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Ok so i decided to prime my SM ( plastic - all been washed with warm water and cleaned ) with skull white ( doing white scare paint theme ) using an AB , i mixed the paint so it was milk consistancy , when i started to airbrush the paint wasnt sticking well when i look at it closely it looked like mini spots all over the model , why is that? ive AB other plastics and it has a smooth layer of paint.

Could it possibly be that the paint texture was to thin?

It's probably too thin. Have you tried priming black instead? It would work a lot better for doing white. Prime, then do a layer of Astronomican Grey, then drybrush Fortress Grey, then drybrush Skull White. It takes much longer, but it eliminates having to do all that pesky blacklining.

Ok a few things will cause spotting.
if its too thin and you apply the coat too thickly. The thinner you make the paint the thinner coat you have to put on and let it dry before doing another. And admittedly some paints don't bind well once they are past a certain thinness. However again the solution is usually a very faint coat of paint in many layers letting each dry.

There is another caveat to the above statement. What you thin it with. I often use windex because thinning with water can cause water dropleting if the surface isnt prepared properly or the paint is too thin with water. the windex often evaporates faster not giving the paint time for surface tension to pull away causing blotchy spots. so with water you cant thin quite as much I believe(I stopped using water a long time ago because it was causing me problems) Dont inhale too much of the ammonia though. Also some paints dont like windex, or dont thin as well with water or whatever. this will also lead to uniformity problems.

Another possibility is bad paint. Ive had some paint that was partially cured in the bottle which I thought I rejuvenated but it was doing all kinds of horrid stuff when I tried to spray it. old paints should be thrown away when they are suspect, put out to pasture for ork projects, or filtered carefully.

Yet another is poor atomization(read cheap brush or bad paint prep) Poor atomization will cause "globules" or less consistent spray. the surface tension of the larger globules will sometimes lead to spotting near them if the surface isn't hydrophylic(and it rarely is).

Now yet *another* possibility is prep.
1. I usually sand tanks to make darned sure the primer and paint stick. 600 grit or higher and barely touch it.
2. soap and water or isopropyl are good. I use IPA because sometimes if you leave a bit of soap on the model that will interact badly with the paint. IPA is water and alcohol and evaporates. Just be sure when using IPA to use a good wash cloth or paper towel to actually remove the oils. then don't touch it. your oils, even a small amount will act hydrophobic repelling the the water based paint especially when you put too thick a layer on in one spray.
3. As Cheese elemental mentioned primer is very important. I usually sand, clean, prime and often clean again with IPA, very lightly once the primer has dried.

Hope that helps.

what atropos907 said...

Using plain water to thin will give mixed results. Some paints work fine with plain water, others not so much. Not really such a thing as "too thin" as airbrush Candy colors are more or less just washes that are sprayed through an airbrush to tint existing colors.

I actually use a reducer made up of Windex, IPA, water and a little bit of Glycerin. It makes the acrylics I shoot behave like Urethanes (Urethanes are alot nicer to shoot through an AB than acrylics and dry alot faster but are hazardous and a lot harder to clean up).

Also, don't spray at too low PSI. The thinner the paint the less pressure you need but I would personally not drop below 20psi. The paint has to atomize before hitting the surface and the lower the pressure the "wetter" it'll hit the surface you are painting, hence the "blotchy" look. Give it around 30 seconds to start to tack, then do another layer. Using IPA or Windex will speed up drying time as those evaporate a lot faster than water.

Since you are using normal acrylic paints use a nylon stocking to strain the paint a little bit. Normal brush acrylics use a lot larger pigments than airbrush paints and can cause problems with how the paint goes on through an AB as very large pigments won't atomize properly.

I'd suggest going to a craft store, getting some cheap water colors, find some cardboard boxes to break up to use as canvas and just spend a few hours or days practicing. It may seem easy to do something as mundane as base coating a tank with an AB but it actually does take some practice and modicum of skill to pull off. If AB was as easy as using a rattle can (and those can be tricky too, I've seen enough patch jobs on cars to suspect the owner let a monkey do it) than anyone picking up an airbrush would be making $100+ dollars an hour (and yes, pros do charge that much on average) and turning out pro results the first time.

It will frustrate the hell out of you, it will try your patience and make you want to give up but stick with it. It's a technique similiar to learning how to use the old hair and stick brush. You didn't expect to turn out GD winning results first time you picked up a brush, don't expect to be doing car and motorcycles tomorrow and you will find you will enjoy it a lot.

thanks for the reply guys ,
i was using GW paint and used water as thinner , spraying at 20psi . maybe i might have used to much water to thin and will try thinning using windex

I use a 50/50 mix of water(distilled) and rubbing alcohol(99%) to thin acrylics. Works like a charm. Using good quality paint as a starting point is also a good idea.