Acrylics - is a primer needed???

As I have found with my products, all plastics are not the same. Some plastics have a waxy feel and they tend to repel most acrylic paints like rain drops on a freshly waxed surface. For these surfaces I like to prime.

Priming can be as simple as a quick overspray...much like applying hairspray...just to hold everything in place. This method of priming gives the paint something to latch on to.

A prime coat that covers the model for uniformity of color is another method. I use this to blend various surface colors (plastic, fillers and aftermarket bits) into one solid color or when I am applying a translucent color such as white or yellow.

Cleaning and wiping down your parts before applying acrylics is crucial for good adhesion. It may appear to stick during the beginning of the painting but it might begin to peel later during any masking operations. 

When it doubt, prime it out!

 

I always prime, usually with an acrylic—usually Tamiya flat light gray. I don't do this for adhesion, I do it to find surface flaws, or to back up translucent colors (in which case I use white or silver).

Frankly, those who insist that a lacquer or enamel primer is necessary under acrylics just don't want to take the time to properly clean the surface that is to receive the paint. However, as Bill (Grigg) mentioned, some plastics are nearly impossible to clean properly, usually because of a manufacturing problem with the plastic or the molding process which causes them to exude tiny amounts of plasticizer or unpolymerized resin for long periods of time.

Variouis brands of acrylic are thinned with different thinners. Thin Tamiya and Gunze with their proprietary thinners or 90%+ isopropyl alcohol. If the latter, any artists acrylic retarder will work. You need only a tiny amount of retarder, and add it to the alcohol, then add that mix to the paint. Polly Scale can be thinned with deionized or distilled water. The article in a recent FSM is a good guideline for thinners, or you can ask here if you want to know what alternatives can be used for a particular brand.

If a paint says it is "water thinned" or water-reducible, never use tap water. When in doubt, use the proprietary thinner for reduction, and Windex (with ammonia) or Simple Green for cleaning.

Acrylics are not a black art. The are different from enamels and lacquers to which many older modelers are accustomed. Enamels and lacquers contain solvents that readily dissolve mold release agents, plasticizers, finger oil, and similar surface contaminants. Acrylics generally do not. Get the surface clean and you should have little difficulty with adhesion. However, some brands have better adhesion than others (Tamiya, Gunze, Polly Scale all have excellent adhesion).

Ah, to prime or not to prime, that IS the question!

As stated previously, a properly cleaned and prepared surface shouldn't need to be primed. I have often not primed and have had wonderful success. However, in one particularily horrible case I painted a car body three times before throwing in the towel and using a primer. The paint literally fell off the surface. Once the primer was on, the rest was easy. Since then I prime everytime and haven't had any issues whatsoever. As some one stated, it also shows up errors in sanding and flaws in the surface (darn it!). I use Tamiya AS-12 Aircraft Silver for aircraft, and their Fine Surface Primer for everything else.

Acrylics are no longer a Black Art, and are very easy to clean up, and remove when you do make a mistake. I find them much more forgiving than enamels. My wife complains less, as well, which makes for a happier home!

Funny story, I called Testors a few years ago to ask about my problem with their acrylic tape peeling off when I masked.  I like their paint, but was having adhesion problems, obviously.   The guy at Testor (and they're very nice to talk to, in my experience) was very helpful.   He couldn't understand why I was having a problem.  He said he never had that problem.  I asked him EXACTLY what he did.  He said, 'well, first I put on my laquer primer....'. 

I've had outstanding luck with the tamiya rattle-can primers.  That stuff goes on beautifully and provides a great surface for acrylics to 'bite' to.   Try it, you'll like it!   

 

 

Kirk's spot on.

I always use acrylics, and I always prime, but that is because it makes the identification of flaws easier rather than because acrylics don't adhere properly.

The only issues I have ever had with acrylics are related to the slow drying time on some of the gloss examples.

Karl

It's not a black art.   When I got back into modeling a couple of years ago I went straight to acrylics because what I read indicated they are less volatile and clean up would be easier.

Before you paint make sure you have a clean surface (Cleanup with rubbing alcohol or something like Polly-S Plastic prep).  I prime but not every one does.  I found it is helpful because it helps spot flaws - seems, scratches etc.

Fine Scale had a great article recently comparing different acrylics, I would check it out.  I prefer Tamiya, Gunze (Hard to get now), Polly S.

I have never had issues with acrylics that I have heard people complain about so I would take the advice of the person at your LHS with a grain of salt.  My impression is this something that people whom have never tried acrylics tend to repeat.