Hi and greetings from Greece.
I will try to pass you the situation I'm in...
I decide to paint my wife's car. I will use a 50lt - 2,5hl compressor & an LVLP gun (Sprayit SP-33000).
The problem is the previous paint that the car has. Let me explain:
Car bought used 6 years ago, with a cheap paint job on it (as it understand now).

Some panels have been dull over years. Tried to rub a small spot with acetone and it took off almost instantly (must be an oil based paint, right?).
Some panels are OK. Acetone rub does nothing to them.
One door have some spots with clear coat flaking. The basecoat on this spots took off almost instantly with acetone too (oil paint again? Is it possible to have a clear coat on it?)

As a newbie, I wanted to avoid priming the whole car and I want to prime only the spots needed. I also want to use a single stage paint - no clear coat, so I need advice on the process/products I should use.
I think that 2K Acrylic paint is a no go because of the old oil-based paint. Am I right?
The products I choose are from a Greek company named HB Body. Specifically at first I was thinking about using this 2K:
https://www.hbbody.com.gr/product/index.php?pid=105
but because of the old paint, I was thinking to use this (it is cheaper too but I am worried about durability and lasting):
https://www.hbbody.com.gr/product/index.php?pid=104

Thanks in advance for your time!!!

Whether you paint over the existing paint or refinish the first thing you should do is wash the car. Then go over it with a wax and grease remover frequently changing rags. Any foreign substance especially waxes or polishes need to be removed from the surface.

The "Cheap paint job", can you depend on it not to peal off? Painting a car is a lot of expence and work and if you paint over a bad paint job and it peals your paint will come off with it. It's your call but the only way to know your paint job will hold up is to take it down to the metal and start over.

I'm in the US and don't understand the specifications on your compressor. Amazon showed the sprayer but didn't show the tip size it comes with. You may have to practice spraying enamel paint with the sprayer before using the expensive automotive paint to get used to the sprayer. Your compressor if it doesn't put out enough air you may have to paint like the hood or a fender at a time so you don't run out of air.

If you are going to paint over the existing paint all you would have to do is sand the finish smooth with some 400 to 600 grit sandpaper. If you don't sand down to the metal anywhere there wouldn't be a need for primer.

If you went over the old paint with acetone and the finish dissolved then the finish was probably lacquer. If it wrinkled up like you put paint stripper on it then the finish was probably some type of enamel. A urethane would be more chemical resistant.

Your paint products are certainly different there. I think it would be best to ask them about the products and compatibility.

Thanks for the answer!!!

The compressor is 13 gallons 2.5HP rated at 6CFM/90psi
The gun is rated at 3.0-3.9cfm consumption/22psi and it has a 1.3 tip.

The paint is on the car ~7 years and I think that it is reliable not to peel off. You think it would be better to strip it down to metal;

So you think that I can paint directly with 2K acrylic over the 3 pieces that have lacquer or enamel?
Also, why at the spots that the clear peeled off, why I can put away the basecoat with acetone? Could it be lacquer or enamel under acrylic clear?

You are asking for trouble by trying to paint over a failing paint job.
If it wasn't failing you wouldn't be wanting to repaint it so the only correct way is to strip the old paint off.

If you insist on painting over the old, wash it as described earlier and then run over the surface with a DA using 80 grit. Use a Maroon Scotchbrite pad to dull the areas the DA can't reach.

Wipe the car clean with an Automotive Wax and Grease remover - NOT acetone or lacquer thinner as they will leave a film on the car.

Spray with a quality two part Epoxy. This will reveal any incompatible materials as the surface will wrinkle. If the Epoxy lays down well with no issues you can then spray a 2k (two part) build primer, follow block sanding procedures as outlined in the Sticky Posts at the top of this forum and then proceed to spray your color. (I would only use a 2k product for color and clear)

Again, we don't not advocate or recommend substandard painting procedures or materials.

mc92661 wrote:Thanks for the answer!!!

The compressor is 13 gallons 2.5HP rated at 6CFM/90psi
The gun is rated at 3.0-3.9cfm consumption/22psi and it has a 1.3 tip.

The paint is on the car ~7 years and I think that it is reliable not to peel off. You think it would be better to strip it down to metal;

So you think that I can paint directly with 2K acrylic over the 3 pieces that have lacquer or enamel?
Also, why at the spots that the clear peeled off, why I can put away the basecoat with acetone? Could it be lacquer or enamel under acrylic clear?

Your equipment should be sufficient to paint the car.

The 2k acrylic won't adhere very well to lacquer. If you are going to paint over lacquer better go over it with epoxy primer first. If you plan to keep the car for a decade or more it would be in your best interest to strip it down to bare metal and do it right. It's one of those things you have to make the call.

The clear needs a mechanical bond to adhere well. The reason it peals is because nobody sands the base coat before applying the clear. You just shoot the base on and when it's dry enough the clear is shot. It takes the scratches made by sandpaper to make a good bond. If you sanded the base chances are it would muddle up the appearance of it.