Airbrushed surface rough

Hi All,

Need help, what to do wrong? I am beginner in scale modell with airbrush, then painted with airbrush after dry, the surface very rough.

Thanks!

Tibor

Hi Tibor,

there are a number of reasons this might happen.

What kind of paint did you use? If you used something like Tamiya you might be able to airbrush the surface again with lacquer thinner and get it to smooth out some. But regardless knowing what kind of paint you used might help get responses that will help you move in the right direction.

Regards,
Phil

It sounds as if the paint dries partially before it hits the surface.
Which brand/type of paint are you using?
What do you dilute it with?

Too much air or too high pressure. Spraying to far away from the surface.
Some paints need a retarder to slow down the drying process.
Thinner that evaporates too fast.

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Hi Phil,

Thanks your answer. As usualy use mr color and revell. Unfortunately always happend this. If i am mixed lighter or harder the paint, same surface.

Tibor

Without more details about your particular issue, I can only go by the general causes of that sort of problem.

The solution is probably that you need to decrease your air pressure, increase your paint flow, and get closer to the surface. However, all of these factors work in combination, so it’s also possible that only one of them is the actual problem or that a change in any one of them will resolve your problem without needed to change the others.

What you need to achieve is applying the paint so that it is still slightly wet on the surface without any runs, drips or pools. You also need to avoid creating over-spray by blowing the aerosolized paint around corners, edges, and into concave areas. You want to apply the paint in overlapping passes mating a wet edge to a new wet edge. The paint needs a moment to “self level” on the surface, and it cannot do that if it is already almost dry while still in the air.

Self leveling is when the wet paint has just enough time to spread out on the surface and create a smooth surface on the paint layer before it “flashes off.” The droplets of still wet paint must flow together to form a continuous layer of wet paint before “flashing off.”

“Flashing off” is the point when the paint dries (or cures) to the point where it is no longer a liquid and cannot run or flow on the surface. (It may still be soft and easily scratched or dented or marred by finger prints, though.)

“Orange peel” or bumpy surfaces are caused by one or more of the “holy trinity” of air brush factors being out of balance with the others. These are paint viscosity (how much the paint is thinned), paint flow matched to air pressure, and distance and surface speed.

So, you can spray thicker paint if the paint flow and air pressure are high, but if you do, you need to also adjust the distance and surface speed (of application) to allow the paint to self level on the surface.

If the air pressure is too high but the paint viscosity is too low and the paint volume is also too low, then the aerosolized paint droplets will “flash off” while still in the air and land on the surface as partially dried “balls” of paint rather than as “droplets” of liquid. The “balls” then create a rough, pebbly surface rather than “self leveling” into a smooth finish.

Also, if the air pressure is too high and paint flow / volume is too low, the surface immediately under the air brush may be painting fine, but excess aerosolized paint droplets are being blow around corners and into spaces where, by the time they land, they have “flashed off” and dried into “balls” vice landing as wet "droplets. Again, the result is a rough, pebbly surface on these other areas.

The viscosity of the paint may be fine and it lays down and self levels directly under the airbrush, but it’s too low to retain enough thinner / carrier in the aerosolized droplets to not flash off while still floating around in the air as “over spray.”

So, long explanation, but the solution is almost always the same: Without changing your paint viscosity or volume (paint flow), you should reduce the air pressure and move closer to the surface.

If this gives you too little coverage for a given pass (i.e. the area being painted is too small), then you need to increase distance, paint flow (volume) and slightly increase air pressure to delivery a wet spot of paint to the surface.

If the paint wants to drip, run, or pool because you have increased the volume, then you need to increase the surface speed, decrease the viscosity, or increase the distance (and air pressure).

The bottom line is that air brushing is a balancing act of many different variables. each variable prioritizes one aspect of the application (area covered, speed, or drying time) and the other variables must be brought into balance with that particular priority.

Most modelers find a “happy medium” or compromise that they are comfortable working within and then stick to those variable conditions. That is they almost always thin their paint the same way, use the same air pressure, and use the same paint flow and volume. Once they are content with a paint viscosity, they tend to stick with that, then, and will usually only change their air pressure and flow when they want to move closer and spray a tighter line (air pressure down flow down), or move further away to spray a wider line (air pressure up flow up).

So, what you need to do is a bit of experimenting and testing to find a workable balance between paint viscosity, air pressure, paint flow (volume), distance and surface speed. You want to shoot for a best “average” to give you good, controllable coverage with a smooth surface, no runs, drips, pools or orange pool. Probably best to start with paint viscosity (for your brand and thinner / reducer of choice).

Once you have a good, workable average with that viscosity, then you can experiment with changing air pressure, paint flow, distance and application speed that to see where your total range of application is.

When you notice undesirable outcomes, you can trouble shoot by changing one of the variables to prioritize what you’re trying to achieve and bringing the others into balance with that one changed variable. Over time, you’ll develop enough experience to predict what will happen and then confidently change any of the variables to achieve any particular desired outcome.

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Hi SdAufKla,

Thanks for your very expert ansver. Can you explain what is perfect ratio of the paint mixing? I can imagine not easy to explain this.

Thanks!

