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..................- Bodywork & Painting Page 1 -
I've put these pages on the site to help others who might not have a lot of experience with body work and/or painting. What I offer here is what I've learned from others; books; and on my own. Remember there is usually more than one way to do something and still have it come out fine. I'm trying to show how a novice might over a course of time repair and paint his specialty car using common inexpensive equipment (relatively inexpensive) in a home garage/shop. The following is what has worked for me, but I'm always looking to improve, so I'm open to suggestions. Sum
................................................................- Initial Thoughts -
Where I live you can take a panel down to bare metal and if it is inside you won't get any surface rust on it over a period of time. If you live in an area where you will get surface rust then I would work on one panel at a time. Taking it to bare metal, doing the body work, and then priming it with the first coats of primer. I would do all subsequent coats of primer and block sanding when you have all the panels ready for the top coats (base color coats and clear coats in my case). This method of working on one area of the vehicle at a time is probably best no mater where you live as you then don't feel so overwhelmed. Now if you are doing drastic customizing similar to what I did you might want to do all your major cuts and tack everything together to make sure that you have the look you want. Then final finish one panel of the vehicle at a time. These are just suggestions.
Equipment Tip: If you are going to be painting a whole car you are going to need probably at least the following: 5 hp. single stage compressor (2 stage would be much better, but I got by with this as my HVLP gun doesn't need a lot of air and I painted things apart); Spray gun that doesn't need a lot of air or a large compressor and one that can produce a good job (see my suggestions later); sanding boards (long, medium, and a couple of rubber sanding blocks (hard & soft); mig welder if you are welding in patch panes and/or customizing; air die grinder, 4 inch electric grinder, air cut-off wheel (all of these to finish your welds up and to install patch panels). The following would be nice, but not absolutely needed: DA sander and a low speed or variable speed buffer/sander. I would stay away from a long board air file and other air sanders even the DA until you gain some experience as they can get you into more trouble than they are worth and your not a production shop. If you don't like sanding stop right now and find something else to do with your time, because you are going to be doing a lot of it if you want a good job.
Spray guns: I've had the HVLP gun from Harbor Freight (number 38308) that I had bought for doing primers for a couple of years. I found out that it will spray the base and clears to my satisfaction also. I would also check with Len at his Internet Auto Body Store for his recommendations. His Sharp Platinum would probably work fine also. These will both work with a small compressor. A top of the line gun like a Sata is great, but it puts out a lot of paint, like a body shop needs for production work and a fine finish but since it puts out so much paint that can get a novice into trouble if his gun technique is not great (read runs -- but runs can be fixed). Due to it's air requirements (read large) it also needs a 2 stage compressor. I would love to have one though someday. Remember if you are going to color sand and buff at the end you can live with some orange peel in the finish paint. The gun I'm using produces very little if I use it right and even though I haven't color sanded yet I could to get a truly outstanding final finish.
Your Health: I finally bought a supplied air hood from Len at his Auto Body Store about 2 years ago. I wouldn't paint without it now. Not even the primers. The paints I'm going to talk about are all 2 part paints, except the base, and can be VERY DANGEROUS. Don't let this project kill you now or shorten your life get a supplied air system. I used a charcoal mask for a long time and am still alive, but these just don't get it even with new canisters all the time and I might pay down the road. These paints aren't like the ones that were used even 15 years ago. They are dangerous, period. One of these systems will cost you from about $350 to $450 depending on which you get. If you are broke do like I did and buy a cheap gun and put your money into saving your life. Remember you are not painting in a spray booth that moves tons of air every minute through the booth. At least spray the primer with your shop open and new charcoal canisters and as much air as possible moving through (not easy in the winter) and also not possible when spraying the sealer, base and especially the clear.
Wear a dust mask while sanding and grinding. Wear a face shield while grinding. Wear ear protection while grinding. Get an autodarking hood and you will be a better welder (I got a nice one from Harbor Freight for about $50 that has adjustable shades and more importantly a lens that is big enough for me to see out of with my bifocals).
I wear gloves all the time. The cheap white cotton ones will work great while sanding. They keep your skin oil off the surface and you can actually feel the surface better for highs and lows with them over using your bare hand and they protect you from the sandpaper. I wear latex gloves (I buy them by the 100 from Harbor Freight) while using the bondo, the cleaners (oil and wax remover -- PPG 330), and while wet sanding. You will do a better job with the gloves on.
So now let's get going.
