Ok I have been reading here for the past 10 months that people are shooting at about 25 to 30 psi (at least that is what I thought I was reading). Looking back through a thread I have seen people talking about 5 to 15 psi?! Seriously?!

Ok, so I have a compressor, with a moisture trap, and a pressure regulator. I have two paasche airbrushes, and an Iwata clone. I shoot MOSTLY tamiya acrylics thinned with Denatured Iso. So what psi SHOULD I be shooting at so that I can avoid grainy finish? Thank you in advance and sorry for being stupid. Cheers.

Damon,
I routinely airbrush Tamiya at about 14 psi and Vallejo about 14-16 in normal situations and little less for fine work (about 12 psi). Properly reduced, both should spread like butter at those pressures.

Kirchoff

Also depends on if your brush is gravity fed or suction fed. I use a gravity fed Iwata HP-CS and usually set my regulator to around 15 PSI when using either thinned Tamiya acrylics or Vallejo Model Air.

However, most of my subjects currently are smaller (1/48 armor) and so I use my little Badger 100 with the side feed gravity cup (easier to clean too) and was having issues with the paints being grainy until I bumped my pressure up to around 20 PSI.

I use an Iwata compressor with moisture trap and regulator for either brush. Just my observations, but maybe that will help.

So, please correct me if I am misunderstanding, but I should be shooting below 20psi, yes? What consistency should my paint be then? I am looking more for a concrete example than a ratio, as I don't measure anything, even in my kitchen. Thank you guys for the feedback. Cheers,

I just re-read your post. I don't think it has much to do with your pressure as it does what you're using to thin Tamiya acrylics. Alcohol is an inherent drying agent. You might want to add a drop of an acrylic retarder to your current mix. Sounds like the grainy finish is due to the paint drying before it gets to the surface of the model. I always run a drop or two of the retarder in each cup when I spray Tamiya through my brushes.

Again, just my thoughts from having the same grainy finishes before with Tamiya paints.

Well, Damon, you say you want concrete examples, but you also say you never measure anything - I'm not sure how that works. If you don't measure, then you can't keep your thinning ratios consistant, and without some consistancy, you can't come up with something that's gonna work for you every time. A hit or miss approach seems kind of, well... hit or miss (with an emphasis on miss).

But, FWIW, here's a "concrete" description of what I do:

I mix hardware store laquer thinner and Tamiya X-20A at 1:1 ratio, then use that to thin the Tamiya paints 1:1. The laquer thinner makes for a very smooth paint flow and coats and helps keeps the air brush tip from clogging.

This works through both my Richpen Phoenix 213c (top / gravity feed) and Badger 200 (bottom suction feed). Both are internal mix, the first is double action, the second is single action. I use the Richpen for fine detailed work and the Badger for general work since it's easier to clean.

Air pressure depends on the amount of paint flow I'm using, the lower the paint flow (smaller, finer lines) the lower the air pressure and vice versa. I sometimes go down to around 5 psi for some detail work, but usually spray around 10 t0 20 psi adjusting the pressure for what I want to do. Sometimes, to get the really fine lines, I have to thin the paint a bit more than described below.

However, with thinner paint, either the air pressure has to be increased to ensure complete atomization or the paint flow needs to be reduced so that not as much paint needs to be atomized (or some combination of both). If you don't do this, then the lower air pressure is not enough to atomize the paint and you'll get spitting. Also, fine lines need to be sprayed with the brush closer to the surface than wider area spraying.

So, a typical set up for me is about 10 drops of X-20A direct into the paint cup, followed by 10 drops of laquer thinner. I use the eye dropper to mix this up a bit by drawing it in and out of the dropper. I then add 20 drops of Tamiya paint.

(This might be a mix of different colors adding up to a total of 20 drops and not just 20 drops of a single color. I jot these mixes down for future reference. Some I save if I really like them, others are just to be sure that if I need more paint, I can mix the next batch the same.)

I then clean the eye dropper in a glass jar of tap water with some glass cleaner added to it (call that mix about 9:1 - water : glass cleaner, but really it's just a small pint jar of water with a splash of glass cleaner added).

