Why is my paint job dusty?

[Milo]

It’s kind of textured and when I rub my finger it comes off noticeably. 
Tamiya lacquer on Tamiya lacquer primer airbrushed

[Ace-Garageguy]

Sounds like "dry spray".

Possible causes: 1) Insufficient thinning; 2) air pressure too high; 3) shot from too far away; 4) paint passes too fast; 5) excessively hot air temp with very low humidity; 6) any or all of the above in combination

Edited June 14 by Ace-Garageguy
TYPO

[Milo]

I haven’t gotten the hang of thinning yet… could it be too thin or too thick?

Plus, I live in central texas and I work in the garage, it’s consistently mid 90 F

[Dave G.]

11 hours ago, Milo said:

I haven’t gotten the hang of thinning yet… could it be too thin or too thick?

Plus, I live in central texas and I work in the garage, it’s consistently mid 90 F

A good way to mix your paints is not so much by ratio, though I know everyone wants to hear about ratios . Rather, put some primer in a mixing cup. Add the thinner and mix, stir it with a mixing stick. Add a bit at a time till when you take the stick and wipe some of the mixed paint up the side of the cup, it returns back down the side of the cup in 2-3 or 4 seconds or so but leaves a film behind. If you find yourself waiting 10 seconds or more and wonder if it's going to ever get back down to the pool below, then obviously it's too thick. If it returns in a second but leaves no film as it returns, then it's too thin. Adjust accordingly.

Your paints in your Your climate would do well using a slower thinner in your paints. Try something like Mr Leveling thinner in your primer, it has a touch of retarder that aids initial flow out of the paint on the surface before flashing.. At one time actually Tamiya had a slower thinner as well, not sure they still do.

Try what I'm saying, let us know how it goes. In no time you will have a feel for this with lacquer primer. This is much easier to do than to explain or for that matter, to read.

[Milo]

I also have the problem of trying to be as bare minimum as possible, and most cost effect. I’ve been using those giant tubs of lacquer thinner you see at Walmart, and I’ve been avoiding all the expensive model brands when I can.

[TarheelRick]

The Wal-Mart/Lowes/Home Depot thinners work fairly well with most paints. To add to David's comments, when you remove the stir stick from the paint you can count the drops of paint and time them as the fall from the stir stick. Of course the quicker they fall the thinner the paint will be. I seem to remember reading somewhere you should get a drop a second, but don't quote me on that. Maybe someone else will chime in that has used this method.

[Claude Thibodeau]

Hi!

The Wall Mart generic lacquer thinner is VERY hot, meaning it might attack the styrene your model is made of. Further, it can de-bond the primer (and paint)  molecules so that they refuse to form a film, as they would with model thinner (such as Tamya's). To be certain, try your same routine and products with Tamya's lacquer thinner. 

I rencently ruined a test panel by thinning model acrylic paint (a British brand) with Tamya's ACRYLIC thinner. The hobby store paint dept guy told me Tamya's acrylic thinner contained alcool, which was too strong for this paint. I tested it with pure water, and it airbrushed flawlesly. 

Thinner matters! Good luck 

CT 

[Dave G.]

2 hours ago, TarheelRick said:

The Wal-Mart/Lowes/Home Depot thinners work fairly well with most paints. To add to David's comments, when you remove the stir stick from the paint you can count the drops of paint and time them as the fall from the stir stick. Of course the quicker they fall the thinner the paint will be. I seem to remember reading somewhere you should get a drop a second, but don't quote me on that. Maybe someone else will chime in that has used this method.

You reminded me of my days learning to refinish 1/1 cars and trucks. I was taught to thin the paint by use of a viscosity cup. A viscosity cup is basically a very precise small funnel shaped device. You dipped it into the mixed paint and in X amount of time it should have emptied out the metered stem.. Eventually you just know what the right flow rate is without the cup and just letting the paint run off your mixing stick. It's how I learned though, my products and viscosity cup being Dupont. This was supplied through the Dupont automotive paint dealer I used at the time. Those were fun and rewarding days !

