Getting the right PSI


TurboGuru
03-16-2010, 10:18 AM
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
03-16-2010, 02:33 PM
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
03-16-2010, 03:39 PM
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
03-16-2010, 03:42 PM
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
03-16-2010, 04:25 PM
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
03-16-2010, 05:40 PM
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
03-16-2010, 08:29 PM
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
03-16-2010, 10:09 PM
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
03-20-2010, 07:34 AM
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!! :grinyes:

stevenoble
03-20-2010, 09:40 AM
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
03-20-2010, 01:32 PM
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
03-20-2010, 02:00 PM
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
03-21-2010, 04:49 PM
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
07-26-2010, 04:12 PM
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...:runaround:

Typical crappy results airbrushing with Zero Primer:
http://img714.imageshack.us/img714/9896/dsc01957z.jpg


Tamiya Fine Grey Primer - 1hr dry no sanding or polish (raw)
http://img811.imageshack.us/img811/2407/dsc02007clean.jpg

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! :smile:

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

MidMazar
07-26-2010, 04:48 PM
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.

Macio4ever
07-26-2010, 05:25 PM
I would consider to use a retarder to reduce evaporation rate of the paint/primer. I usualy don't have big problems with color paints but primer (Tamiya) tends to dry too fast and become grainy.
Mr Retarder Mild is a good addition.

I tend to keep low psi (about 20) and thin paint well. I noticed that many of us (including me) are afraid of too thin paint which is wrong as too thin paint is far better than too thick.

I also suspect that Tamiya bottled Surface Primer is different then Spray Surface Primer Fine - I mean it is not as fine as spray one.
I have to try bottled Mr Surfacer 1200 and we will see...

TurboGuru
07-26-2010, 05:41 PM
Yes I have heard about Mr Surfacer being another good primer, its better than Tamiya which I find hard to believe right now but I'm sure it is.

Decanting is a good option, my only fear is having the solvent evaporate over time.... I do have empty glass jars so I should be ok?

Macio, I have started thinning my paints a little more as you say, and it does feel much better, even fresh Zero paints from Hiroboy I added a little extra basecoat thinner and it comes out really nice.

So you spray at 20 PSI? Is that the same for Zero Paints if you use them?

I've not sprayed Tamiya acrylic paint through my airbrush, but I know from brush painting just how quick that stuff dries.

So a retarder I'm guessing is some sort of acrylic agent that will slow down the drying time? Any suggestions on a brand?

Finally.... is the Tamiya Primer a lacquer based product? Just trying to work out why it has given such a lovely finish.

Macio4ever
07-27-2010, 02:59 AM
TurboGuru,

20 psi is most often used and I lower psi for small jobs and 0.2 nozzle and a bit highier for more air demanding AB with 0.5 nozzle. I think there is no one right value. If you need to paint with thicker paint you have to up pressure to avoid spitting and you may lower with reduced paint. Generally I prefer lower psi to avoid air drying paint which may end up with orange peel.

I dont use Zero however I use other automotive paints. Tamiya acrylics spray excellent with given psi! They are imho together with Gunze C paints the best avaiable.

GSI (Gunze) - Mr Reatrder Mild is a retarder I have used. It is for "C" paints which means that it will probably work with other lacquer based paints.

Yes., Tamiya Surface Primer is lacquer based as well as Mr Surfacer.

stevenoble
07-27-2010, 10:37 AM
That surface texture you have using the Zero primer is typically what I was getting when I used it. I tried many combinations of thinning and psi and never solved the issue. That's why I switched to the Tamiya primer. It is expensive but the finish is light years better than the Zero primer gave. Worth a little extra expense I feel and I don't build too many models these days due to time and the fact my hearts not always in it......

TurboGuru
07-27-2010, 05:27 PM
yeah steve, its fantastic, such a shame about the zero primer because their airbrush paints are very good.... I suppose they can't be a jack of all trades!

I would be willing to try some of the Mr Hobby primer too but it seems so damn rare to find. Surprisingly I found little on ebay either!

Macio, thanks for confirming that the Tamiya Primer is lacquer based, I'm starting to understand why people love synthetic-lacquer based products now.

UKPonchoMan
07-28-2010, 02:40 PM
One thing to add - DO NOT spray any car-based metallics over Tamiya primer - they'll eat right through it AND the plastic underneath... You can get away with solids though...

Now go on...ask me how I know!!! :(

drunken monkey
07-28-2010, 02:52 PM
One thing to add - DO NOT spray any car-based metallics over Tamiya primer - they'll eat right through it AND the plastic underneath... You can get away with solids though...

now that's a bit too general.
i've used these (http://www.autopaintsbrighton.co.uk/hycote-double-acrylic-car-paint-aerosol-150ml-factory-colours-ltd-range-512-p.asp) over tamiya primer with no problems.

example:
http://xd5.xanga.com/a12f35f638031252029615/w200155178.jpg (http://www.automotiveforums.com/vbulletin/showthread.php?t=962163)

UKPonchoMan
07-28-2010, 03:04 PM
Very nice!

I've made the same mistake several times with Zero paints and found out the hard way... other paints might be more forgiving... I'm guessing it has something to do with the amount of carrier in the paint vs solids...

TurboGuru
07-28-2010, 05:28 PM
One thing to add - DO NOT spray any car-based metallics over Tamiya primer - they'll eat right through it AND the plastic underneath... You can get away with solids though...

