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Post by endevol on Nov 6, 2010 18:55:02 GMT
Evening All,
My first post, and unfortuantely, it's a dumb question that has doubtless been asked plenty of times before. I couldn't see any old threads on this so I guess I have to ask it again.
I need to prime a polystyrene kit. It's made in 2-colour styrene and I want to give it an all-over same-colour base coat. OK, I know I can buy enamel primer in a tinlet, but I'm going to need quite a bit and don't want to pay through the nose. So I googled it. There seems to be a body of opinion that says you can use cellulose primer from Halfrauds and spray enamel over that. But then some websites warn that cellulose won't key to polystyrene, and the resultant finish will be fragile.
Does anyone have any personal experience or reccomendations on this subject? What primer do you use?
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ptcruiser
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Car & Motorcycle SIG Leader
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Post by ptcruiser on Nov 7, 2010 10:27:58 GMT
Hi Endevol You need to use Halfords Plastic Primer, comes in white, grey and I think red oxide. I believe it's acrylic based, as are all of their top coats.
This will serve as a primer for whatever paint type you wish to put over the top.
Using cellulose paints direct onto plastic is going to cause you a problem as after a while it cracks and flakes off. It doesn't bind to the plastic, hence the use of the plastic primer.
Hope that helps? Rich
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Post by endevol on Nov 7, 2010 17:24:58 GMT
Thanks for the info - that ties in with some of the advice I'd already been given. I didn't realise you could spray enamels over acrylics, though. You learn something new every day, as they say.
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ptcruiser
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Car & Motorcycle SIG Leader
Posts: 1,223
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Post by ptcruiser on Nov 7, 2010 21:28:09 GMT
It's more difficult the other way round - acrylic over enamel. Enamel is regarded as being"hotter" than acrylic. This I think (not being a qualified chemist) is down to the solvents in use. Enamel has a higher oil based content as opposed to acrylic which is either water or a "lighter" chemical solvent such as isopropyl alcohol. Cellulose is "hotter" still. You can probably get away with acrylic over "hotter" base coats if you leave a lot of time for the base coats to "gas out", or in other words give the carrying solvent time to totally evaporate from the application. Thus the vapour is not trapped under the acrylic layer and can not react with it.
Probably an over simplified and not 100% accurate rendition, but one I can understand at least. Rich
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Post by NoelSmith on Feb 4, 2013 18:06:33 GMT
In the art world using acrylic paint over oils is a No! No! Enamel is Oil Based paint so same principal applies. Enamel is OK over Acrylic or Cellulose but not the other way around.
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