I'm going to repaint my 86 F-150 with acrylic enamel in my garage. I painted another truck two years ago with pretty good results. I did that paint job totally according to the directions.

I'm wondering if its absolutely necessary to use the primer that comes with that paint. The reason being is that I have replacement used (rust free) fenders, hood, doors and quarters (new), and I'm going to paint them before I put them on the truck. Then, when I have the truck re-assembled, I will do a final coat altogether.

Or, is it a bad idea to paint them off the truck? Should I just paint the backsides, assemble the truck and then do a final coat? Can I do a coat of paint overtop of what paint is already there, or does the primer help bond the paint to the metal, and any paint that is still there? Not looking for a show quality finish, but I'll probably buff it when I'm done. I would rather use rattle can primer on each panel as I work with them, then have to use that expensive stuff. So, I'm basically trying to save some money.

There are no dents in any of the panels, there is only one fender and one door that I used glazing putty to fix a few small door dings, the rest of the panels are flawless, but still have paint on them. They are different colors than what I'm going to use in the final coat. Does the primer also help to cover up these different colors? I seem to remember when I painted the other truck, that after I primed, I found a few spots that needed more glazing putty, and I did not prime over them, just painted them. They are absolutely unnoticable.

Thanks for any tips, I'm still an amateur, although that first truck I did looks as good as any paint shop job. Looking forward to another one.

 

If you are going to paint over existing paint that is in good shape then you can just sand that paint with maybe 320 to scuff it up. If the panels are different colors then what happens will depend on the color you are going to use. A dark color just might hide those different colors pretty well as compared to Wimbledon White. If there is no bare metal then you won't need a primer but if there is then an epoxy primer would be best. PPG's Omni MP epoxy primers are almost as good as their DPLF but at half the price at least. Maybe $27 per quart vs. $48 per quart for DPLF. You can also use the epoxy primer as a sealer by adding some reducer to it and you can seal off the old paint and have a uniform color to paint over.

As to procedure I am painting my 65 F-100 and every piece of the front has been removed. Since the fenders were originally painted on the backside by Ford I wil do the same. After all parts have been painted then I will reassemble the front clip carefully. However, when it comes to the cab the doors will stay on while the two windows will come out. Don't need the headache in trying to re-align doors. Later the box will come off and be painted by itself. You mention rust free fenders. How do you know they are absolutely free of any surface rust that you can't see yet? I don't take that chance so I coat everything with Picklex 20 to make sure there is no rust and then prime. A little rust, especially with no epoxy primer, is a little time bomb waiting to pop out.

 

You are right, they are not absolutely rust free on the backside, its just starting. I will be coating them with POR 15 to stop any rust and prevent any more from happening. The front sides are perfect.

Unfortunately, one of the fenders and one of the doors is stripped to pretty much bare metal, so I will have to prime those. I'm painting the truck a two tone gray/silver, so it should not have a problem covering up different colors. One door is white.

How about the black paint on the new quarters? Its inside and out, I'm going to POR 15 the inside, but is that paint ok to leave on? The fender that I stripped was hard to strip as it seemed that the black paint underneath was on really good. Unless it was just the crappy stripper I was using. If I have to, I will strip the quarters, but I don't want to if I don't have to.

 

If there is just a little surface rust I, myself, wouldn't use POR 15. Don't particularly care for it, think it is overpriced and besides it is for sticking to a rougher surface and not a smooth surface. You could go to a hardware store and find a bottle of Ospho which can be brushed on lightly and left to dry as per instructions. This will neutralize any surface rust and then hit it with a primer. If I wanted black I would use either the DPLF or Omni in black with 2 coats and have no worries from then on.

That black paint on the fenders you mention is Ford's baked on primer. Just picked up a very good 1968 Mustang rear valance and it still has the original black paint and service part number on it. I'm leaving it as it is when I paint the front and install it. The car never sees rain anyway. Yet, if it did, I wouldn't use POR 15 on that flat smooth surface as I could pop it off by bending the panel from lack of bite. I'd hit it with black epoxy satin primer instead. Since it is also on the front you will have to address that when you paint. All epoxy primers have windows in which the topcoat must be laid before you have to scuff and re-shoot another coat of primer for the chemical bond. You could scuff the panels in question so the enamel has something to grab onto assuming the black primer isn't so thin you scuff through it. I'm just being **** about it since I wouldn't want paint peeling off 1 month later or 16 months later.

 

Tbm pretty much has it covered. Like mentioned, a primer should be used over bare metal, paint is not designed to go over it. If painted and adhering fine and in good condition, you really wouldn't absolutely have to prime, but if you have a lot of different colored spots, its often advisable to prime or seal everything so its all one color before paint. Not only will it lessen the chance of any sort of reaction between old and new, if you paint happens to be a poor hider, it can save shooting a lot of extra coats to get coverage.