.............................................................- Pre-Bodywork Prep -
All the work I've done on my truck and teardrop trailer has either involved taking the metal down to bare metal or using new metal. I stripped the frame, suspension, small pieces, and most of the body by sandblasting. If you use this method you have to be extremely careful of the body sheet metal so it is not warped. I made a pressure blaster, but for a home shop I would probably now buy Harbor Freight's pressure one that is often on sale for less than $100. I used what is called blow sand (blows around the country here) that is native to southeast Utah. It is extremely fine and not very aggressive so be very careful with commercial sandblasting sand. Now I use a stripping wheel to take body panels to bare metal and that would be my recommendation. Eastwood Company has these disks and they look kind of like scotch pads and you can use them in a drill, air drill or a grinder depending on type. They will leave the surface in about the same shape as worn 80 grit paper which is about right for primer. Others use 80 grit sanding discs and Len has these in a convenient hook and loop configuration on his Auto Body Store. If you strip a panel at a time and work on it you will get by this step as boring as it is.
All bare metal that is to be primed should have some tooth to it and the scotch pad type discs and/or the 80 grit will achieve this. If it is new metal like I used to build my bed and teardrop then you need to at least hit it with 180 grit to give the primer something to get hold of . Now any areas that need bondo I would hit with 36 or 40 grit discs as this will give you a good surface for the bondo to grip. Don't get carried away with these discs as they can remove metal and make the panel thinner.
..............................................................................- Bodywork -
First let me talk about primers and bondo for a minute. I've used PPG primers on my projects and Dupont top coats with no compatibility problems (see following for which ones). I like the PPG products better for a home repair environment, but they are 135 miles from me and Dupont products are 70 miles from me, so they are quicker to get to if I need extra during painting the critical top coats. There are a lot of good brands of paint on the market, but these are what I've used. I will probably use PPG all the way through in the future as I believe some of their products are a little better for a rod and a home painter than some of the other brands. None of this paint is cheap, but you're not buying it every day like a production shop and you probably want your project to get the best.
Next, with some of the new primers (not the high build) you can put the bondo on top of them. For my type of work I don't do this. The main reason is that the PPG DPL40 primer that I like for the foundation coat has to be topcoated within one week with either bondo, a high build primer, such as K36, and/or the base and clear. Now if your working on your vehicle as a hobby you probably can't meet this time frame. If you don't, you have to scuff or sand the DPL40 and then apply more DPL40 and top coat this within a week. For this reason I like to do it the old fashion way of taking the metal to bare metal; applying the bondo; then start with the primer coats when I can put the DPL40 on and then topcoat it with K36.
Okay, at this point we have a panel that needs to be repaired and it is down to bare metal and the area that needs bondo is roughed up with a 40 grit disc. Also the area is relatively flat after hammer and dolly work if that is needed. I don't like the bondo to be much more than 1/16 inch, but to be honest I have quite a few areas that are 1/8 inch and maybe a couple that are thicker than that. The more bodywork you do the better you'll do so don't be too hard on yourself. I have over 130,000 miles on my truck as of this writing and none of the bondo has fallen off yet (I finally do have some stress cracks due to the fact the truck is almost totally welded together -- fenders moulded to the bed and body, etc. -- and that can create stress cracks over time). I think some people make to much of finishing with no bondo and that keeps a lot of people feeling they can't do their own projects.
Bondo Mixing Tip: I like to mix my bondo on a piece of flat glass. I use an old side window from my truck. It will not absorb any of the bondo (don't use cardboard) and is easy to clean. I put a ball of bondo on the glass and a proper length of the hardener next to it. I use two of the yellow spreaders about 4 inches long to mix it. Use one and then use the other to wipe it off the first back onto the glass until mixed. After putting the bondo on the car I scrape any left over off of the spreaders and the glass with a 1" wood chisel. Then I take some paint thinner on a paper towel and finish cleaning the glass, spreaders, and chisel. Believe me if you keep all of this clean you will do a better job. If not you will get chunks of old bondo in the new on the car and if your spreaders aren't clean and straight edged you will drag grooves in the new bondo as you spread. (Note: these type of tips are going to make this longer, but I don't see this stuff mentioned in the books and it can really help speed the process up and make it less frustrating, so bear with me or skip over my tips).
I spread the first layer (if it is a large area that is going to need a lot of work) of bondo on relatively thin and IN ONE DIRECTION PRESSING THE BONDO into the scratches on the metal. As soon as this sets I hit it with a long board that has 40 grit paper on it. Get the bondo at least a couple of inches past the repaired area. Don't be afraid to get a large area covered with the bondo. You will be sanding most of it off. If I was doing say a fender from a 30's car that was okay, but still not perfect I would cover the whole fender with a skim coat and proceed.
Cheese Grater Tip: I don't have much luck with the cheese graters to shape bondo that hasn't quite kicked. Work on shaping the bondo with the spreaders and you won't have much trouble just using your sanding boards to shape the bondo.
