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painting resin and masking question

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when priming and lacquer painting an object , in this case the hood  of a car , i am having the masking lift the paint . How do you avoid this with a primed resin surface ?  

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I once had a resin kit that gave me paint adhesion problems. I tried everything available, and in the end it was good old Humbrol enamel that gave me the best adhesion. It had to cure fully, multiple days, but then it stuck. I used it as a primer, and then continued with other paint types.


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Cast resin will have tooling release agent on it, in addition to that, most but not all casting resins will have amines on the surface which will stop materials like paint from sticking to the surface (this is the waxy feeling you get when you wash off the release agent)

Best way to do it is to mechanically activate the surface.
I wouldnt tell you to sand it as to most people that implies sanding away at the surface to remove something.


I use a thumbnail sized piece of scotchbrite dipped in RO water, just give it a quick light rub over, that will remove what is on the surface without removing any of the resin.

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8 hours ago, Dog1 said:


what is RO water ? what you are saying is to to do the treatment from scratch before applying the primer ?

RO water is just really clean water... You could use distilled water I guess. Its just what I use because I have it.


You dont really want to scratch the resin you just want to remove what is on the surface of it.

Which is why I dont say to sand it as sanding it with a sanding stick for instance will remove some of the resin.


its like a pan scrubber but an industrial version of it (its also a little bit thicker with more air between the "fibres"). The harder you press the more abrasive it gets.

I guess you could use a pan scrubber and some tap water if you really wanted to. The one thing you are doing is trying not to remove any resin from the part, so dont sand it, otherwise you are trying to scratch the amines and release agent from the surface of the resin.

The very fine lines that you do put into the resin will activate the surface ("key up" the surface) so the paint finds it easier to stick.

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On 7/25/2021 at 12:06 PM, Dog1 said:

 just distilled water and scotch bright or add a little plates detergent ?    

Add a drop of dish washing liquid to your bowl of warm water, use an old toothbrush and scrub everything really well. Rinse off the parts and dry them. You can also use your airbrush to blow the water out of the nooks and crannies. Prime and paint.


Edited by A-10 LOADER
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I just use water, I dont put anything in it at all as the scotchbrite will abrade it enough.
If you want something softer then an old toothbrush and water with some kind of cleaner like fairy liquid will do (or other dish washing up liquid that is designed to attach the oil and grease to the lather), but as you seem to be having problems getting paint to stick (so I assume you have already tried the softer method) then I would go with some scotchbrite rubbed very gentle over it to activate the surface.


You will need a thicker than usual primer after that of course, Mr Surfacer will do. The thicker version of it will do just the job. Then a nice base over the primer before you spray your colour coat over the top.

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After having extensive adhesion issues with Reskit resin parts, I found that Mr. Metal Primer works very well with waxy resin parts.  If you are using the version from the bottle, thin it about 65% with Mr. Color Leveling thinner.


I've also had good luck with enamel primers, but I don't work with enamels that much anymore due to slow drying times.

Edited by sigtau
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