I use the CLEAN eye dropper to mix the paint and thinner already in the air brush paint cup. I do this by drawing the paint in and out of the eye dropper until it's all mixed up. A quick trip back to the water - glass cleaner to rinse out the eye dropper, and I'm ready to spray.

After I spray, I use the eye dropper to suck out any left over thinned paint, and depending on if it's a custom color or more or less the same color from the jar, I transfer the left over thinned paint right back to the Tamiya paint jar. I suppose a "purist" might frown on this, but I don't find the minute amounts of "foreign" colors are enough to alter the color and the little bit of extra thinner just makes up for what I lose to evaporation as the paint jars are opened and closed. If I do think the custom color will potentiall alter the base Tamiya color, I just dispose of the excess from the air brush.

Not saying this is the only way, or even the best way, but it is a method that works for me, and I do a lot of air brushing. In particular, the laquer thinner added to the X-20A really does help to smooth out the Tamiya paints and prevent the dreaded "orange peel" effect. Some guys use just the laquer thinner without any X-20A.

Air pressure, paint flow (volumn) and paint viscosity all need to be balanced (ambient humidity and temperature also play a part by changing how fast or slow the paint dries after leaving the air brush, both while it's atomized in the air and once it's on the painted surface) to get your air brush to work the way you want in any given situation. Change one factor, and the other two need to be changed as well.

This is why you can have a dozen dfferent people here give you a dozen different explanations on the air pressure or paint thinning ratios that that they use, and every one of them can be just as right as each of the others.

Not sure if this was "concrete" enough, but really, you'll have to start somewhere and adjust to get the results you want. Once you hit the "sweet spot," where ever that is for you, then you'll be able to replicate the resuts from project to project.

If you find that what worked during your last painting session is not working right now, the likely reason is that the ambient temperature or humidity are different (requiring anchange in the thinning - reducing ratios with your paint.) And so it goes...

HTH,

That was very useful, although a lot to absorb when not at my "desk". As for concrete things like 10 drops is great 9:1, not so much. When I say I don't measure I really mean that. To mix colours, I pour in some and then something else and when it looks right, viola! Replication is easy because I know what I want it to look like. Same when I cook, I do not measure as I know what I want it to taste like and I adjust accordingly. Things like ambient temperature and humidity can affect paint, just like it can effect cooking and food. What I need to know is HOW it affects things. If I know how all the parts work together then I can make a good judgement call on what needs to be added or adjusted to make it "taste" better.
all of your items above are great and will be added to the notes prior to my next paint session. If someone out there can give me a "concrete" explanation of how those three items can affect the spray that would help greatly. I.E. higher humidity will make the paint dry less quickly (this is an example I have no idea if this is correct). May be we can even start a new page under Painting for airbrushing like Ssgt Toms did for weathering. Could save a lot of guys a lot of frustration and wasted money. Thank you all for your feedback it is greatly appreciated. Cheers.

High humidity can destroy your work if water gets a chance to hit your paint job, and is a problem those in the Southern USA sometimes have to fight.

Darren what kind of humidity are we talking? 50% or like 140%? It rains here, but I am in the garage mostly and the spray booth has a blower, so what kind of conditions are needed to create issues? Cheers,

1. Humidity:

Higher humidity means slower drying times. Lower humidity means faster drying times.

If the humidity is very high, when the compressed air in your air compressor is released by the trigger of the air brush, the moisture in the compressed air can condense and form water droplets in the air tank (causing rust) and the air hose causing water drops in the sprayed paint and on the painted surface. The defense against this is a moisture trap.

Edit: Just noticed your question about how much himidity is enough to cause this problem - There is no set percentage. It just depends on the temperature and how high the air pressure is (i.e how high the compressor is presurizing the air) and how much pressurized air is being released at a given time. (The higher the air pressure, the more water the air can hold as a gas which will then condense as the pressure is released.)

If a compressor mounted water trap isn't doing the job, combine it with an in-line moisture trap as close to the air brush as is comfortable to work with. This is because the compressed air in the hose can also hold moisture until the air brush trigger is pressed. This causes the water to condense in the hose by-passing the tank mounted water trap.