Sanding Board Tip: I have two long boards (mine are a yellow plastic and have a bottom that you attach a long piece of sand paper to (already cut for this)). I keep one with 40 grit on it and the other with 80 grit on it at this stage. I also have two medium length boards of about 8 inches long (one for 40 and one for 80 -- they take sand paper that I rip to size from a full sheet and clips on the end that hold the paper. I also use a couple of rubber sanding blocks that are about 5/8 inch thick and about 2 X 4 inches. One is hard and the other is black on one side (medium hard) and white on the other side (soft). I also have misc. pieces of rubber hoses of different diameters that I can wrap sand paper around. Don't use your fingers (except in the smallest of areas) as if you do your surface won't be flat and that is what we want.
So with the first layer of bondo on you want to rough cut it into shape with the longest board (covered with 40) that you can use for the area you're repairing. Do all of your sanding in X type movements and change the direction of the X pattern constantly. You are really shaping and cutting with the 40 grit, don't worry about the sand scratches and let the paper do the work. Don't bear down. Work form the good parts of the metal into the repaired area. This will help you achieve the final shape. On a shape like a rounded fender side never sand along the fender line. Start by putting your board horizontal to the ground and grab both ends. Now sand in an X pattern from say the bottom right up to the top left going over the curve of the fender. After a couple strokes this way switch so you start at the bottom left and sand to the top right going over the curve of the fender. Don't stay in one place. As you are going up and down over the curve in the X pattern constantly move the X pattern to the front or back. You can take a long flat sanding board with paper on it and in this procedure work a shape with a curve like a basketball at this stage. Treat all curved surfaces in the same manner regardless of rather you're using the long board or a smaller block to sand. Remember we are shaping at this stage and not sanding. During the final sanding work in the same manner.
You will soon sand through in areas to the bare metal. Now you have a decision to make. Is the bare metal high (a bump) and need to be knocked down or is the surrounding area with bondo on it low (a dent/depression) that needs more bondo. If it is high take your body hammer and dolly and knock it down some (you probably need the dolly behind the bondo area and hit the high area until it is a little low or flat. The dolly will raise the low area as you hit the high area. Be careful of hitting the metal with the dolly directly behind it as this can stretch the metal and cause you problems.). In all of the areas that are sanded out and where the bondo stops the bondo should not have a definite line at the edge, but this should be a very tapered area with the area going from bondo to metal with no apparent edge.
Change your paper when it wears out. Don't force it or you will wallow the area out and have to keep applying more bondo. Don't sand the low spots. Sand the high spots down to the level of the low spots and if you hit metal or start going low stop and add bondo to that area and past it a little.
Now you are going to need for sure to put a second and maybe a third and fourth coat of bondo on the repair if it is a large area and you are doing this for the first time. You will get to where you finally have all the lows in the area filled and the area will have the proper shape. Stop just a little on the high side while doing this (about the thickness of your sand scratches).
Now I would put a very, very thin coat of bondo on the whole area. Just spread the bondo so you are taking it almost all back off with the same stroke. It is just to fill the sanding scratches and any pinholes you might have and you are not trying to build any thickness at this point (use premium bondo and mix it right and you shouldn't have pin holes). Now what I do next and a pro wouldn't do this, but it will help you and me immensely is to spray a guide coat on the area.
Guide Coat Tip: A guide coat is taking a contrasting paint that is a different color than the work area and misting that paint on the area. Spend a couple of bucks and buy a spray can of the type that is made for this. It will go on nice and you will be using it later with the primers. 2 cans should be enough for the whole project. Just mist it on. You'll see that you don't need much.
With this light guide coat on the area switch to your sanding boards with the 80 grit on them. Let the paper and the board do the work and sand the area flat. The guide coat should disappear along with the 40 sanding scratches. If it is still visible you have a low spot or a pin hole or scratch. Take a little 80 with you finger or block and sand the guide coat out of the low spot and apply more bondo and then more guide coat and then sand again. If you do all of this the area should now be ready for primer. Some people will now go over the area with 150 or 180 and some will use even 320. It won't hurt, but I don't do it as in the priming steps I'll end up putting a lot of primer on and sanding it off and it is designed to fill 80 grit sanding scratches. If I was latter just repairing a panel on the car and trying to keep the primer to a minimum then I would go to a 150 or 180 at this stage. You be the judge.
Hint: You can use the guide coat earlier in the bondo shaping steps. With it you can instantly see if an area is high or low. The more normal procedure is to run your hand (flat) over the area to feel them, but this can be tricky to get the hang of at first. Use the guide coat and don't tell anyone ;-).
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