[Skip]

22 hours ago, Dave G. said:

You reminded me of my days learning to refinish 1/1 cars and trucks. I was taught to thin the paint by use of a viscosity cup. A viscosity cup is basically a very precise small funnel shaped device. You dipped it into the mixed paint and in X amount of time it should have emptied out the metered stem.. Eventually you just know what the right flow rate is without the cup and just letting the paint run off your mixing stick. It's how I learned though, my products and viscosity cup being Dupont. This was supplied through the Dupont automotive paint dealer I used at the time. Those were fun and rewarding days !

If I remember right from inspecting paint for a really big used to be Seattle based Aircraft Manufacturer; the Cup you are talking about is called a Zahnn Cup.  Sets in a heavy wire rack with another catcher cup below it. Dump a measured amount of the thinned paint into the top cup then time how many seconds it took to empty the top cup. Next there is a formula for the Temperature and Humidity factors and that gives the Viscosity of the paint.  Didn't have to use this on most of the Commercial aircraft but had to do it on every Military variant.  The painters all used the stick, the inspectors were forced to use the Zahnn cup and compute the viscosity...

No one else has commented, but you said that your air temperature is around 90 deg F. that's pretty warm to be shooting paint, could be that you are having flash off occurring in the air before it hits the painted surface as dust. You might look into a high temperature reducer (thinner) to somewhat counteract this.  Humidity at 90 deg shouldn't be an issue, in Texas it's probably next to zero hot & dry! What about painting in the morning when the dewpoint is a little higher for at least a few percent humidity and the air temperature is lower to help you with the flashing issue. It's worth a try, and you might not even have to mess around with switching reducer. You also might be picking up some dust out of the air as well, if you can cover the painted model with a stainless-steel bowl, plastic bowl... to guard against the dust you might help that issue. Being that painting is a process you can check off one step at a time to isolate the source of the issue until it's found.

[Dave G.]

1 hour ago, Skip said:

If I remember right from inspecting paint for a really big used to be Seattle based Aircraft Manufacturer; the Cup you are talking about is called a Zahnn Cup.  Sets in a heavy wire rack with another catcher cup below it. Dump a measured amount of the thinned paint into the top cup then time how many seconds it took to empty the top cup. Next there is a formula for the Temperature and Humidity factors and that gives the Viscosity of the paint.  Didn't have to use this on most of the Commercial aircraft but had to do it on every Military variant.  The painters all used the stick, the inspectors were forced to use the Zahnn cup and compute the viscosity...

No one else has commented, but you said that your air temperature is around 90 deg F. that's pretty warm to be shooting paint, could be that you are having flash off occurring in the air before it hits the painted surface as dust. You might look into a high temperature reducer (thinner) to somewhat counteract this.  Humidity at 90 deg shouldn't be an issue, in Texas it's probably next to zero hot & dry! What about painting in the morning when the dewpoint is a little higher for at least a few percent humidity and the air temperature is lower to help you with the flashing issue. It's worth a try, and you might not even have to mess around with switching reducer. You also might be picking up some dust out of the air as well, if you can cover the painted model with a stainless-steel bowl, plastic bowl... to guard against the dust you might help that issue. Being that painting is a process you can check off one step at a time to isolate the source of the issue until it's found.

That system sounds a bit up scale from what we used, but same principle.

As to the 90f temps, I agree. But I'm not the OP trying to spray in that situation.

[Ace-Garageguy]

One old rule-of-thumb when I was painting dinosaurs with lacquer was "the right viscosity is about like skim milk". 

After a while it became second nature to thin paint products correctly, and I could even "hear" from the sound of drops leaving the stir stick hitting the paint in the cup, and tell if I needed more thinner.

Today, with most professional refinish products requiring quite accurate mixing using graduated containers, there's little to no guesstimation.

But the OP's problem is yet another reminder why we harp on TEST ON SOMETHING OTHER THAN A MODEL to figure out what you need to do to get a good finish with a specific product or equipment.

And believe me, though I've been painting real stuff, expensive stuff, for more than 5 decades, when I shoot anything on real cars today I sure as h. don't go in the booth and start blowing paint without first dialing in the gun for whatever material I'm using...on a scrap test panel.

