Proper paint prep

[fireguyfire]

I'm starting to prep my 73 challenger to be painted back to factory colour (brite red).
The car was repainted once a deeper red years ago, and the paint is still in decent shape.
I started blocking the repaint off with 180 grit and have gone down through the overpaint and it's primer to the original paint; once I've blocked that out I have a very level and smooth surface, although there is still quite a bit of original paint on the car.
I've heard 2 schools of thoughts over the years regarding repaints; 1) if the original paint has been sanded and prepped, leave it as it is a great base for a new paint job;  and 2) always take all of the old paint off to bare metal.

Looking for opinions on whether I should keep blocking down to the original paint and making it dead straight, or should I take all of the paint off to bare metal and start over.

[fireguyfire]

This is what I'm getting after blocking down past the overpaint; dead level and we'll adhered.

[Shane Kelley]

Take it all off. Those areas where you sanded through will show up in the new paint job after a little time sitting in the sun. You also need to know what may be hiding under the finish. Last thing you want is a bubble showing up in your new paint job when you find out somebody covered up a small rust hole. Paint and materials are to expensive to gamble with issues showing up later.

[1 Wild R/T]

Personally I strip every car, I don't want to chance a reaction between old material & new...  How long of a block are you using? I would try to use at least a 12" block & prefer 18-24... The longer your block the straighter the panels...

[fireguyfire]

I use a 24" block.

[Shane Kelley]

Your pic shows multiple layers of paint and I also see lacquer primer. You got to strip all that off if you want a quality paint job. There's no primer or sealer that's going to hold all that mess together.

[fireguyfire]

So, in that case my plan would be to sand it down to bare metal using 80 grit, skim the car with mud and then icing before prime, block and paint.
Does that sound right?

[tparker]

A lot of it has to do with your trust in somebody elses work. It is possible it will all be fine. BUT, there is a lot of time, money, and energy spent to find out there is a problem later down the road. I Personally would sand down to the original color from the factory as that should be a solid base. However, I'm no paint guy, but a lot of good painters say the original paint makes a solid base if it is in good shape. I only went to metal where I needed to do body work and rust was an issue.

[Rich G.]

Take it  down to bare metal, spray the whole car with an epoxy primer. Now you have the metal sealed and know exactly what you're working with. With the price of materials these days why take a chance.

[Shane Kelley]

You can sand it down like you mentioned. I usually chemical strip it with aircraft stripper first. Might take 2 or 3 applications to get most of it off. Then wash real good with a red scuff pad and Comet or Ajax. This is a important part of the process because it neutralizes the stripper. It might look clean wiping it with a solvent but it's not. Dry it off and finish sanding everything with 80 grit on a DA or use a Roloc disc to get everything else off.

[headejm]

@fireguyfire FYI - Shane Kelley is "da man" when it comes to body and paint issues. I'd definitely follow his recommendations. Come to think of it, he's also "da man" when it comes to mechanical issues and especially with Mopars. 

[fireguyfire]

I'm definitely going with his suggestions on paint removal!

[Cudajason]

I'm definitely going with his suggestions on paint removal!

Once you have it in Primer you can do any required body work...no need to skim the whole car in mud at any time.

one any required body work is done, prime and block!!!



Jason

[torredcuda]

I like to strip to metal for a couple reasons - don`t trust the condition of old paint or others work and also there may be surface rust or small pits in the metal you can`t see that will come back later. Media blast, sand or chemical strip all work. Two ways of doing primer /mud - some say epoxy prime first and do mud work over that, others do mud work first and then prime. I always mud first, epoxy prime then high build primer, block everything, prime again, final block.

[fireguyfire]

That's a sweet Cuda!
I'm used to working on much worse cars where I'm welding in new quarters, dog legs, etc etc so I have to give a skim of mud to ensure it's straight. This car is factory sheet metal in very good shape and appears to be very straight.
My plan will be to epoxy prime, then rough block that down to show me any body filer or hammer and dolly work; once I've done that, then 2 coats of high build blocked in between; then the single stage paint.
Does that sound logical?

While we are discussing this stuff with guys that know more about it than I do, what would be the suggested grits for blocking the epoxy and high build primers to ready it for the colour coats?