2. Temperature:

Higher temps mean faster drying times. Lower temps mean slower drying times.

Humidity and temperature always co-exist in various combinations and how much or how little of each can exacerbate or mitigate the effects of the other.

3. Air pressure:

Is needed to atomize the paint (and draw the paint in bottom feed airbrushes).

Higher air pressure makes "finer" droplets of paint, but also blow those same droplets around more and this can "hold" the atomized paint in the air long enough to dry before landing on the painted surface and create "orange peel" and over spray.

Lower air pressure is needed to make finer lines because it doesn't blow the paint around as vigorously as higher pressures. However, the lower pressure cannot atomize the paint as efficiently as higher pressures. Therefore, the volumn of paint must be reduced or the excess paint will "spatter."

4. Paint flow:

Is the volumn of paint being feed into the air brush (by the trigger on a double action brush or the needle adjusting nut on a single action brush). More volumn requires more air pressure to atomize the paint and less volumn requires less air to atomize. (And note that technically, we're equating air pressure with air volumn, but those are actually two different variables, too. They're just generally close enough to consider as a single variable for this discussion.)

5. Paint viscosity (how "thin" the paint is):

Contributes to how easily the paint will flow through the brush as a liquid and how "fine" it will atomize once it is pulled (actually sucked off the tip by lthe lower air pressure caused by the moving air) by the moving air off the paint tip.

The higher the viscosity (the "thicker" the paint) the harder it is to atomize. The lower the viscosity, the easier it is to atomize. Remember from above, the air pressure being used also determines how the paint will atomize. So, higher or lower air pressure can be used to increase or decrease atomization in response to the viscosity of the paint.

Finally, higher viscosity paint generally "sets" or dries faster than lower viscosity paint since it has less carrier (thinner) in any given volumn than lower viscosity paint. Remember again from above the effects of humidity, temperature and air pressure on how fast or slow the paint dries, too.

One more issue with paint viscosity is how well the paint will "cover." That is, will the paint coat have enough pigment to do its job. Lower viscosity paint generally has less ability to cover (since there is generally less pigment per any given volumn) than higher viscosity paint. So, what might cover with a single coat of higher viscosity paint might require multiple coats with a lower viscosity paint.

(We won't get into how various paint brands and types - enamels, laquers, acrylics - or the composition of paint - pigments, binders, and carriers - contribute to the variables above, but they do.)

Now, there are many ways to internalize these variables (temperature, humidity, air pressure, paint volumn, and paint viscosity). However, here is one way:

Think about the perfect air brushed paint finish as a value that equals 1 (one). Now, each of the varialbles is a fraction. What we want to do is add each of the fractions (variables) so that the sum totals exactly 1 (one), not 9/10's or 1-1/10, exactly 1 (one). Within certain tolerances, we can divide the total of 1 (one) any way we want between each of the variables, so that in the end, we've "balanced" the effects of each when added to the effect of all the others so that we achieve the perfect finish value of exactly 1 (one).

So, in the end, you can see that as we adjust each of the variables, we cause the other variables to react to our changed conditions, too. The precise amounts of how each variable acts in any particular painting situation is, I suppose, a number approaching infinity. (So, back to how a dozen different people can achieve the satifactory results using different combinations of the variables and still get 1 (onoe).) However, if you understand how these variables work together, you can diagnose your airbrushing problems and change one or more variables to compensate or correct that problem.

I find it best to be more than just a little deliberate in mixing my paint (drops to drops is the same as ratios, BTW), especially, since that establishes a "constant" and leaves me only having to deal with air pressure and paint volumn to achieve my desired painting goals. Then if that won't work, I know that the solution must lie with an adjustment in paint viscosity. Adjusting air pressure and paint flow are also more flexible (fine lines, fat lines, large areas, tight corners, etc) when it comes to actually painting your subject than keeping those constant and always adjusting paint viscosity.

As an old 11 Charlie, I know that "doubble-bubble-trouble" comes from trying to juggle too many variables at once, so the above is about as simple as I can make it for myself and still hit the target after only the minimum number of adjustment rounds.

Though, if "salt to taste" works for you, I guess you should "go with what you know."

