Getting the right PSI

[TurboGuru]

Equipment:

Iwata Smart Jet Pro Compressor
Iwata Revolution CR Airbrush (Dual Action/Gravity)
Iwata Revolution SAR Airbrush (Single Action / Siphon)

A few months ago I did a search on this forum for tips on buying an airbrush and accessories, there was some useful information which helped my make the decision to purchase the equipment above.

However, information regarding what PSI should be used for models (1/24) just confused the hell out of me.

Some modellers spray at 10-15 psi whilst others spray from 20-30psi!

Most of my paint jobs have come out 'ok' but I have a real hard time with white primer, this very occasionally gives me 'grainy areas' which are a nightmare to sand out - grey primer is absolutely fine though along with paint.

I think this is because the PSI is too high perhaps? causing the white primer to dry before it arrives on the model? ( I use 25-30 psi)

10-15 PSI just doesn't work well with the SAR airbrush, its forever spitting our the product, I think this is because it is a siphon-fed airbrush so I need a lot more PSI...

The CR-R seems to cope with 10-15 PSI well, its gravity fed - Only problem is its nightmare to use on my hands, horrible cramp even with the pistol grip addon.

I'm in the process of buying a Iwata TR-2 airbrush, they are dual action but most importantly for me they are trigger based - general reviews seem to indicate it is very comfortable and its gravity fed meaning I can go down to lower PSI.

So is the general rule..... "Spray at the lowest PSI that is possible"?

Thanks guys

[CFarias]

What type/brand of paint are you using? What's your thinner?

As for me I decided to stick with a constant psi and modify my paint and thinner ratios for it, but make exceptions for metalizers and other special applications. If you are using compressors with fixed psi's then I would highly recommend doing the same.

The grainy finish of the primers may either be too high psi or not enough thinner -- both can have the same effect. If you are spraying at a fixed psi then you'll have to adjust the primer. I use an automotive grade primer in a can that is already pre-thinned, but I still have to thin it out to a milk-like consistency as I do my paints. I use acetone to thin the primer which seems to give me a smoother appearance than if I use lacquer thinner.

Ultimately you'll will probably have to do a lot of trial and error work even after the good advice you're sure to be given from the people on this forum.

[CrateCruncher]

I'm not an Iwata user so can't comment about that....

However, solvents are not all the same and can have a huge effect on paint performance due to their volatility (i.e. evaporation rate). Shooting any paint with an acetone solvent is difficult because it wants to dry partially in the air due to the high volatility. High gun pressure makes the problem worse because it increases the droplet velocity which increases volatility further.

Ranking volatility of the solvents commonly used in modeling from high to low would be: acetone, lacquer thinner, alcohol, paint thinner (mineral spirit), water.

Of course this is just a rule of thumb and many reducer/solvents are available in different levels of volatility but that's getting into the weeds a bit. Bottom line, if you're white primer is giving you texture fits even after lowering pressure and additional thinning maybe it's time to switch to a less volatile primer.

[TurboGuru]

Thanks for the reply.

I can adjust the pressure on my compressor, the products I use are ZERO from Hiroboy.com. They arrive 'pre-thinned' ready for airbrushing.

I suspect that the white primer issue might be down to the high psi which I usually spray at 25-30psi

The consistency of the white primer appears to be between millk and semi-skimmed milk. I have some Zero based thinner so next time I might add a little extra and low the pressure.

[CFarias]

CrateCruncher makes a very good point about the volatility of the solvents and how they affect your paints while using an airbrush.

Let's here from the Zero paint users and see what they recommend.

[Some_Kid]

You just need to experiment with your thinning ratios. 15-18 psi, and maybe to 22 or so will be the range that most paints will/should be sprayed in. It also depends on the finish your trying to get. But anything tamiya or testors is probably going to be in that 15-18 range. Alot of times you can get away without thinning if these are fresh paints, this is particularly true with testors acrylics.

Try spraying the primer at around 20 psi at most with the CR. I have the CR and a Kustom Eclipse with an adjustable compressor.

[stevenoble]

I thin the Zero paints a little more instead of using them from the bottle as I find that although they are pre-thinned they spray better for me with extra thinner added. I use quite a high pressure around 25-30 psi for colour coats and 40+ psi if spraying clear coats. I'm using a Tamiya HG wide trigger airbrush with a 0.5mm tip size. It's very similar to the Iwata TR2 that you mentioned. I stopped using primers through the airbrush, because I had the same problems that you have mentioned and no matter what I tried, I couldn't solve them. I use Tamiya aerosol primers now, white and grey, for all my priming needs.

[MidMazar]

I typically stay with 15-20 psi with almost all my paints. With laquers a tad bit lower. Also whenever i upped the psi to 25-30 i would get a grainy texture. But like stated before, ratio really has to be spot on also.

I have an iwata and never had problems with the pressure, only ratios. Just try different psis until something works. I haven't used zero white primer, but ive heard of other people having some problems with them. Good luck.

[TurboGuru]

Thanks for the advice!

Generally I have no problems at all with ZERO products except for the white primer, so I might have to switch to using the Tamiya Fine white instead.

The TR-2 arrived today, no hand cramp and I tested it on a spare part, the paint came out lovely and smooth at 18 PSI!!!! .... its an expensive airbrush bit its giving me great results already!!

