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Old 08-20-2012, 09:19 PM   #1
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Base color coat sticking better then primer?


I have a small spot of rust on a door panel on my car and after sanding down to bare metal, cleaning the area and letting it dry, I've been trying a couple different primers. Ive tried an enamel primer, an all-purpose primer, and a self etching primer, and all 3 seem to scrape off very easily using my fingernail after drying for 4-10 hours. They dont just peel right off but it doesnt take much effort with my fingernail. I've read that epoxy primer is highly recommended but I would think between the 3 I had I should be able to get one of them to stick. I decided to try something different and just skip the primer and see how well the base color coat sticks to the metal. After prepping the surface again and applying some of the base color coat to the bare metal, it seems to be sticking very very well after only maybe 30 minutes of drying. So I would think that something more needs to be done to prep the surface for paint, but the fact that the base color coat is sticking alot better then the primers has me wondering. The base color coat that Im using comes from a rattle can that contains a special order "Enamel Blend" color that my car came with from the manufacturer.

Can you see any reason why the primers I was using werent sticking too well but the base color coat was?

Maybe I'm just not waiting long enough for the primers to fully dry before testing their hold?

Any problem with skipping primer all together and just applying 3-4 coats of base color coat and clear coat? (its on the bottom edge of the door panel so its not necessary for the job to come out perfect)


Last edited by konsole; 08-20-2012 at 09:25 PM.
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Old 08-20-2012, 10:19 PM   #2
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Base color coat sticking better then primer?


Remember the primer is not necessarily supposed to provide much protection from being scratched off, with say your fingernail. Its job is to adhere chemically to the material being painted and to provide an even and consistent surface to which the paint, and ultimately your clear coats can bond. It is them that provide the protection from scratching.

You don't want to skip the primer because depending on the type it may have other properties like rust inhibition. I would continue with the self-etching metal primer. Ordinarily you would only use one coat but you may have to make several passes if you are using rattle cans.

It also sounds like you may be rushing the primer's drying time but I don't have the can in front of me nor do I know how humid it has been where you are.

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Old 08-21-2012, 04:19 AM   #3
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Base color coat sticking better then primer?


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Originally Posted by sdsester View Post
Remember the primer is not necessarily supposed to provide much protection from being scratched off, with say your fingernail. Its job is to adhere chemically to the material being painted and to provide an even and consistent surface to which the paint, and ultimately your clear coats can bond. It is them that provide the protection from scratching.

You don't want to skip the primer because depending on the type it may have other properties like rust inhibition. I would continue with the self-etching metal primer. Ordinarily you would only use one coat but you may have to make several passes if you are using rattle cans.

It also sounds like you may be rushing the primer's drying time but I don't have the can in front of me nor do I know how humid it has been where you are.

along with everything else you said
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Old 08-21-2012, 10:41 AM   #4
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Base color coat sticking better then primer?


Shouldnt the primers have sufficiently dried enough after 4-10 hours that they dont peel off so easily?

I know thats not enough time for them to fully dry and harden but sufficient adhesion to the surface should have happened by then I would think.

The base color coat that I've had on the bare metal since my last post has stuck to the metal very well by now.

If primer is really just paint designed to join the surface and the base color coat then whats the harm in skipping the primer if the base color coat is sticking so well?

Last edited by konsole; 08-21-2012 at 10:45 AM.
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Old 08-21-2012, 04:23 PM   #5
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Base color coat sticking better then primer?


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Shouldnt the primers have sufficiently dried enough after 4-10 hours that they dont peel off so easily?

I know thats not enough time for them to fully dry and harden but sufficient adhesion to the surface should have happened by then I would think.

The base color coat that I've had on the bare metal since my last post has stuck to the metal very well by now.

If primer is really just paint designed to join the surface and the base color coat then whats the harm in skipping the primer if the base color coat is sticking so well?
probably crappy primer or improper prep before application
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Old 08-21-2012, 04:45 PM   #6
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Base color coat sticking better then primer?


..maybe a car shop would have paint for...cars!
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Old 08-21-2012, 08:27 PM   #7
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Base color coat sticking better then primer?


I think I've determined that the oil based primers from spray cans arent having an issue sticking to the surface. The 1 water based primer I have is the one having the issue not sticking too well and scraping completely off very easily. So the oil based primers are sticking well to the metal but I've found that after about 6 hours drying, the solvents in the oil based color coat just dissolve the primers. I assume I could just apply the oil based primers and let them fully cure for like a week before I start on the color coats, but I've been driving around without the door panel on and I'd prefer not to wait a week or more to get the panel back on. The area I'm painting is small and not normally visible so it wouldnt me much of an issue using a different color paint then my car that is water based and wont dissolve the primer underneath. However, I want to use the color paint I have because it matches the cars color perfectly, and I'd prefer not to buy a water based paint in this color even if it does exist, because this custom paint is very expensive.

So the oil based primer sticks well to the metal but the solvents in the color coat dissolves the oil based primer.

Is my only option to wait for the oil based primer to fully cure for atleast several days and then apply the color coat that contains the solvents, or would the solvents dissolve even fully cured oil based primer?

I'm having a hard time seeing how an oil based paint with solvents could ever be used effectively on an oil based primer without the primer dissolving.

Last edited by konsole; 08-21-2012 at 08:29 PM.
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Old 08-21-2012, 08:47 PM   #8
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Base color coat sticking better then primer?


There is apparently quite a few things about paint you have to learn.
One is , paints for houses works best on- wait for it....

Houses!

And car paints and primers work best on, Ok you guessed it-

And there are reasons for that.

it has to do with the substrate,the kind of wear and the kind of finish.
All things to do a little research on .
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Old 08-22-2012, 06:12 AM   #9
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Base color coat sticking better then primer?


OP, You are going to drive yourself crazy trying to get products inherently not compatible with each other to work together. If your finish coat is reacting chemically with your primer you are not following directions for the type of primer to use under the finish.

I am not sure what you want from us at this point?

Stop mixing and matching with no regard for the materials you are trying to use. Use a primer appropriate for your prepped substrate and that is compatible with your finish coat material. Use clear coats compatible with the paint finish. Trying to invent a rounder wheel here is going to get you nowhere and at some expense.

You could also take the door to a body shop and let the folks do their thing. You seem to be spending an equal or more fortune than it would cost on products that are not working.

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