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Discussion Starter · #1 ·
Hi Guys,

So I've been working on a sprayed lacquer project for a few weeks now. I'm on the finish and, I'm working through some issues.

I've done a ton of research and I have a good handle on just about every aspect of the system except I don't FULLY understand how to calculate my required viscosity. I get the idea but all I have to work on is this.

My paint (sherwin williams opex product finish) says only two real things about viscosity. Neither mention anything about the gun nozzle size.
* 20-25 seconds #2 Zahn Cup at 100% reduction with R7K120
* For HVLP System reduce 50-100%

I experimented first time around with a cheap harbor freight 1.7mm gun and 75-100% viscosity and I got OK results but I'm now trying to re-evaluate and finish this project right.

I went and bought a Sharpe Finex FX3000 gun with a 1.4 and 1.8mm nozzle.

My thinking is to use the 1.8mm to lay down the primer (for the white pieces) and the initial layers of clear on the clear pieces. Then later smooth the surface and move down to a 1.4mm for the final layers using a higher ratio of thinner.

Now here's where I'm stuck. I know the viscosity requirements will be diff for the 1.4mm and 1.8mm needles but I can't find any definitive information on it (just checked my gun manual). I'm really trying to avoid trial and error again since I don't want to sand anymore poorly laid down primer off my pieces.

So, the questions are. General answers are great but my questions are specific to lacquer

  • what type of Viscosity cup do I use?
  • how do I tell the viscosity to needle size?
  • how does the actual product thinning information affect viscosity to needle size requirements?

many thanks!
 

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I kinda think you are overthinking the mixture. I've never owned or used a viscosity cup. Every different line of lacquer thins different and some come already packaged to spray. You should be able to use one mixture with any sprayer tip you are using. I often use the Promar line of lacquers from sherwin williams and I mix 16 oz of the lacquer with about 10 oz of lacquer thinner. The idea is thin it enough that it will barely spray a wet coat. It wastes time and thinner to overthin it and sometimes overthinning it screws up the sheen on the finish coat.
 

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Discussion Starter · #3 ·
so whats your rule of thumb for what's a good layer?

Keep in mind I haven't yet actually put down a good layer of lacquer so I'm kind of shooting in the dark. I keep either going too dry and getting orange peel or laying it down to thick and getting sags
 

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so whats your rule of thumb for what's a good layer?

Keep in mind I haven't yet actually put down a good layer of lacquer so I'm kind of shooting in the dark. I keep either going too dry and getting orange peel or laying it down to thick and getting sags
I don't know if you can actually measure a layer. If you are getting orange peal you are close to having the mixture right but needs more thinner. Until you get used to the feel of the mixture it would be good to measure the solvent you add and keep a record. I can tell when I'm stiring the finish if it is thinned enough or not. When you spray it, it's best to put a wet coat of the finish on so that it will flow out before it sets up. You kinda have to push the limit spraying it. There is a fine line between having it right and having runs in it. It's just something that takes practice and all of us get runs in the finish once in a while. If possible spray everything laying flat until you get used to it. Then you have to overlap the row of spray with the previous row because the finish dries so fast that to get a uniform sheen you have to always keep a wet edge until you reach the end of the panel you are spraying. Think of the way roofing shingles are laid as you are spraying.
 

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Sawdust Creator
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I tried spraying lacquer with an hvlp gun...then I switched to using an airless sprayer and spraying with no thinning....never looking back!!!!
 

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In History is the Future
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[...]When you spray it, it's best to put a wet coat of the finish on so that it will flow out before it sets up. You kinda have to push the limit spraying it. There is a fine line between having it right and having runs in it. It's just something that takes practice and all of us get runs in the finish once in a while. If possible spray everything laying flat until you get used to it. Then you have to overlap the row of spray with the previous row because the finish dries so fast that to get a uniform sheen you have to always keep a wet edge until you reach the end of the panel you are spraying. Think of the way roofing shingles are laid as you are spraying.
+1

I started with a 1.5 then to a 1.4 then did some research that suggested 1.6-1.8 was ideal for lacquer and after buying a couple 1.8's I would have to agree. With a 1.4 you have to thin so much that you will have trouble keeping a wet edge without runs. A 1.8 works well for me. I spray lacquer primer through a 1.5 but all other lacquers go through a 1.8 - clears and pigmented.

I've never used a viscosity cup in my life.
 

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Discussion Starter · #7 ·
hmmm guess I'll just spray lots and lots of test wood.

sucks that it sprays so fast I find myself running out of new surfaces to paint!

thanks guys, this forum is really fantastic
 

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hmmm guess I'll just spray lots and lots of test wood.

sucks that it sprays so fast I find myself running out of new surfaces to paint!

thanks guys, this forum is really fantastic
Quit practicing on scrap wood. It's just paint. If you get orange peal or runs it will sand out and you can coat over it. It's different with a stain when you get the color wrong it's hard to fix but paint is easier to fix.
 

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Discussion Starter · #9 ·
Quit practicing on scrap wood. It's just paint. If you get orange peal or runs it will sand out and you can coat over it. It's different with a stain when you get the color wrong it's hard to fix but paint is easier to fix.
except you gotta let the stuff dry and then you gotta sand and repaint, such a PITA.