Now go on...ask me how I know!!! :(


Interesting, well earlier today I sprayed some 'White Aluminium' by zero onto a piece that I had coated in Tamiya Fine Primer...

http://img37.imageshack.us/img37/9823/dsc02016j.jpg

I've not noticed any eating of the plastic? Looks great!

Macio, I know you said there is no exact PSI to use, but I tried 20 anyway with some extra thinning of the zero paint and it went on great so I think I have found a PSI that works well for me :)

So I now need to apply the zero 2k clear coat... my first time using it!....

One thing I'm really looking forward to is the fact that 2K will not shrink as it cures - I've seen this happen on the 1k stuff, not pretty!

The general consensus seems to be that you need to spray clear coats at a much higher PSI.... considering I am firing my acrylics at 20, I'll test it at 30 PSI... what do you guys think?

drunken monkey
07-28-2010, 05:56 PM
i think you should test on spoons.

from what everyone says, you're not really going to being to 100% replicate their thinning and/or airbrush techniques so why not do your own batch of testing to see what works best for you?

TurboGuru
07-28-2010, 06:02 PM
i think you should test on spoons.

from what everyone says, you're not really going to being to 100% replicate their thinning and/or airbrush techniques so why not do your own batch of testing to see what works best for you?

Already tried that and yes it does help (spoons)... but sometimes seeing what others do can accelerate that process....for me at least.

Take Macio's tip of 20 PSI, I tried that and it worked perfectly.... I'm asking specifically about the 2k clear PSI because I'd just like to know what people spray it at.

I have some spoons with basecoat applied ready for 2k... I'd rather be 'on the right track' than trying to find the track if that makes sense, 2k aint cheap and it isn't easy to undo once on...... unless the IPA theory stands true.

http://img826.imageshack.us/img826/2679/dsc01928a.jpg

drunken monkey
07-28-2010, 06:12 PM
well, the biggest thing is that people can only describe what they do with their paint.

you have no idea how evaporated their paint is when they add thinner, you might not be using the same thinner; your idea of "milk consistancy" might not be the same as theirs, you in all likelihood spray at a different distance and at a different pace, ambient spraying temperature is going to be different, humidity, paint temperature, all different and all have an effect on painting.

what works for one at 20psi might not work for another.
however, what you find works for you will work for you but here's the kicker; it might not always work either.

get my point?

TurboGuru
07-28-2010, 06:59 PM
I get your point....

For months and months I tried to get Zero Primer to work properly, I tested endlessly at different pressures, adding thinner, change spray distance, all the main variables.... only to find the primer still goes on like crap.

If it wasn't for some of these members such as Steve pointing out that he has also had the same problem with Zero primer I would of just given up. In this instance had it not been for Steve's comment I would of carried on thinking I was doing something wrong with the product no matter what variable I changed.

I have tried spraying 1k at 20 PSI, it didn't turn out so great, solids started seeping through, this was after adding thinner too so the comments about clear coats needed a higher PSI do seem to be accurate.

I've checked the instructions for 2k and cant seem to find the PSI range they suggest so I'm just asking...

Didymus
07-29-2010, 03:33 AM
Tamiya Primer is beautiful stuff, but I only spray it straight from the can. (Actually, the bottled stuff also makes pretty good light putty.) If you like Tam primer, you'll love automotive urethanes. They have a similar smooth, grainless coat if they're thinned properly.

As to AB pressure, it's the one thing I rarely touch. For me, the main variables seem to be viscosity, spraying distance and nozzle adjustment. Because I seem to get the best results by spraying thin paint from a very close distance, I sometimes need to adjust the nozzle to restrict the flow. When you spray as close as I do - 6 inches - a nozzle adjustment can help avoid drips and sags.

I really have to be quick when using a spray can. But the results - a smooth finish with minimum orange peel - are worth it.

I've never had a problem spraying automotive urethanes over Tamiya primer.

TurboGuru
07-29-2010, 03:39 AM
Thanks for the reply didymus.

With Zero products I have found that changing the PSI is a must... 20 PSI for me is working well with their normal basecoat paints, but it doesn't seem to work well with 1k clear.... the clear comes out all gooey and in spits.... requires too much thinning at this pressure... bumping it to 25-30 PSI solves the issue for me.

Your suggestion using 'automotive urethanes' is very appealing - With it being urethane based I'm guessing the paint won't have a shrinkage effect as it cures?

Only issue is how would I obtain some automotive urethane paint in small quantities like zero paint?

Didymus
07-29-2010, 11:29 AM
Your suggestion using 'automotive urethanes' is very appealing - With it being urethane based I'm guessing the paint won't have a shrinkage effect as it cures?

I've never noticed any. It has great coverage, so it can be laid on thinly. I usually use only two-three coats, depending on the color and primer.

Only issue is how would I obtain some automotive urethane paint in small quantities like zero paint?I buy it at my local Finishmasters store. They're in many cities; they're a paint vendor to body shops. A two-ounce touch-up bottle, mixed to order, costs $14, including a buck for the bottle. I thin it approximately one-part paint to at least one-part medium temp reducer, but different paints seem to need different ratios. And the paint thickens with age, probably because I'm not very good at sealing the bottles. Regardless, the thinner you can apply it (and still get drip-free coverage), the better.

The AUs provide a satin finish, and need to be clearcoated. I don't use 2K; I'm perfectly happy with U-POL Power Can clear, which I've talked about many times on the forums.

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