Using filler primer?

[Ron H]

Howdy all, I've been stripping and epoxy priming my fifty seven a section at a time. I had intended to sand the epoxy primer and then apply color on top of that. However after reading in the classroom section, in the "finish body work and start priming" area, section five. It stated I should use a 2K or filler primer on top of the epoxy primer and then sand. I don't remember anyone previously recommended this to me. Have I been wasting my time and primer by sanding the epoxy? Is that what I need to be doing, or just continue sanding the epoxy primer and color over that? Is there an advantage of one over the other? I had planned on using a bc/cc finish on top. Thanks for the help. Clueless in Texas, Ron

[SamG]

Ron, unless your body is VERY straight, and/or your bodywork is VERY nice, most epoxy primers will not provide the level of fill that you need to do any serious blocking. Dont get me wrong, you can build epoxies (some of them anyway) and use them as filler primers, but they are generally much slower to dry than urethanes or polyesters and do not sand quite as well. That said...Pete, who used to visit the board quite frequently, used ONLY Kirker epoxy primer for all of his primer work. I have used quite a few gallons of Montana epoxy primer and found that if you let it sit long enough, it could be dry sanded with ease, but didn't have the filling power of a urethane.

You havent messed up anything. Read the p-sheet for your epoxy. You may be able to come back now and apply a 2K primer on top of your sanded epoxy using the tooth created by your sanding for a physical bond, or you may want to recoat for both a physical and chemical bond (if your p-sheets say so, some do).

--OR--

If your'e happy with what you've got, you're confident that your panels are straight and slick enough to satisfy you (that's what really matters anyway), move on to the sealer/paint phase

Keep us posted

SamG

[Len]

When we sand dry we use "dry guide coat" and when we wet sand we use aerosol guide coat. These products make it a lot easier to get the surface perfect because you can SEE the irregularities while you're sanding.

[Pot]

Ron, with a 57 model anything, the probability of needing a filler primer in addition to your epoxy primer is near 100%.

What is seldom explained on this or any other P&B forum is that there are different ways to arrive at the point of being ready to apply your BC/CC regardless of brand.

Generally speaking, epoxy primer is not intended to be a sandable, filler type primer. Different brands make a difference. Most people use epoxy primer in lieu of etch primer, then apply a urethane filler primer which is the one that is used for sanding/blocking prior to BC/CC application. However, there are some "aftermarket" brands that combine an etch primer with a filler primer. AutoBody Master brand comes to mind.

Each brand has it's "quirks", recommendations and advice. That can sometimes lead to confusion. For example: If you are exposed to PPG advise, you will hear all the stuff about epoxy primers. If you are exposed to DuPont, you will rarely hear about epoxies especially in the context of production work.

Especially for new guys, it's best to keep to complete systems. Pick your brand and stick with it. You have the rest of your life to experiment with some other combinations and mixing of brands.

In case it isn't already obvious, I belong to the crowd that uses only etch primer(when needed), urethane filler primer, polyester primer if needed, then BC/CC. I only use a sealer between the primer and the basecoat under unusual circumstances.

[Ron H]

Thanks, Sounds like I need to use the 2k or filler primer, do I just use this on the exterior panels as opposed to door jams trunk lip etc? Also, am I better off to do all the panels, hood trunk lid doors etc mounted on the car, or does it matter? Just seems like it might be easier. Or should I do each panel, piece as I get them primed with the epoxy? Do you recommend wet over dry sanding? Seems as though wet has been easier for what I have done. Less fowling of sand paper, less dust etc. As I've said I am totally inexperienced at all this and need all the help I can get. I never imagined this would be so involved a project and am clearly in over my head.

[Phil V]

Ron, epoxy primers main claim to fame is that it adheres really well to propery scuffed bare metal, it also has built in rust inhibitors. Materials sprayed on top of the epoxy primer also adheres really well to that epoxy primer.

On the other hand 2-K urethane filler primer has only one function in life and that is to provide a sandable film build up for block sanding to remove minor imperfections in the surface of a body panel. Say the panel has a couple minor low spots. By spraying 2-k high fill pirmer in reality you are filling in the low spots. But at the same time you are also adding to the higher surface around the low spots. So what you do is either spray on a "guide coat" of either cheap rattle can black lacquer primer in a very thin coat. Just enough black primer to make the surface of your gray 2-K fill primer look darker than the normal lighter gray. When that primer is dry then you get out your trusty long board hand sander with 150 - 180 grit paper and start block sanding the panel to make sure its flat. This is where the reason for guide coating comes in ---- as your sanding the panel you will quickly see what is flat and you will also quickly see where the low spots are. The areas that are high or flat quickly get the darker guidecoat primer sanded off and the lighter gray primer is showing. But if there is any low spots then the darker primer hasn't been sanded off because being a low spot the sand paper couldn't sand that area.
In a case like that what you do is keep block sanding the panel until either -- "A" - the low spot/darker primer disappears while sanding or "B" you sand through your 2-K high fill primer and hit bare metal around the outer edges of the low spot. As soon as you see bare metal --- Stop. Mix up some more primer and repeat spraying more primer on as well as more guidecoat rattle can black primer and when that is dry you repeat the block sanding procedure until the whole panel is flat with no low spots and no bare metal.
At that point you apply one or two more coats of 2-K high fill primer and when that primer is dry you wetsand it with 600 grit paper. When thats done you can either spray your color coat directly over that or I would suggest spraying a couple medium coats of epoxy primer over the whole car just prior to color coating/clear coating. No need to sand the epoxy sealer coat if you spray your color coat within the "re-coat window" (each epoxy primer is different, some brands are only 24 hours while other brands go up to a week to where you don't have to sand the epoxy primer in order to spray your color coat/clear coat).

I should add that Len sells two different kinds of guide coat materials specifically designed for that purpose. Its a safe bet that the guidcoat materials Len sells won't plug up your sandpaper like cheap rattle can lacquer primer will if you spray on a little more than you really needed. One of the guidecoat materials Len sells is a black powder that is put on with a special hand applicator. That would have some definate advantages.

If any of this stuff doesn't make sense or you're a little confused feel free to ask more quesitons. Thats why we all come here, to ask questions and to answer other questions, that way we all learn new and better ways of doing this type of work.