I just want it to look good and BE DONE
 

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Old School
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Spraying paint can be made as complicated as you want. I've never used a viscosity cup, and if I changed needles and tips on a spray gun...I just can't remember.

What I do is mix up my potions, and spray on a sample...adjust the gun, and spray the project. With a little practice, getting a good finish is getting the gun and air adjustments right, and exercising good spraying techniques. It's more experimenting and practice than anything else.






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Rick Mosher
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I do have a viscosity cup and I know how to use it. Do I use it every day? No. I use it when there are problems with the finish or we are setting up new equipment. I also have a wet film thickness gauge and I know how to use that too. If you are using conversion varnish type finishes the dry film thickness is critical or the finish can shatter like cheap glass.

A viscosity cup is nice to have when you're learning because you can see the relationship temperature has on viscosity. When it's hot out the material is thinner than when it's cold out. So that tells you to use more thinner in cold weather and less when its hot.

You don't need any of that for home use though. I would take 8 oz of finish and spray a small sample without thinner and then add 2 oz of thinner and respray, keep doing this until you get a perfect finish, (looks like glass when wet and dries the same) Keep track of the room temperature and write down that mix. Next time you will have a good idea where to start and if it is colder add a little more solvent. (slow evaporating solvent in summer fast in winter)
 

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I do have a viscosity cup and I know how to use it. Do I use it every day? No. I use it when there are problems with the finish or we are setting up new equipment. I also have a wet film thickness gauge and I know how to use that too. If you are using conversion varnish type finishes the dry film thickness is critical or the finish can shatter like cheap glass.

A viscosity cup is nice to have when you're learning because you can see the relationship temperature has on viscosity. When it's hot out the material is thinner than when it's cold out. So that tells you to use more thinner in cold weather and less when its hot.

You don't need any of that for home use though. I would take 8 oz of finish and spray a small sample without thinner and then add 2 oz of thinner and respray, keep doing this until you get a perfect finish, (looks like glass when wet and dries the same) Keep track of the room temperature and write down that mix. Next time you will have a good idea where to start and if it is colder add a little more solvent. (slow evaporating solvent in summer fast in winter)
Could you school him on the viscosity cups. I was just trained without one and never seen the need for one. Since he has nobody to train him the viscosity cup might help.
 

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Discussion Starter · #13 ·
I spent a good 6 hours last night on this. I found that if I was at about a 50/50 mix (this is for a really thick primer), it was a bit like a thick milk. Then that would spray pretty well.

I pretty much narrowed down my problem to a bad fan pattern that was causing the spread to be too great for a good atomization. Also had my wife follow me around with a hand held LED light so that I could see the white primer atomize (white on white, sucks).

I just gotta figure out a good method for spraying edges without over spray -- but for now I'm just doing all the edges first.

I ordered a Ford #4 cup for reference, and it sounds like for the stuff I'm doing, which is Lacquer, it'll be mostly trial and error with taking notes.

Anyway, maybe the "just go spray" advice is what I needed, thanks guys
 

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Anyway, maybe the "just go spray" advice is what I needed, thanks guys
That's what I suggest. Once you start to spray on a sample, you'll see what's happening. Of course experience will tell you what to adjust depending on how the media lays down. There's a lot to pay attention to, and some of the fixes are connected to the same problem.

Generally, once you try a certain mix, and get the air pressure to the gun set, and get the gun set, from there you have fluid flow, air adjustment, pattern, distance from the subject, movement speed, and spray angle. In order to get a nice finish, any one or all of those will likely need some adjustment.

You could practice with just water, but, water has no initial tack to speak of. But you can see the changes with fiddling with the adjustments.






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Rick Mosher
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Over spray is caused by a couple things,

1. Too much air pressure, this causes a huge cloud of over spray and it goes everywhere causing a gritty feel to the finish. Experiment with your setup and find the lowest air pressure you can use without getting orange peel.

2. Not spraying in the proper sequence and not paying attention to where the over spray is going. For instance inside a box the last thing you would spray is the bottom of the box or you will get over spray on the bottom when you spray the sides. On your edges you will need to keep the gun over the main surface and angle your spray slightly so no over spray strikes the edges.

Here is a video showing how to properly use a viscosity cup.


Also HVLP is very sensitive to volume or CFM of air. I hope you have a compressor large enough to supply enough CFM for the gun you have. Larger inner diameter airlines are recommended as well.
 

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Write notes.....once you have established mixing routines.Dosen't have to be a book,just the facts.Keep them in a folder near your paint bench.

One small tidbit I can add to above,to the point I wrote it on a pce of masking tape and stuck it above our mixing bench.
"move the dry spot around".IOW's if you map or plan out your spraying routine......start with edges,then shoot this direction...then around here,etc.etc.There will inevitably be "dry spots" which are simply misdirected overspray that you have no control over.You're trying to be as thorough as possible in eliminating "dry spots",but it's going to happen.The "trick" is....move the dry spots around.

Continuing to follow the exact same routine or plan(always spraying this 1st,then that,2nd)...the dry spot will always have more or less material than other areas.And a very good reason to minimize the number of coats.Before each spray,unless it's something like a cabinet door thats been repeated a thousand times.....I do a dry or practice run with an empty gun.Trying to get a feeling for where unwanted overspray is going to end up.The more complex an item's shape,the more this happens.
 
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