HTH,

Mike;
THAT makes sense. Thank you. Really there has never been a "formal" training period for me on the airbrush since I got my first one, it was just trial and error and only recently did I upgrade to the better compressor.
Having read through all that I think the issue was simply I am not thinning my paint enough. What I thought was thin, for hand brushing, is probably WAY too thick for the airbrush. Thank you again. That is why I love these forums. Cheers.

D'nada, Damon.

No formal airbrush training here, either, just a lot of OJT and more than a few "un-sat" paint jobs! I still vividly remember being dismayed at the "spider webbed" blotches on the side of my Monogram US halftrack when I used my first air brush the first time!

Back to your original question: "Grainy finish" or "orange peel" is caused by the paint drying in the air and not arriving wet enough to spread / flow on the painted surface. This can be corrected with either a change is paint viscosity (thinner paint) or a change in air pressure (lower it) or changes in both.

You might find that you have the pressure too high because the paint flow is too high. That is, you were getting spatters (too much paint and not enough air) and you adjusted your air pressure to get rid of the spatters, but now have "orange peel" (and maybe "over spray" problems too). The requires lowering both air pressure and paint volumn. Paint viscosity might then have to be adjusted as a consequnce of lowering the air pressure.

Anyways, hope this helps.

Hang in there. I've been using an airbrush to paint models since about 1973, and I still have to stop and puzzle out problems. Just comes with the territory.

I will work on it this weekend and report back. Thanks again. It really is nice to have a resource of people that have had the same experiences. Cheers.

All I know is that when I first sprayed Tamiya with its own thinner using a Paasche airbrush at 25psi and without using enough thinner to thin the paint I got that annoying grainy texture some complain about. Back then I didn't have a regulator and so I couldn't drop the pressure. After changing a few things (including getting a couple of new top-fed Iwatas, a new compressor, and regulator) I was finally able to spray Tamiya the way I always wanted to, smooth as butter. I spray at 12 psi with an Iwata Revolution CR and HP-CH and now I can get down to spraying hair lines with them. The grainy issue experienced by some is definitely due to high air pressure and not enough thinning.

Rob

Thanks Rob. Good to know that is more operator error than my airbrush being jacked up. Cheers.

Mike, I read your painting procedures, not once but twice, as I'm in the acrylic camp, as odor is a major issue in my house, and I mean major ! I've gotten great results thinning both Tamiya and Model Master Acrylics with straight Lacquer Thinner, but the smell (even with my home made paint booth), still cause some serious domestic issues. So I started using Tamiya X20-A.

X20-A is nothing more then Isoprobyl Alcohol diluted with distilled water at a 50/50 ratio, with some acrylic retarder, and a flow agent. Both are easily available at most art supply stores. Since I have three 250 ml bottles still unopened, I continue to use it, but once the supply is gone, I'm making my own. Way cheaper, and I don't have to stock pile the stuff out of fear of another Tamiya world wide shortage (of which they're becoming famous for).

I dilute the Tamiya acrylic paint (which is not a true acrylic in that isn't a water based product), 3 parts X20-A to 1 part of paint. Model Master paint (which is a water based acrylic paint) is diluted 2 parts thinner to 1 part paint, as I find it's thinner straight out of the bottle. It also has a much finer pigment size then Tamiya paints do.

Both paints are air brushed through a Paasche H-1 @ 18-20 psi. Humidity is a constant in my home as it has central air conditioning (best investment we ever made). Winter humidity low levels are a problem, and we do use a humidifier to ad some moisture to the very dry winter air from time to time.

As I further thin out paint to do camo work, I decrease psi some, but never go below 15 psi as I continue to cut back on the amount of paint.

Given the option of a great commercial paint booth that would eliminate all odors to the great out doors, I would revert to diluting all acrylic paints with Lacquer Thinner. It two best qualities, is that it doesn't evaporate nearly as fast as Iso alcohol, and it does seem to reduce the pigment size, making for a much smoother finish. Then again, if odor wasn't an issue, I just might revert back to enamels. Drying time was never an issue with me, as I left everything dry a min of 24 hours anyway.