Hi All
I hope I can find some experienced users here with what I am doing. I am spraying my solid guitar bodies. I made a small 4x4x8 paint booth. I have a draw fan pulling 1750 CFM. I use an Iwata LPH-80 124G mini gun. Iwata says to have 1 bar, (14 PSI) at the gun when the trigger is pulled. I do. I am spraying Mohawk instrument lacquer. I use Mixol colors. The gun hold 150ml and so 10% of that is the Mixol color and two full caps of lacquer retarder as well. I spray when humidity is below 50% and temps are 70 or above. I spray about 4" from the guitar. Iwata suggests between 2.5" and 5". The draw fan works well. There is no "cloud" in the booth. I'll spray two passes and call that one coat and then wait one hour before repeating for the second/final coat. (Mohawk suggest one hour between coats). However, after doing all of the above I am still getting a grainy finish. What am I doing wrong?

You are following instructions instead of watching the flow of the lacquer.

Sounds like not enough material is coming out of the gun. Do you have a bigger tip? If not keep thinning until you get a nice wet flow with your two passes. Don't use any more retarder than you are using now, use regular thinner.

Think of spraying as more of a sight thing, you need to see how much is coming out and how it flows out after it's on the substrate. Use the manufactures recommendations as just that - a starting point.

Don't be afraid to add more air, go as high as 35 psi. The more air the more material will be pulled out from the cup.

My question is, what should that flow out look like? Iwata suggests to minimize the amount of fluid to just what you need. They don't recommend wet coats. Also, the gun is made for 14 PSI, (which puts 10 psi at the tip), and they do not recommend above that as it may "damage" the gun. However, I see pro sprayers on line like the Gunman using it at 29 psi.

I would check with Mohawk as to how the finish should look when it hits surface, their product their science. Take a piece of material similar to guitar body and try different air to gun, different viscosities of material. No need to practice on instrument, no pun intended.

I'm with Leo here. Manuals are more like a "guide". Where are you measuring your pressure? At the gun or the compressor? I don't like a pressure gauge at the gun because of the awkwardness. So I have to run more pressure at the compressor. And I don't really even look at the gauge so much as I look at business end. You have to play around a bit with tip size, fan size, thinning, retarding, pressure to find a sweet spot. As a professional shooting mostly WB I try to spray as WET as I can without the runs and potential bubble issues. Dry is never good. Results can change with a new batch of finish or a slight change in weather/humidity. Also are you spraying vertical or horizontal? Big difference in how wet you can spray. Either way you could be getting some overspray on the 1st side.

Plus I'm thinking for a guitar an off the gun finish isn't gonna cut it anyway. I would think you'd have to rub it out to get that mirror type finish.

My2cts
cheers

So for my second coat of base I increased the flow a half-a-turn and I increased the psi with the trigger pulled to 20-21 psi. The result was a better coat. There's is some very slight orange peal but the dry spray was not present. I guess I will try next time to go a little higher like the Gunman's 29 psi usage. I don't like how the manufacturer's instructions are not as good my latest discovery. One other question, does retarder also reduce? I am assuming yes that it too does thin as well. I'm just curious now as to why I am getting slight OP. The viscosity is good and I have retarder in there. I should be getting good flow.

Stop thinking about all these recommended numbers and settings and start spraying test panels. Increase your pressure, test the pattern, adjust, do that 100 times til you get what you want.

No set of rules is going to "work". And the instant you say "cap full" your fouled. If you want to build a recipe for repeated small batch results, until youve mastered it, there is no "cap full". What is a cap full? Overflowing? Kinda full? Spilled a little?..

Invest in a gram scale that measures to .01 grams and start mixing your material that way.

Forget about pressure settings and look at whats coming out of the gun.

In the end... for instrument finishes.. who real cares? your going to wet sand the whole thing out and buff polish.. the only reason to try for a good layout is to minimize your wet sanding.

Stringed Instrument or Classic Instrument lacquers both say to apply a wet coat. The Classic says 3-4 mils which is a bit less than the 4-5 mils I usually spray with my conversion varnishes.

Wet spray is when all the small atomized particles on the surface start to join together. You'll notice it will go from a surface that looks very orange peeled to a smoother surface as time passes (10 seconds or so).

Open the gun up all the way, don't have the trigger limited, maximum flow. Adjust the air and fan so that you get a good wet pattern at a moderate pass speed. The faster you can get the whole surface covered the better results you will have.

Retarder is thinner, but it flashes off slower allowing the lacquer more time to flatten out. You have fast, slow and in between "thinners". Fast, regular, reducer, retarder and usually something slower than that, MLC calls them Flow Enhancer #1 and #2.

Hot and dry requires slower dry times so you can get the lacquer onto the surface. Sometimes you slow it down because the surface is large and you need more time to coat it and keep your wet edge.

If you are going to be wet sanding a slightly irregular surface doesn't really matter since you will be sanding and buffing.

