Re: Question about body work / paint prep...

[Matt Haas <mhaas@xxxxxxx>]

John,

Short question, long answer. How bad is the surface rust? Is it really 
light or is there deep pitting? If it's light surface rust, do the following:

- Wash the car with a good grease cutting dish soap and towel dry.
- Degrease the area you're working on with a wax and tar remover.
- Sand with 60 or 80 grit to get most of the rust off. Make sure you sand 
back a few inches from the visible rust to make sure you get it all and 
that you dust the area off frequently so you can see what you're doing.
- Treat with a rust converter such as Navel Jelly (this is a mild acid -- 
make sure you follow the directions). Make sure that the rust converter can 
be painted over with the type of primer you're using.
- Wash with detergent, dry quickly, and degrease again.

If you have deep pitting, do the same thing as above but have the rust 
media blasted instead of sanding. If the surface rust is on a bolt on part, 
you can also have it dipped to remove the rust. Once the part's been media 
blasted, you may find holes that need to be fixed.

As far as primer goes, it depends upon what you're wanting out of the paint 
job. There are three different types of paint commonly used: lacquer (not 
allowed in California), enamel (this is what AMC started using in the 
mid-sixties), and urethane. There are compatibility issues between these 
types of paints but if you're planning on having the car stripped before 
it's painted (BTW, this isn't needed as long as the base paint is sound), 
you'll do okay with the spray bomb's you can pick up at an auto parts 
store. In the case of my American, much of the original paint is in bad 
shape and I'm planning on stripping the car before it's repainted so I'm 
going the spray bomb route for now.

If you're not going to strip the car, you really need to talk to the body 
shop that'll be painting the car and ask them what to use for fillers, 
primers, and paints (more on that in a minute). The reason for this is that 
if you apply a particular type of paint and there's an incompatibility 
between it and what the body shop uses, you've just lost your paint 
warranty. It may turn out that you'll need to buy a spray gun to prime it 
like the body shop wants. If you have a 5hp compressor, you can pick up a 
cheap spray gun at places like Harbor Freight that will work okay. Also, 
you need to know something about that base metal you're priming. Some of 
the body panels (such as the rocker panels) are galvanized. You need to use 
a primer that will stick to galvanized metal if you work in one of those 
areas. You can usually spot galvanized metal by it's speckled appearance 
when it's bare. Make sure to bring this up to the body shop as well.

Before you spray the primer, prep the surface according to the direction on 
the can the primer came in.

Once it's primed, you can then apply your filler (follow the direction on 
the can for surface prep). That filler may either be a light filler (such 
as a primer/surfacer) or you may need to use a medium filler (what's 
commonly called Bondo but use the EverCoat brand with fiberglass in it -- 
it's much better than Bondo brand, is water proof, and there's a good 
chance your body shop will be using it anyway) followed by a primer 
surfacer. This layer of primer must be the same brand as the first and must 
be listed as being compatible with the base primer.

Once you're done with the filler, apply a sealer primer according to it's 
directions. Same rules apply as before: same brand and listed as 
compatible. Generally speaking, you don't sand the sealer beyond what's 
needed for the color coat so make sure all you're happy with the repair 
before applying it.

Once it's primed, you really need to apply a color coat unless it will be 
sitting in a dry climate for two weeks or less. Primer, in case you didn't 
know, will absorb water over time which will cause rust to form under your 
new paint. Use a paint that's compatible with your primer and follow the 
directions on the can it comes in for surface prep.

As far as tools and supplies go, use quality sanding products and change 
when they quit cutting. I've had very good luck with Norton and 3M 
products. 3M tends to be a little more expensive than Norton but the 3M 
stuff seems to last longer. I also like using the 3M Velcro backed or Rolok 
sanding disks that you can mount in a drill for stripping paint. The 4 inch 
disks work good for large areas and the 2 inchers work good for tight areas 
(like door jambs). You'll go through them pretty quick so you may want to 
buy them a box at a time if you're doing a lot of stripping. These pads are 
also sold in different grits. There are both stripping disks and surface 
prep disks. You want the stripping disks.

You'll also need to feather the existing paint to bare metal with 80 or 100 
grit paper (you should end up exposing some of each layer of primer and 
paint and you shouldn't be able to feel the transition from paint to bare 
metal). You can do this with a rubber block by hand but a D/A (dual action) 
sander speeds the process up. I'm pretty sure D/A sanders are all air 
powered and are usually air hogs. A good one will draw much less air than a 
cheap one. I picked up an Ingersoll Rand model this spring that was $10 
more than the cheapies made by Campbell Housefield (and sold under many 
brand names) but uses half the air which means that my 5hp compressor can 
almost keep up with it under continuous duty. D/A sanders are also great 
for leveling medium fillers quickly.

Depending upon what you have to do for filler, you may also want a 16 inch 
sanding board. These are sometimes called body files and there are also air 
powered versions (which, btw, are pretty expensive -- decent ones start 
around $200 and you'll need a big compressor to keep up with it).

Grits of sand paper really depend upon the instructions for surface prep on 
the primer, filler, and paint you're using. My best advice is to follow the 
manufacturers recommendations.

You will want to get dust masks for sanding and depending upon the primer 
and paint you use, you may need a respirator. Check the directions on the 
cans for recommendations.

One final trick for prepping the car is to spray a guide coat on it once 
it's primed but before it's sealed. Use a contrasting color to the primer 
(make sure it's compatible!) and spray a light mist coat over the body 
panel, let dry, and take your long board with 200 grit paper and sand until 
it's gone. If you have spots that still have the guide coat in them, you'll 
need to add filler. If you go to bare metal in places, you have high spots 
that need to be lowered. Once you can sand the panel and remove all of the 
guide coat without showing bare metal, you have a perfectly smooth panel 
that will look awesome once it's painted.

Finally, you'll be doing a lot of sanding. Make sure that you buy lots of 
sanding supplies and only work in small areas so you have good places to 
stop when your arms get tired.

Matt

At 05:28 PM 11/8/2004 -0500, you wrote:
> What tools/methods do most of you guys use to prep body work for 
> painting?  I have several areas of surface rust that need taking care of, 
> since it will be a few months before I take the car in for paint work I'd 
> like to do as much of it myself as possible.  The rust spots will need to 
> be sanded out, and some sort of primer applied to prevent rust from 
> returning before I can get it to the paint shop.  Any particular tools I 
> should use, what grit level of sandpaper, and recommendations for primer?
>
> Thanks,
> John Livingston
> http://1965rambler.blogspot.com
>
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mhaas@xxxxxxx
Cincinnati, OH
http://www.mattsoldcars.com
1966 Rambler Rebel
1968 Rambler American sedan
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