How important it is to use a primer?

congratulations!

You are on of the (few) who can brush paint Tamiya acrylic.

I have not been able to do so, ever, even bought & learnt to use an airbrush, err last Century, to spray yellow!

Broadly speaking, for spraying:

Tamiya doesn't need primer, I often use it AS primer, (except yellow).

Other acrylics, expecially (IMO) Vallejo and Hataka DO need priming.

You will now get at least a dozen differing opinions.

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It's not needed all the time,enamels cover and adhere well,as do lacquers,I also mix my Tamiya with LT and it adheres well,but with some of the newer acrylics,for sure to get better adhesion and strength,and if you use different materials like resin parts or metal PE.it helps adhesion.

Priming also covers some imperfections and identifies others that need sanding and seams that need repairing.

When I do prime,I like Tamiya in the spray can fits my needs.

I prime everything using decanted Tamiya Grey Primer.  It takes all of the guesswork out of painting.  Also, like Tojo said, primer makes all of the imperfections show themselves so you can decide on how visible something will ultimately be and whether or not its worth fixing before paint goes on.  Primer can also fill fine sanding scratches that would otherwise show up with just paint on top of them.  I like decanting and airbrushing it, as opposed to going straight out of the rattle can.  It gives you a lot more control over where it goes and how much so you don't accidentally fill delicate details like rivets and panel lines.

Not only that, I found it is just about the exact color I need for my Langley.  I am using it for my finish color, except for small glitches that need brushing, and Testors light ghost grey matches the primer very very closely.

OP in this case I think the color orange is a part of the problem. Anything with yellow in it just doesn't sweem to have the coverage other colors do.

Bill

Eaglecash867

I prime everything using decanted Tamiya Grey Primer.  It takes all of the guesswork out of painting.  Also, like Tojo said, primer makes all of the imperfections show themselves so you can decide on how visible something will ultimately be and whether or not its worth fixing before paint goes on.  Primer can also fill fine sanding scratches that would otherwise show up with just paint on top of them.  I like decanting and airbrushing it, as opposed to going straight out of the rattle can.  It gives you a lot more control over where it goes and how much so you don't accidentally fill delicate details like rivets and panel lines.

 

JohnnyK

I agree with what you are saying regarding the importance of using a primer. However, I use the primer straight out of the rattle can. I find that the paint  that sprays from a Tamiya can is a fine mist. Nothing like the fire hose that comes out of a Testors' can.

That's the way I used to do it, but then I tried decanting and airbrushing it and found that even the fine spray from the Tamiya can is a massive fire hose by comparison.  Combine that with no longer having to wait for a wind/rain/snow-free day without the temps being too low or too high to take my work outside so I can use a spray can in Colorado?  I've never looked back.  I just finished extremely delicate repairs to a panel line where I slipped with the scribing tool, and I have a fully painted, decaled, and weathered surface going up to nicely-detailed rear cockpit, less than 1/4" away.  I was able to fill (with CA) the damage, sand, and re-prime the repaired area without even having to mask anything by doing it this way.   

Needing to use primer depends upon two things mainly: the type and color of paints being used, and the surface to be painted. 
Certain paints, especially acrylics such as Vallejo require a primer due to their weak adhesion properties. The primer gives them something to hold onto on the surface. And as you discovered with the orange, some colors such as white, yellow, orange, etc. are best applied over a light colored primer for a better end result.

Certain surfaces, such as resin and photo etch metals, are so smooth, that most hobby pants will not adhere well to them, and the paint gets scratched off or worn off by minimal touching or handling. A good primer over these materials goes a long way in improving the paint's hardiness in the aspect of resisting scratching or wear.

Jon_a_its

...You are on of the (few) who can brush paint Tamiya acrylic.

I have not been able to do so, ever, even bought & learnt to use an airbrush, err last Century, to spray yellow!

Broadly speaking, for spraying:

Tamiya doesn't need primer, I often use it AS primer, (except yellow)...

As far as brushing Tamiya paints goes, have you tried thinning them? I'm talking specifically about the acrylics.  I learned that they must be thinned, and then they can be applied with a brush. I figured this out airbrushing them, when I realized they need to be thinned for airbrushing.

I find I get my best results thinning them for brush painting when I use Tamiya's proprietary acrylic thinner.

For airbrushing them, I use the proprietary thinner, too, though lacquer thinner works for that purpose, too.

As far as Tamiya paints not needing primer goes, I think that again, it depends on the paint.  Do you mean their acrylics, or their lacquers?  Or their rattle-can colors, which are lacquers?  As others have mentioned, most recently stikpusher, priming helps the paint adhere to the surface.  And the type of paint and the type of plastic and surface matter a great deal. 

I find that Tamiya acrylics work best on styrene, resin, or white metal, when I lay down a primer coat first.  With their lacquers, the solvent is hot enough that it can bond pretty well without a primer. 

I still prime, though, not just to promote adhesion, but for other reasons mentioned in this thread, especially that priming can help reveal issues that still need fixing, before I should apply color coats.

Bet regards,

Brad