Hmmmm.....
Let me preface by saying this is my own practical experience, and anyone else's may differ.
First, a three stage gun/turbine like a Graco is plenty of machine to spray latex.
Time to woodshed the gun/material setup.
An HVLP is different from a an HVLP CAS gun, which is what most folks have. In theory, these are the same because they both use a lot of air at low volume. Similarites stop there. The "connected to my compressor HVLP gun" is simply a different look at the classic high pressure guns.
Yours (in my mind) is the real HVLP, although I do love my two CAS HVLP guns. The biggest difference is that almost all turbine guns use about 5psi pressure to push the paint in front of the air cap, as opposed to letting gravity or a 100% siphon system feed the gun. With that in mind, poor mixing technique can indeed introduce bubbles in your spray material. Not a problems with the old high pressure guns as they literally did atomize the paint, blowing into tiny droplets. After careful examination of a recently sprayed surface, you will see that turbine HVLP is more of a controlled splatter. Today's finishes are made with the sprayer in mind, and are most forgiving I have ever seen.
With all that in mind, here are my suggestions based on my 12 year love affair with my 4 stage Fuji HVLP, and a brief but productive affair with a pal's 3 stage Turbinaire.
- Toss out the Floetrol. That crap is relic of the past, and is only used by people like me when they have an open can that has started to cure. YOU don't need it. I haven't bought that stuff in 10 - 12 years, and no professional painters under 65 use it. Trust me, today's paint formulations assume a professional will be spraying. Call your coatings rep; he/she will confirm
- Make sure you are using the best quality coating you can afford. Sherwin Williams, Ben Moore, etc., all have a top line that is great. When using my buddy's borrowed Turbinaire three stage, I was able to spray the top line SW semi gloss enamel with no thinning. A lot has to do with particulate size, colorant, and the base material used in material formulation. (For example, SW is zinc oxide based, and Glidden is clay based)
- Try shooting without thinning. Could be a surprise there. If you need to thin, don't overdue it. (Although I have hit SW top line enamel 20% before with no ill effects!)
- Thin good finishes with filtered or distilled water. A gallon costs .99, and it will do almost five gallons of paint. Cheap.
- Turn the gun air OFF. Start a test shooting batch with a 10% thin. Open the coating feed about 3/4 of the way. Slowly open the air pressure till you get about a half feed. Spray a test area on a piece of primed or previously painted wood or sheetrock. This method won't work on bare wood. You should spray out a nice, but thin coat. In another area, open the the pressure valve a bit more, and see if you are still getting a good coat. Wait about 20 minutes and check to see if you have bubbles
- if you do, toss out the paint in the gun and clean it well. This shouldn't be a big deal since you are thinning by volume; you only need a small batch of about 4 oz each to get an accurate batch sample
- Reduce to a new mix of 15%. Repeat. While all guns and shooting conditions aren't the same, most seem to prefer about a 10% to 15% thin, with the pressure at about 1/2 to 3/4 open. I installed a regulator gauge on my gun though, as I couldn't always tell where I was with a face full or respirator. Since you are doing this professionally, I would strongly suggest you do the same for the sake of repeatability
- I have found that a 1.7 tip works best on my buddy's gun for latex, thinned as above dependent on spraying conditions. On my Fuji with a
1.8mm aircap, I spray enamels unthinned unless it is really cool where I am spraying
- Some finishes shoot betterhan others, so I would try a quart of top line products from different manufacturers and see which ones you like and your equipment like. I can't stress enough that unless your gun is actually broken, you have an excellent setup that you just need to practice and test with coatings to make sure you have it all as good as you can get.
- Watch your technique. HVLP guns are actually set to spray patterns similar to our old high pressure guns. If you are newer to spraying, it is important to find your gun's sweet spot. As a general guideline, for this kind of spraying, your aircaps will work best at about 8" from the surface. That isn't much, but it is also one of the reasons you have such efficient material transfer. It is also the reason you use lower pressure; the material doesn't have far to go. It is easy to hit the surface so hard you get bubbles. But think it through; a thinned finished with too much pressure will almost always yield bubbles.
An easy way to tell you have too much pressure is if you spray and find yourself in room full of drift, or you are using the same amount of paint as you do with an airless or high pressure setup. The bubbles are just another indication of too much pressure. It sounds to me like you haven't thinned enough, and your pressure is too high to try to make up for it, slinging the paint on the surface.
Make sure you are