 grit scratches. Which you can paint on directly. The Spectra Prime which I stated above for the High Build Primer Surfacer, could be used as a sealer by mixing it differently. You would spray one wet coat, then go right into your basecoat when this coat tacks up.
Step 10 - Mix your Paint
Sherwin Williams, as most other basecoats, are mixed 1:1 . One part paint, one part reducer. Make sure you paint is mixed really well. If you put a stick in the can and have solid residue on the bottom, keep mixing. You will need Basecoat Stabilizer aka Reducer. Mix roughly half the gallon at a time. You don't need to mix it all at the same time. You have as much time as you need between coats to mix more. It has a 24 hour window.
Step 11 - Final Prep and Basecoat Application
A Gravity Feed HVLP spray gun is best. But not necessary. Neither is an expensive gun. I have a $60 gun made in china that sprays very well, almost as good as my Sata. You will also need a Pressure Regulator with a Gauge, a Water Separator/Filter and obviously a compressor. You need a big enough compressor so you don't get "Line Drop". Line drop can cause drastic inconsistency in application. Which you do not want. The key to a successful paint job is consistency. Some other key items are a respirator , paint sticks , paint strainers , a paint suite and tack rags.
Fill your gun and tilt it to the sides to assure that no paint is leaking out the top. If it drips while spraying it can be a hassle. If it drips, wrap the cap with some masking tape. Set your air pressure coming into the gun at about 25 psi. Adjust your needle all the was out, Pull the trigger and adjust the needle in until you feel the trigger push out. Once you feel it touch, adjust in 2 1/2 turns and lock the nut. Pull the trigger and check your fan, spray a piece of the masking paper to check it if you have too. You want it all even, no dead spots. If its not even, your gun is dirty. Go clean it and start over.
If everything is good, put your gun down. Get away from the paint area and blow yourself down really good. You hair, your clothes, your hands, respirator and anything you can. Even your gun. Cleanliness is key. The guys in my shop say Im nourotic..lol.. But my paint jobs come out really clean.
Now that you know your clean, go back to the paint area and wipe it with wax and grease remover again and blow it off. If you have an exhaust fan, turn it on to suck out whatever is airborne. Now get out of the area again and blow yourself off...yes, again. Whatever was on the car could be on you now.
Go back in the booth or paint area and tack off the car with your tack rag. Your ready to paint..
This part is entirely based on style of painting. And varies from painter to painter. I start from the bottom corner and walk down the entire side of the car working my way up. Keeping the gun at about 6 inches from the panels, overlapping 1/2. Kind of like cutting a lawn. When i get to the top of the fenders and quarters, I go up the sail panel, across the roof to the middle, then go entirely across the trunk and the back, go to the hood and come all the way across, to the other half of the roof then down the other side. Going down. The way you do it is really not that critical with basecoat. But with clearcoat, you have to take into account the tack time. If you start at one point, by the time you clear everything and finally come back to the point you started, that spot could already be starting to tack up. Therefore it will look like overspray there when you spray over it.
Spray about 3-4 coats of basecoat with about 10 minutes flash time in between. More coats may be needed if it is a transparent color. Transparent meaning its not covering well. Some paints are like this, it does not mean put the paint on heavier! If your doing a full paint job, by the time you finish the last part, you can usually start the next coat at the first part right away. Tack the car off in between coats. You DO NOT SAND between coats of basecoat as many people think. Although after the car is covered with base, YOU MAY go around with a piece of 1000 grit and sand out any dirt nubs that may have gotten into the paint job. But spray some base over it when your done.
Your now ready for clear.
Step 12 - Clearcoat
For clearcoat in this article, were going to use CC-639 . It is the best Sherwin Williams clearcoat in my opinion. This Clear offers a one coat technique which you should not try if you are inexperienced with the product. The basic technique is a two coat application. But on a full resto I would do 3. But DO NOT go more than that. The most common misconception is that more clear is better. WRONG. Too much clear can cause clear shatter. Another misconception is that you sand between coats. NEVER. Those days are long gone. To use this clear you will also need Hardener and Reducer . That is #3 Reducer. As I stated above there reducer system is universal. 1-6 . Select the reducer based on you temperature. Going a little slower on the reducer is a good idea. It will give you more time to work. This clear is mixed 4:1:1 .
Clean your gun very well with lacquer thinner before filling it with clear. Take a walk around the car and make sure you got everything covered with base. Under the rockers panels, wheel wells ect..If all is good, tack it off really good with an unused portion of the tack rag.
Apply the clear in the same manner as the base, but put it on wetter. It may be a good idea to practice on an old panel to get a feel for how it flows. Too dry will cause excessive orange peel, too wet will cause runs. I personally get a little closer with the gun, and move faster. Flows out nice with this clear. I also boost the pressure up a bit to about 35 psi. And I back the needle out of the gun 1 turn.
Apply 3 coats allowing it to become hand-slick between coats. You do not tack, sand or do anything to it between coats. Walk away. Your done..Wet Sanding and buffing
This clear can be buffed in high production shops in as little as a few hours. But it is best to wait as long as you can. A month would be best. I know its a long time, but paint is not fully cured for about this time. It will be releasing solvents for this period of time. That's how it cures. Dry=Shrink. You did all this work. Wait it out. You can wash it, drive it and do everything else. But no wax, and no buffing. It will require more elbow grease to buff it, but it will be worth it. Trust me.