Thanks all for the helpful replies. I'm going to try and experiment with all of your advice. I do have a couple other questions for the experienced. One, if my base coat has any amount of OP in it but I spray my CC really well and then buff and polish, will the base coat OP show through? Two, if my very first CC pass has OP in it, will no amount of wet sanding help? My theory here is that I would have to sand down to the first layer to level out the OP, which would then hit the BC. I have yet to see the next layer of lacquer melt and level the previous layer so I doubt multiple layers would fix the first layer. Your thoughts? And yes, hopefully this is rhetorical as I will be trying to spray as wet a coat as possible from now on, which hopefully produces zero OP.

One other quick thing. A proper light set up would be a big help. If you can safely set up a light to cross site the object your spraying you can pick up your wet lap and see your dry spots.

You shouldn't have to worry about overspray between coats because you are sanding between each coat which should eliminate any overspray.

You stated a Iwata mini gun
Do you know the nozzle size?
Usually when it's called a mini or touch up spray gun,it has a small nozzle.
If it's too small,it will give you dry spray if you move too fast

It's a 1.2 sized tip

1.2 mm
Just what I suspected
It's a bit small to spray what you are using but doable
Those small guns are good for touch ups or narrow strips
Larger surface are more challenging
Try to move slower and do a 70% overlap rather than 50%
Keep it wet!
The fan pattern is not really wide with those guns so be patient!

It can go to 5" wide but I try to keep it around 3". I'm spraying a solid body that's 12" wide and the sides are 1.75" wide so I figured a mini gun, with it's low psi requirements, would be perfect. Here's the guitar. PS: Except for the tuners I also make all the hardware and pickups. The bridge is my own tool-less design.

View higher quality, full size image (1125 X 1110)

One other question. Leo mentioned sanding inbetween coats. With regards to base coats I would not do that. To me they need to go on perfect and untouched. I have had success in the past with that. However, I figured with the clear coats that I only wet sand after all my coats are on, (and two weeks gassing off time have passed). You all sand inbetween each clear coat?

VERY NICE!
Personally I would invest in a standard spray gun
The large surface is a little too large for the spray gun you use

To answer your last question
I do sand between coats
Sand by hand only
I use 220-320 grit
Then my last coat goes in smooth

How long do you wait to spray between coats? I am waiting one hour. With sanding inbetween coats, are you wet sanding? What method of cleanup are you using? Air and tack cloth?

I use a different finish than what you are using
I mostly use pre-cat lacquer and conversion varnish
The stuff dries really fast and I can recoat in 1 hour
Sometime when the weather is really nice I can get away within 1/2 hour!
No wet sanding
Just hand sand with 220-320
Then I just blow.dust with high pressure air
Then proceed with next coat
But when using a catalized product you can't go with too many coats
2 for CV and maybe 3 for pre-cat(top coat)
No more than 5 mill dry total

Both descriptions of spraying the Mohawk lacquer says to sand between coats. Since it's a modified nitrocellulose coats will melt into each other.

With a conversion varnish you need to have a sanded surface for proper adhesion. If you spray wet on tack you can get away with it.

Guitar guys typically use regular size gravity guns.

Woodworkers typically use the mini guns for spraying things like stain. It’s watery so it goes thru a 1.2 tip. As Leo wrote we run them at almost normal pressures(30psi). Everything is set wide open. With the stain it gives very good control. Basically dusting it on until you get the correct darkness. HVLP hi-transfer guns are typically run at (40-45psi).

You get chemical bonding when the finish is green. You get chemical & mechanical bonding if sanded in the green window. You get mechanical bonding after the green window if sanded. No bonding if not sanded.

In reality the bonding is a nonissue. The issue is dust, orange peel & runs. If none of those are present many people will go coat to coat within half a day.

We all work in a dusty environment. We are woodworkers. It’s very hard to keep a perfect spray room. We also spray some oddly shaped products. All of those contribute to the need for a quick scrub between coats(320 grit)

Quite a few people have mentioned your problem is most likely your tip size, 1.2-1.3 is to small for lacquer.

Let’s say you host a party at your house, Unble Bob goes to the toilet and uses way to much toilet paper, we all know what happens, the toilet gets plugged, to much material trying to fit through a hole that is not big enough.

Your tip on your gun is way to small for the material you are using.

I would recommend buying a Sata 100 gravity fed gun, with a 1.9 tip. They are fairly reasonable and you will end up with beautiful results,
I read about the Iwata gun you are using and it is a great gun, but it appears to only have tip sizes for automotive painting.

With your air turned off you should get a nice stream of material coming out when you pull the trigger, then you adjust your air to get a nice pattern. I read your other post as well and I would maybe try a little less pressure, as for air flow from your booth , I wouldn’t worry about that, a professional booth had an air flow of 100 lfm, or is to have 4 air exchanges in a minute.
Just be careful, home made spray booths and solvent based finishes are a recipe for disaster.