Primer-free 'Paint Keying' for Weathering Effects

[70021 Morning Star]

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HOW TO PROVIDE A PAINT 'KEY' WITHOUT USING PRIMER PAINT ?
 
If you've ever tried weathering a model without first applying a coat of Primer, then you're likely to find the paint simply rubs off, as there's no 'key' for the weathering paint to grip and hold onto. Even minimal handling will remove all of your weathering detail.
 
The traditional advice is to use a spray Primer before before applying the weathering paints, especially if you're airbrushing. But, in my experience, Primer paint tends to be quite thick. Not really something I want if I'm weathering something as small as an 'n' scale locomotive. It's even worse on an 'n' scale Steam Locomotive, as I only want to apply the 'keying' to areas I'm weathering, not the whole locomotive, and it's hard to mask off the factory-applied handrails etc., when using a spray Primer.
 
Just recently, I've found that a Methylated Spirits moistened cotton bud, seems to work quite well.  So far, I've only used Meths on Dapol locomotives. Methylated Spirits seems to remove a very small amount of the factory paint, leaving a dull flat finish, comparable to using T Cut, but much easier to apply. Just be careful to monitor how much paint you're removing: Don't use too much Meths, or it'll pool in areas you definitely don't want it ; use a good supply of cotton buds and watch how much paint is deposited on each cotton bud as you proceed. Remember, 'less is more', and use a dry cotton bud to wipe off the wet Meths as you do your 'keying' in small steps. 
 
The dull flat finish is exactly what is needed to provide a 'key' for the weathering paints. After which, a semi-gloss or semi-matt finish can be achieved using water-thinned Humbrol "Clear" gloss varnish. IMPORTANT: notice I said "water-thinned. If you don't thin, you will end up with a gloss finish, that seldom  looks good on an 'n' scale model. Also, Do NOT apply Clear until you've finished all of your weathering, as absolutely nothing - neither paint nor weathering powders - will adhere to Clear for long! That said, you mustn't get Clear on any weathering powders, or they'll change colour and you'll lose the intended effect.
 

UPDATE  - suggest replacing the cotton buds with a paintbrush. The cotton buds leave too many bits on the model, which are a pain to pock off. A paint brush will work just as well, without any risk of  leaving a mess.

 
I'd be interested to know if anyone else has a novel way to create a paint 'key' without using Primer?
 
 
Enjoy your modelling,
Rick

[70021 Morning Star]

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American nitro-acrylic paints

 

These contain Acetone, and so (in theory) the Acetone should attack the plastic, eating it away. However, if my understanding is correct, Kato USA Paint their models in this stuff, and model shops sell it for railway modellers to repaint their locomotives and rolling stock.

 

I'm thinking the Americans may like the nitro-acrylic as it 'self etches' itself into the plastic? If this is correct, it'd mean you don't need primer or any other way of creating a 'key' for the paint. That's interesting if you're starting from bare plastic, but you can't apply this stuff over British water-based acrylics, as the Acetone in the nitro-acrylic will act as a paint stripper on the water-based acrylics.

 

Does anyone have any experience of using American nitro-acrylic paints on Kato USA models, please? I have a Kato Union Pacific locomotive which I need to alter. I know I can airbrush the nitro-acrylic onto the Kato model - as the expert supplier says it'll be ok - or I could use a British water-based acrylic, but the colour match won't be so good.

 

Any help gratefully received.

 

Many thanks,

Rick 

[Mick Bonwick]

I've never had a problem with weathering rubbing off. I don't tend to handle my stock very much once it's weathered, nor before it's weathered either, come to that. Not sure how many people would handle stock a lot, unless it's to remove it and replace it when exhibiting. Even the edges of running plates on steam locomotives seem to resist the wearing away of paint to a certain extent, although I have seen acrylic paint coming off of coupling rods and other motion components. That's normally because the metal wasn't cleaned of oil properly before starting, though.