[stevenoble]

I've been doing some painting these last couple of days (Fujimi Ferrari F187/88C) The paint went on nicely but I struggled with the clear coat. The first attempt came out terrible, so much orange peel texture, probably the worst I had ever done. I let it dry and sanded it back with fine wet and dry. This morning I reduced the pressure to 25 psi but more importantly added a lot more thinner. The results were worlds apart. Almost smooth enough to need no polishing at all. It does pay to experiment with different pressures and thinning ratios...

[KevHw]

I've been having problems spraying metallic zero paint in that it sometimes would just occassionally spit or nothing would come out. I added more thinner and passed a little air through the cup to help stir up any metallic flakes but it is too thinned and mostly thinner comes out. It also has a wierd effect that when I reduce the flow, I get a quick burst of paint going through. When people reccommend a consistency of milk, that also confuses me as milk itself has many varieties and densities (semi-skimmed, whole etc). My compressor doesn't have a gauge and it's not the most powerful (compared to the videos on Youtube I've seen). What are your tips for spraying metallics guys? Any help?

[Lownslow]

Originally Posted by KevHw

I've been having problems spraying metallic zero paint in that it sometimes would just occassionally spit or nothing would come out. I added more thinner and passed a little air through the cup to help stir up any metallic flakes but it is too thinned and mostly thinner comes out. It also has a wierd effect that when I reduce the flow, I get a quick burst of paint going through. When people reccommend a consistency of milk, that also confuses me as milk itself has many varieties and densities (semi-skimmed, whole etc). My compressor doesn't have a gauge and it's not the most powerful (compared to the videos on Youtube I've seen). What are your tips for spraying metallics guys? Any help?

get better compressor or get a regulator this will solve a majority of the problem, it should be the consistency of whole milk. it also sounds like your airbrush might be clogged.

[CifeNet]

I set my psi, mixture, and the brush setting, etc to my liking and then I shoot 2~3 minutes on a junk kit surface to confirm; this minimizes any unexpected result for me.

This is when I also add thinner or increase/decrease psi depending the result outcome.

And I don't clean my airbrush as often as I should, so it helps me to confirm before the actual shooting to make sure that everything is in working order.

[TurboGuru]

UPDATE.

Hi all

I have an update on this issue and thought I'd share with you some of the progress I have made...

I mentioned how I was struggling a lot with applying Zero Primer (grey and white) through my iwata airbrush. In particular I was getting some serious grain... sand sized grain!

In the past couple of months I've tried everything from increasing/decreasing PSI to introducing more thinner (cellouse based) to the primers...

thinning the primer and lowering the PSI right down to 12-13 PSI does bring decent results, but this is only ideal for small parts and not something like the size of a car body because you have to keep the airbrush soo close due to the low PSI.

Turn up the PSI and I noticed the graining starts to settle in, especially in crevices and get this..... on the hood, yes I don't know what it is but nearly every single model I've applied primer too always gets graining on the hood... must be something with my technique?

Once when I was spraying some of the primer onto a car body I looked very closely and could actually see the primer instantly drying on the surface, giving the grainy texture... rapid evaporation rate of solvents?

I paint in a spray booth with an extractor btw.

I almost came to the point of giving it all up... I've tried immensely hard to get this right, spent a lot of money on good equipment (airbrush/compressor) and getting shitty results.

Then I recall 'Steve Noble' mentioning in this thread that he had experienced the same issues and started using Tamiya Primers (Fine).

At the time I acknowledged Steve's advice but just felt cheated... I bought an airbrush/compressor so that I wouldn't need cans anymore, this includes primer.... and seeing how expensive Tamiya primers are only put me off more and so I continued to work with the Zero primers..... without success.... until this week...

This week I bought a can of Tamiya Fine Surface Primer for £9.99 and tried it out...

HOLY SHIT - this is what I'm talking about, it went on lovely, soo smooth even without sanding, this is how it should be, what a wonderful product...

Typical crappy results airbrushing with Zero Primer:



Tamiya Fine Grey Primer - 1hr dry no sanding or polish (raw)


You can see clearly the difference here, the Tamiya primer went on so smooth leaving me with a lovely finish which will only get even better one wet sanded.

The grain seen in the lambo picture is typical of what I have had with the zero primer for the past few months, each time I sand it, recoat to find the same problem, and in crevices its even worse because you can't reach those parts soo easily to sand them out.

What's important to note here is that the Tamiya primer was sprayed in the same booth as the zero primer, temperature was very similar.

I could really slate Zero Primer but to be fair it does come out quite well under really low PSI, 10-14.... this makes it perfect for close up work on small parts and so I will continue to use up my current supply of Zero Grey Primer on very small parts with a low PSI.... using the Tamiya can would be a waste as I can't control the pressure of the can. (I only remove parts from the tree when needed).

Thanks to everyone, in particular Steve for his suggestion, my faith has been restored!

All I need to know now is where can I buy 6x pack boxes of this stuff?

[MidMazar]

Mr.hobby primers are just as good if not better. Why don't you try decanting the tamiya primer and try shooting it through your airbrush? Maybe you will get the same results? Worth a shot and you won't be wasting primer like from the can. Good luck.