Do I need to sand old clear coat to apply primer for new paint?

Question

So I did a terrible job trying to match the paint on the doors (the doors had the old paint peeling off) with the rest of the car and I would like to repaint the entire car to have the same color. Wet sanding would be an extra lengthy dirty process so I was wondering if I can just apply new primer over the old paint which has already some layers of clear coat. Will the primer stick to the clear coat or will it peel off after a while?

I mean, in theory it makes sense to sand it as it increases the contact surface through its roughness, but I’m not sure that I understood correctly if the primer works like that or it just sticks on the surface it is applied on through some chemical bonding or whatnot. Can anyone help me with this? Thank you!

Pᴀᴜʟsᴛᴇʀ2 · Answer

I'm not a body man, however, I do know one thing about it: you get out of the pain what you put into it. The largest part of any paint job is the preparation ... I mean, like 80% preparation and 20% painting. If you do a crap job of preparation, you'll get a crap paint job out of it. If you're not willing to put in the time to do the job right, pay someone to do it for you.

Secondly, you're thinking is wrong about paint being a chemical bond. Primer doesn't work that way. There's a mechanical bond between the paint and the painted surfaces. In order to get paint to stick, there needs to be an amount of texture there so the paint and/or primer can have something to hold on to. If the surface is completely smooth, it will just peel right off. Even with subsequent coats of paint, you cannot let the previous coat dry too much, or the next layer won't stick to it. There has to be someway for the next coat to adhere to the previous coat. Without it the paint won't stick correclty and you'll get a crap paint job.

Do I need to sand old clear coat to apply primer for new paint?

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