I thin my Tamiya acrylic paints with Tamiya lacquer thinner and I usually get a good smooth finish.. but every now and then I get the dreaded grainy finish.. I spray at about 1 Bar, which I think is about 12 psi.. is this the right pressure, or should I go with a higher pressure when I use lacquer thinner? If anyone uses Tamiya lacquer thinner with their acrylic paints, what have you found to be the optimal pressure setting for that?

Hisham

I have spraying that combo somewhere between 15-20 psi with good results

Hisham - 1 bar is 14.7 psi

I should have added that I would not bet my life on the accuracy of the pressure gauge on an AB compressor. I would also expect different atomization at at the same pressure depending on the type of AB used (or strictly, the details of the shape of the nozzle). Comparing pressures with other modelers is certainty useful, but you don't have to get your pressure to match theirs exactly, its a starting point.

You really need to just experiment

Thanks for your replies.. I realize that ultimately I would have to experiment, but I was just wondering whether this combination works better with lower or higher pressures in general.

Thank you
Hisham

Hisham,
The pressure you are spraying with is suitable for well thinned (1 part paint 2 parts thinner) Tamiya paint if you are using Tamiya or Gunze lacquer thinner. Some of the self lacquer thinners are too aggressive for use with Tamiya. If you thin less(1 part paint to 1 part thinner) you will need more pressure as with all paints.

Graininess is usually an indicator that the some of the paint is drying before it gets to the surface or that turbulence from air swirling in tight corners is depositing overspray back on your model.

Test your spray on scrap plastic before you shoot your model and check for good atomization and then watch your angles. Always remember, the coat you spray should go on wet and then dry, it should not look dry as soon as it hits.

Hope this helps,

Paul H

I agree with Paul. It sounds like there is too much thinner for what you are doing. If you are doing fineline work, thinner is good. you are painting closer to your work and you have reduced the volume of paint you are using. However for regular work at normal distances on a dry warm day it might be too much thinner. Because you said it only happens occasionally I don't think it is an issue with the airbrush. Pressure issues are quickly resolved. Spray a test pattern. If there is an issue and you think it is pressure then up the pressure to about 20 lbs and try a second pattern.

The graininess is usually due to the fact that the atomized paint is actually drying just before or just as it hits the surface. When you spray the paint it should hit the surface wet(it will look shiny)and remain so for a few seconds. It should not pool or puddle. The solution to graininess is to either work closer to the surface so the paint is still wet on contact(less distance to travel) or increase the pressure(decreasing travel time). It could also be an issue with the paint to lacquer ratio, there being too much lacquer causing the paint to dry too rapidly. I have been painting with Tamiya paints almost exclusively for over 30 years and have not had this problem since I started to use them and figured out the proper paint to thinner mix. Good luck.

Bear in mind that the pressure measured at the compressor is unlikely to match that at the airbrush, as there is a hose between them whose length, thickness and leakiness will affect the pressure at the airbrush.

Thank you for your replies... Paul has made me think about the turbulence effect.. I do sometimes notice a kind of a cloud around the model while I;m painting because I have a box type thing around it to protect the desk.. just didn't occur to me that this might deposit on the model itself and cause this graininess

As far as the thinning goes, based on what I read and heard in videos, I'm using around 60:40 or maybe 70:30 thinner-paint.. does this count as too thin? What is considered to be the "regular" ratio?

Also, the distance.. what do you guys consider to be a "normal" distance for spraying? Problem is that for so many years I was used to using spray can paint.. so I guess I need to unlearn what I was doing before

By the way, do you use these same methods for spraying gloss colors? Because I haven't been successful yet at getting a smooth glossy surface when I tried to paint a couple of car models I have.


Thanks again
Hisham

I typically spray around 3-4 inches away from the piece but for detail work it can get closer but it has to be thinned.

Pressure and mixture is important since if you try and use a thick mixture on low pressure and close range, the AB is spraying more air than paint causing the paint to dry faster.

I usually thin 50:50 for tamiya but I think 70:30 is already very thin. I would use the 70:30 in really detail up-close work

The spray can puts out a ton of paint so you have to stay 8 to 10 inches away and keep the can moving or the paint will puddle on you.
With my air brush 3 to 4 inches distance is normal for base coats. For detail work I sometimes work at a distance of 1 inch or 3/4th inch with the pressure at about 5 to 10 pounds, paint thinned 60/40 and the needle is adjusted to only have a little paint flow.
I wouldn't spray in a box unless it was a spray booth type to pull away any floating paint particles and fumes.

Gloss is a world of its own. I use the same techniques but may add some paint retarder for acrylics to slow the dry time. You do not want it starting to dry before it hits the body. Get some 1000,1500 and 2000 grit sand paper and you will need to wet sand between coats. You will probably have 3 or 4 coats before you are done. Good gloss is a lot of work. I decal a car and gloss with clear. After 3 or 4 coats and sanding, the paint has built up enough so that there is no visible seam at the edges of the decals. I know on actual cars that the decals are vinyl and are not glossy but it is an effect I like.

Hisham,
Thinning ratios are also subject to change based on the airbrush you use. Spraying through a brush that has a cone type tip ( Iwata Eclipse etc ) requires less thinning compared to the smaller fixed nozzle type ( Iwata HP series). Experimentation to account for the brush you use and the area you live ( temp and humidity) will yield best results. Ratios you get from elsewhere, are only starting points.

Welcome to the fun of airbrushing!

Paul H

This short video might help with your pressure setup
https://www.youtube.com/watch?v=U5BAqPQCpGg

This one might give you some ideas for a smooth finish
https://www.youtube.com/watch?v=p2QPqwDV2ys

Paul

I have a 1/5 horsepower compressor with a 3 liter tank and an Iwata Revolution CR with a 0.5 nozzle.. and I was thinking of getting and Iwata HP-CP with a 0.3 nozzle for detail work and freehand cammo and stuff. My budget for another Ab is a max of around $140 - 150.. so, these are the models I found within that range. I got the Revolution for about $85 from Japan.. and it actually is pretty good for priming and base coats and general work like that.. I think I'm just still new at thinning and all that

Anyway, those are my limitations that I need to learn to work within

Hisham

This... the graininess is mostly distance related, not pressure related.

Just to echo what some others have said, thinner to paint ratios are not an exact science. Temperature and humidity, local conditions in general will effect the ratios. Also, different colors may require different ratios due to the pigments used. I find that gloss white and gloss yellow require more thinning as well as a retarder or flow aid, something I don't generally have to use with other Tamiya colors. Trial and error(unfortunately)and experimentation are really sometimes the only way to discover the right ratio. Good luck.

Like I said, I realize I need to experiment, but I needed some guidelines to go by... So, thank you all, I've learned a lot.

Hisham