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Have any of you tried to sand a model very lightly with fine sandpaper before priming to make the paint stick better?
Either metal or plastic models?

I recently had some paint flake of the rim of a plastic base and I figured its because its so smooth. So why not sand it lightly? And maybe even other big smooth areas on the model?

Anybody of you who does this? Or have any experience and can tell if makes any big difference?

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Edges of bases? Shouldn't really matter if they're smooth.

What I'd suggest is that your models are probably oily, even greasy fingers leave oils behind. Some models, particularly resin, sometimes need the oils removed from the casting process.

I'd suggest giving the parts / models a quick bath in warm soapy water if you have this problem. And wash your hands before handling the bare plastic.

Then rinse thoroughly in warm/hot water, and then dry the parts off. Easier while the parts are either on sprue or pre-assembled, anyhow.

Primer is made to stick to clean surfaces. Maybe the paint you used wasn't a primer, or maybe a low quality one?

That's likely the cause of the problem. Bases, for example, are probably the part you touch and transfer oils to the most pre-priming.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10037278.page http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10037278.page GMT
Scrubbing with a very fine abrasive: Yes. I use toothpaste to clean any mould release and/or any oxide coating (Most metals will form an oxide coating when exposed to air, it's chemistry. It also stops paint adhering properly) off them before painting. Silver/brass polish can also work.

Not to give them any shine, but to remove the shine and add some "tooth" for the paint.
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My first couple models were like that. Turned out to be oils from fingers. I usually handle them with my bare hands when removing from sprue and cleaning mould lines. When ready to paint I wash the parts and from that point on I wear nitrile gloves to handle the models all the way up till I a seal them with an acrylic sealant. Never occurred since. ]]> http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10037602.page http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10037602.page GMT Steel wool is finer then sandpaper, more flexible then sandpaper and has soap in it so use that.
but still, use it very, very gently or you will scrub away plastic details.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10037782.page http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10037782.page GMT http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10037864.page http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10037864.page GMT
That said, I do use 1200 grid sand paper with regard too mould lines and other cosmetics.In addition, I find that a brass wire brush is more useful than a toothbrush when stripping models of old paint. I also use it to scratch up parts that I suspect of being too smooth - mostly this is resin.]]> http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10039252.page http://www.dakkadakka.com/dakkaforum/posts/preList/759342/10039252.page GMT