EDIT: most excellent splellchuck has never heard of "scrap" and wants it to be scarp or scrape or scrip. It doesn't like "dialing" either. How do the people that program this garbage get jobs?

Edited June 15 by Ace-Garageguy

[Milo]

6 hours ago, Ace-Garageguy said:

One old rule-of-thumb when I was painting dinosaurs with lacquer was "the right viscosity is about like skim milk". 

After a while it became second nature to thin paint products correctly, and I could even "hear" from the sound of drops leaving the stir stick hitting the paint in the cup, and tell if I needed more thinner.

Today, with most professional refinish products requiring quite accurate mixing using graduated containers, there's little to no guesstimation.

But the OP's problem is yet another reminder why we harp on TEST ON SOMETHING OTHER THAN A MODEL to figure out what you need to do to get a good finish with a specific product or equipment.

And believe me, though I've been painting real stuff, expensive stuff, for more than 5 decades, when I shoot anything on real cars today I sure as h. don't go in the booth and start blowing paint without first dialing in the gun for whatever material I'm using...on a scrap test panel.

EDIT: most excellent splellchuck has never heard of "scrap" and wants it to be scarp or scrape or scrip. It doesn't like "dialing" either. How do the people that program this garbage get jobs?

everyone says skim milk, and nobody has ever even seen skim milk other than at the hotel breakfasts 

[JollySipper]

I believe that I would be trying to get decent results from spray cans first........ That may kinda lessen the learning curve of using the airbrush. Then you can see what a spray pattern should look like and how paints act once on the substrate (flow-out and flashing).

Something that may help is to remember what HVLP stands for with the real spray guns......... It's 'High Volume, Low Pressure' which is how the 1:1 paint guns work.

[Milo]

you underestimate me, which makes me sad. I’ve made many kits using spray cans, and until now have had good enough results from airbrush until summer. I was fine in the winter and even early spring. 

[Ace-Garageguy]

26 minutes ago, Milo said:

... until now have had good enough results from airbrush until summer. I was fine in the winter and even early spring. 

Well, that right there ought to tell you something, right?

Apparently the temps are high enough and the humidity low enough now that your paint is drying and literally turning to dust before it reaches the model.

[Dave G.]

7 hours ago, Milo said:

everyone says skim milk, and nobody has ever even seen skim milk other than at the hotel breakfasts 

Hah, low fat milk is close enough, heck even whole milk will get you there, heavy cream too much ! Now I'm the kind of nut who actually likes to experiment. Having constantly heard of the skim milk thing forever, I once took low fat milk and put some in a mixing cup. Swirled it around, son of a gun if it didn't leave a little film behind as I swirled it. Best of all I saw how is sloshed in the cup, got a feel for it's viscosity. Next ? You guessed it, I put it in an airbrush, it sprayed perfectly at just about any pressure setting. And just cleaned up with plain old water. With that test satisfied, I know what low fat milk looks like and behaves like. LOL. But you're right, I'm not sure in my 74 years on earth if I've ever encountered skim milk other than seeing the label on cartons of milk. I told you about the run back test on the side of the mixing cup. Viscosity cups, others drip tests off the mixing stick. I think you get it.

So, paint ratio or viscosity may not be your issue at all. You need to spray in the cooler hours of summer or slow that drying down. Unfortunately " cooler hours" can also bring in humidity in the form of dew point, the lacquer painters worst nightmare, warm temps high humidity. And now rather than the dry dusty surface, you get fogging or so called blushing.. My personal answer for airbrushing in your summer climate would be to use enamel products, which are less prone to these things. Course you could always move inside to where there is AC I assume, it's not like your painting a 1/1 1960 Cadillac or something ! I shoot my LP lacquers into a trash can inside. The smell isn't much and it's gone in ten minutes anyway. I do that in the winter because it's too cold out and in the summer because it's too warm and humid outside. Now enamels I get out of the house or use the booth. But even then I'm right back in with the fresh paint job and into the paint dryer/dehydrator.