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I am in the process of painting some plastic parts(fog light cover) on my Toyota Camry. I started with sanding the plastic to prepare it for the primer layer and while doing that, in some areas I reached the actual plastic below the original paint layer.

When I started applying the primer, at first it looked fine but very quickly I noticed that it started to lift in some areas. Initially I thought that it was simply too much primer but then I noticed that the lifting occurs exactly on the edges of the sanded areas. Below is a picture I took after sanding the initial lifted primer and applying some actual paint to see if that's gonna make any difference (it didn't).

enter image description here

Hopefully the image is clear enough and you can see how the paint has lifted exactly around the areas where the paint was completely sanded off and the actual plastic became exposed.

Any idea how that can be avoided/fixed?

Currently I am thinking of applying some spray putty to create an additional layer that hopefully won't lift so I can properly apply the primer and paint on top of it.

  • Is the primer suited for use with plastic? Was the part clean of dust from sanding? – CharlieRB Jan 31 '17 at 15:42
  • @CharlieRB Hi, I am not sure about the first question. I just explained the guy in the shop what I am about to do and her recommended me this one. I would assume it will. And yes, I washed the part with water and wiped it dry – Eugene S Jan 31 '17 at 15:47
  • Ah, it may not have been completely dry when you sprayed it. Surface moisture can cause this to happen too. Make sure the part is completely dry. Even though you wiped it dry, there can still be moisture there you can not see. – CharlieRB Jan 31 '17 at 15:50
  • @CharlieRB That wouldn't be the case here as it was completely dry. And, as I explained, it is clearly has something to do with the exposed plastic edge as these are the only areas this is happening. Thanks – Eugene S Jan 31 '17 at 15:52
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    I'm pretty sure you need a self etching primer on raw plastic in order for it to stick. You might want to check to ensure that's what you're using. – Pᴀᴜʟsᴛᴇʀ2 Jan 31 '17 at 21:35
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Dealerships are known to spray rubbers and plastic with some kind of silicon spray to make them appear new and clean. Silicon spray, even when it's been sprayed on something a year ago, makes that you can't paint something that it's been sprayed on. The paint will show all kinds of disturbances in your painted area. That might be your problem. It helps to clean the to be painted area thouroughly with a good cleaning agent. Naturally, the plain water you used won't suffice for that. I suppose there's stuff for sale that's specifically made for this kind of cleaning.

  • Hi and thank you for your answer. The thing is that the paint actually sets pretty good on the original paint but behaves like in the picture only in the areas where it was sanded, or to be more precise around them. – Eugene S Jan 31 '17 at 16:48
  • @EugeneS Your sanding has probably removed the spray with it, but it's still present on the unsanded area next to it. It'll still contaminate the adjacent area that you're painting. You'd have to clean the area with an extra margin of, say, 5cm/2inch. – Bart Jan 31 '17 at 16:52
  • Sorry maybe I read it wrong but it seems that what I am experiencing is exactly the opposite because my paint holds just fine in the areas where I did less sanding and the original surface is exposed. I have another plastic cover just like this one which I sanded very slightly with a very fine sanding paper and this one came up perfect. – Eugene S Jan 31 '17 at 16:56
  • @EugeneS Then it may be that your paint and the underlayer paint of your car are incompatible. It could be that they have a different base solvents that interfere. I have encountered that problem when wanted to respray old cars(from the 60s) with today's paints. In that case, you'd have to find a primer that is compatible with both. – Bart Jan 31 '17 at 17:01
  • This is a 2003 Toyota Camry. Could that be the case here? – Eugene S Jan 31 '17 at 21:13
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This is called lifting. Applying a proper primer prior to applying the new paint will Block the old paint and prevent it from lifting. Also, start by applying the new paint in light coats and allow it to dry completely before applying more Coats. This worked for me back when i was in the auto body business. Keep in mind the new paint has strong solvents in it and can react to old paint as paint stripper.

  • Thanks for your input! – Eugene S Jul 31 at 15:18
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What sort of primer did you use? You might find you need a specialist plastic primer to get it to adhere properly to the plastic.

I'd also try rubbing the plastic with a bit of coarse sandpaper to 'key' the surface, which should also help the paint to adhere to it - paint doesn't stick well to very smooth surfaces.

  • Hi and thanks for your input. I was using this primer here: supercheapauto.com.au/Product/SCA-Etch-Primer-400g/288525 – Eugene S Feb 2 '17 at 1:11
  • This is really interesting that you say surface must be coarsely sanded before painting as it contradicts with all the instructions I found online and in the shop. The general suggested technique was sanding with coarse to very fine sanding paper, then applying primer and only then paint. – Eugene S Feb 2 '17 at 1:14
  • Etch primer is for bare metal, I'd use something like this for plastic: supercheapauto.com.au/Product/… – Nick C Feb 2 '17 at 10:48

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