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 as close to that 8" as possible when testing.
Even an inch makes a difference one way or another, and the actual
sweet spot for my Fuji is about 8 - 9".
Finally, if all else fails, check this out:
http://www.spraytechsys.com/literatu...P_training.pdf
It is one of the most comprehensive, intelligent discussions of
practical HVLP use I have ever seen. Good stuff. And while the cap/
orifice tables won't be the same for your fun (such as size 4, or size
3, etc.) since they put the actual orifice size on one of their
charts, you can call Graco and they will tell you the equivalent.
Let me know if any of this helps.
Robert