Epoxy is about the best for baremetal, many others, although they will work over baremetal, aren't really recommended as a direct to metal primer. Epoxy will stick well to properly sanded and prepped bare metal, and has good compatability, provide good corrosion protection, and will seal, whereas other primers are somewhat porous.
In a rattle can, is going to be lacquer primer. Back in the day it was used, as it was all they really had, but today there is so much better. It is not really recommended for use over bare metal anymore either, and will provide little protection. If metal is covered with lacquer primer for protection it can start rusting underneath just from the humidity in the air, this won't happen if epoxy primed.
Primers are cheap compared to paint, best not to skimp in this area, or on other things like cleaners, reducers ect, as they will create a good long lasting durable base for the paint or lessen the potential for a problem. Plus your labor has to count for something, might as well try to take the steps to make it last as long as possible. Same goes for cheap 1k spot putty in a tube, junk and shrinks. Your far better off using and spending a bit more for 2k spot puttys and fillers with a hardener. Just be sure to protect yourself properly when using these chemicals, All of it can harm your health if you don't properly protect lungs, eyes and skin and provide proper ventilation.

I feel the same way about rust convertor products like por 15, and as far as I know require rust be left to work. I know some areas are difficult to completly rid of rust, but I feel much more comfortable when able physically removing all rust and epoxy priming, then leaving any rust lurking underneath thats always looking for an opportunity to continue and keep growing.

As far as painting pieces off, thats fine, just make sure everything fits before hand so you don't end up with a painted piece you have to fight to install. But would only recommend it if a solid color. If a metallic or pearl it is best to jamb the pieces and install and paint all at the same time, or at least position the way they will be installed on the car and paint everything at the same time. If anything changes, temp, humidity, how mixed and sprayed, its very possible to have a color mismatch if shooting a metallic.

 

This is all excellent advice, thanks for taking the time.

I will definitely prime the whole works, why mess around.

It is a metallic paint, so what I would like to do is paint what I can off the truck, then assemble and put a final coat on the truck. Is this a bad idea once the first coat has dried?

 

Well if an acrylic enamel, you have to watch your recoat times, or you could have lifting problems. You would definately want to activate.
I would just get everything primed and fixed and in primer to the point of final sanding, then jamb with color and install- or position as will be installed on the vehicle. Then final sand, sanding off overspray. Do a good job taping up the already sprayed insides.

If you haven't done a lot of spraying, a single stage enamel metallic can be a challange. You will have to spray even without blotchyness or striping. If you do get uneveness, then you have to time it right, spray a panel, move to the next, then go back to the previous panel and shoot a mist coat to even it out (While its still wet enough to accept the mist coat so it keeps a good gloss, but has set up enough that the mist coat will no longer contribute to mottleing) Basically a lot of jumping back and forth between panels.

I shot a few ss enamel metallics back in the late 80's early 90's, including my moms pontiac 6000 using centari with the ultra performance pack (hardener). Really did look nice, but was a little tricky to spray, and I would say enamels are a little more difficult to spray then a urethane. Mom got in a pretty bad accident (lots of rehabilitation and still hobbles a bit to this day) not too much longer and totalled it. She has pics of it somewhere sitting in the salvage yard, all glossy, but with every panel smashed and they had to use the jaws of life to get her out. So needless to say, I wasn't able to see how well it held up. Not only that, a single stage metallic with no clear, you will not be able to buff out any flaws, and will have to live with as how shot, or repair scratches by wetsanding and buffing in the future. Even a solid is not guarenteed you will be able to cut and buff either, some colors (blues) could leave you with color rings.

There are some single stage urethanes that are pretty affordable today, and really not much more expensive then enamels. They should have better durability, so you may want to compare prices between the two.

By far the best and easiest way to go would probably be a base clear system, even though they are a bit more pricey. There is a reason they have taken over for the majority of auto paint jobs.
The base drys quickly, so repairs can be made to it if needed after a little set time. You still don't want to shoot too dry, as it may hurt the adhesion of the clearcoat, but you don't have to really worry so much about keeping a good gloss level in the base, just spraying the metallic evenly. Base drys fairly dull anyways, and the clear provides the gloss. Also a clearcoat provides more uv protection to the color, which is why you really don't see a lot of oxidation, color fading on cars today like years ago. The clearcoat usually gives up first. With a urethane clearcoat, required upkeep (waxing, garageing) should be minimal. Also you can buff dust nibs and flaws out of the clearcoat, and repairs of a base clear system in the future should be easier. Also shooting a two tone is easier, as you can tape off a two tone too paint the second color in a much shorter time, and clear the works and bury the line in clear. Sorry to try to spend your money for you, but a base/ clear really would be the best way for you to go.
I am not a chemist and haven't shot enough single stage and how long they last, but the life expectancy of a single stage generally isn't as long as if a clearcoat is used. I am sure some of the better singlestages with better pigments and uv protectors might last quite a while, but some colors like red that are known to fade, in a single stage could start dulling and oxidizing quickly, while others might last a good while (like my white bonneville). As far as I understand, two types of uv protectors can be used in a clearcoat, while a single stage can only use one. There is only a thin layer of resin that floats to the top to protect a single stage.

Just guessing, and depends somewhat on color, but would say an enamel ss life expectancy maybe a few years if driven daily (probably a little over a year in red), a ss urethane a bit longer, a cheaper line of base/clear maybe about 5 years, and a top line urethane base clear about 10 year plus.