Tibor

As with the other variables, there is no hard and fast answer to this question. There are many reasons why this is so, but the fact that actually measuring the viscosity of such small quantities of paint is not only difficult, but also uneconomical. So, if I’m going to mix up several liters of paint for an automotive painting project, measuring the viscosity is quite easy and almost all of the paint is recovered back into the mixing container.

However, I will leave more paint in the viscosity measuring cup clinging to the sides than I will use in most of my airbrushing projects. In fact, my viscosity measuring cups require more paint than most full bottles of hobby paint contain before opening. Thus, as a practical matter, it is not possible to precisely measure the viscosity of a hobby paint for an air brushing job.

What we are then left with are many and diverse opinions based on comparative observations and anecdotes (i.e. stories). I know this doesn’t answer your question, but it is important to know so that you can put the answers you will get into perspective. Basically, all that I can really do is to try to describe to you what works for me based on my own experience with the paints and thinners that I use along with my own air brush and air pressures. The answers you get may sound very exact and precise, but in the end, they are really individual observations and descriptions. With this in mind, here goes my answer. (There are sure to be others, too.)

I air brush almost exclusively with Tamiya cellulose based acrylics. I generally thin (reduce is the more correct term) my paints around 60:40 to 70:30, paint to reducer. This is quite a range, but the starting viscosity of the paint in the jar can also vary quite a lot from one jar to another (unless you’re using brand new, unopened jars). Basically, the older a jar of paint is, the more likely that some of its carrier (thinner) has evaporated before you go to use it. This “thicker” paint needs more reducer than the same paint new, in the jar.

Also, the exact painting job may require getting the air brush quite close (for example thin lines). This close up work demands lower air pressures (to avoid over spray) and to keep the paint flow (volume) small to avoid runs, drips and puddles in very small areas. Lower air pressure then demands thinner (lower viscosity) paint. Lower viscosity paint has less opacity (that is, it has less pigment per given volume so it doesn’t cover as well). This also means that tight lines need to be sprayed closer to concentrate the paint in a smaller spot which circle back to lower flow (volume) and closer working distance.

The opposite goal requires the opposite approach. Wider spray patterns intended to cover larger areas should be done with higher viscosity paint, which demands higher air pressures, greater paint flow (volume) and greater working distance. Higher viscosity paint is not reduced (thinned) as much.

Finally note that the air brush tip and needle size will limit the maximum viscosity that you can actually spray out of that piece of equipment. Smaller tips and needles generally give better results spraying lower viscosity (thinner) paints. Heavier, thicker paints (higher viscosity) require larger tip and needle sizes to spray well. Here we must match the potential paint volume (flow) with the paint viscosity. Lower viscosity paints can be sprayed at low volumes with low air pressures. Higher viscosity paints must be sprayed at higher volumes with higher air pressures.

For this last reason, many model builders have different airbrushes with different tips and needle sizes or they may have different sized tips and needles that can be switched out for different painting jobs. You need to know the specifications of your own air brush tip and needle to know the general working parameters for it.

Generally, a way to judge the viscosity of the paint is to compare it to water or alcohol (very thin / very low viscosity), skim - low fat milk (a good medium viscosity for most uses) or perhaps whole milk (a medium-high viscosity for greater coverage and area).

I mix most colors and thin them right in the paint cup on my airbrush. I measure the paint and thinner by drops using a pipette or medicine dropper. I always add the thinner first (allowing one extra drop of thinner to fill the tip of the air brush) followed by the paint. I will use the pipette or medicine dropper to agitate and mix the paint by drawing it in, back and forth.

I will run a few drops down the inside of the air brush paint cup to judge the viscosity (alcohol, water, skim milk, whole milk?). This is where there is no substitute for experience, so you must develop some habit to always judge the viscosity of your paint every time you mix it. (The above is just my method.) Over time, you will learn what works for the job you’re intending.

FWIW, it doesn’t really matter what type of paint you’re using. All that matters is reducing it to the proper viscosity. So, when I sprayed hobby enamels, like Humbrol, Pactra, Revell, etc., I thinned my paints to the same viscosity. I still occasionally spray a hobby lacquer (Floquil Model RR Colors). These are also thinned to the same viscosity as I thin my Tamiya paints.

So, again, my thinning ratios range from about 60:40 to 70:30, paint to thinner. I suggest starting with these and then assessing and judging whether you need your paint thinner or thicker based on observed spraying performance.

There are other issues that can have an impact on best thinning ratios (the porosity of the surface, using inks vs. actual paints, ambient air temperature and humidity, etc.).

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Hi Tibor,

what thinner do you use, as both of these do not like the same thinner. Is it something that easily evaporates?
The best thinning advice is to thin outside of the airbrush, in a clear plastic pot. You can find small disposable ones in the supermarket. Then add paint first and then thinner. Mix well with stirring stick or toothpick. Now you are going for a skim milk consistency (I hate that term) so when you move the paint to the wall of the cup it will flow down easily and leave a very transparent thin film on the walls. you can play around with the opacity but remember more layers are better than one thick one.

Second tip is to go with a very thin layer for the first one, almost dust. This is a good surface for the next layer to attach to. Then when doing subsequent layers position the light in such a way that you can see if the color goes down wet or dry. Ideally you want wet that dries within a couple of seconds (light reflection tells you the state). then do more layers over this. You should get a nice smooth layer.