Here is a post I did sometime back for someone wanting to know about
spraying latex. It should have some pertinent information for you.
I just finished spraying a bunch of passage doors this weekend. A very long
I have a Graco, 4-stage turbine HVLP with a 2 quart remote pot. Since latex
is thick, I figured I needed a big tip to get the necessary flow, so I
dropped $90 for a #6 (2.5 mm) set which calls for 26+ seconds on a Ford #4
viscosity cup. That is the biggest tip made for this equipment. I already
have the #2 - #5 tips.
In hindsight, I then called Graco after buying the tip and talked to tech.
Boy, did I get a lesson in spraying latex. I told him I had a #6 tip and
would he please give me some guidelines on spraying latex. The first thing
he said, was that he didn't think the #6 tip would work. Although with the
remote pot, I could turn up the pressure and get a good flow, the turbine
wouldn't be able to push enough air to atomize it. He was right and there
went $90 down the tube. He suggested thinning the latex 10% and adding
Floetrol. More thinning can change the sheen and bonding characteristics.
Then start with a smaller tip. If I can atomize before I reach full air
flow, then go to the next larger tip. When I get to a tip that won't
atomize at full air flow, go back to the smaller tip. He said I would just
have to live with the smaller output and subsequent slower coverage (it
equated to a lot of time). I thinned the latex about 12% and added 8 ounces
of Floetrol per quart of latex. That is the maximum Floetrol that
supposedly won't change the sheen of semi-gloss or satin (I used satin), or
change the color. Too much starts adding a yellow tint to the paint. I
ended up with a #4 tip with a #3 air cap. The #4 tip is 1.8 mm. I went
down to the #3 air cap because it is a higher velocity air flow for
atomizing and does atomize a little better than the #4 air cap (this is a
hint in the manual). It doesn't make sense because the viscosity suggested
for the #4 is 20 to 26 seconds with the #4 Ford cup and the latex is so
thick it would take minutes to empty the viscosity cup. I had already asked
him about that earlier. He said that although the #6 calls for around 26
seconds, it could actually spray paints with viscosities up to 160 seconds.
Also, all the tips can spray at much thicker viscosities that are listed in
the manual. Although it will spray at higher viscosities, you must use a
slower fluid flow so there is enough pressure to the air cap to atomize it.
The viscosities suggested for each tip size is the optimal viscosity range
for that tip; but it isn't the limit of viscosities that can be sprayed for
each tip. Again, he was right. I could get good atomization, but I could
only move the spray gun about 1 foot every 4 seconds or so. It took about
8-9 minutes for each door side. The material did have some orange peel and
it splattered some as it went down, but with the Floetrol, it leveled out as
it dried and I got a really smooth surface. I put it on pretty thick, so I
could have easily gotten by with one topcoat, but I opted for two.
I do find that I can spray oil base paints to a really smooth finish much
easier than latex with about 15% mineral spirits and 15% Penetrol. The
sheen and adhesion don't seem to be affected. I use a #4 tip for that, too.
From the finishing newsgroup at Woodweb
(http://www.woodweb.com/cgi-bin/forums/finishing.pl you might pose your
question there), I get the idea that a conversion HVLP spray gun will handle
heavier viscosities better than a turbine HVLP. I guess that is because you
can get more atomizing pressure. For the conversion guns, it seems the
consensus is Asturo or Kremlin. But be prepared to drop $400-$500 for the
gun alone. However, with the conversion gun, your "spray rig" isn't very
portable with a big compressor.
Obviously, for latex, the airless is still the way to go, but it is not very
good in the shop for finishing cabinets and furniture.
BTW, I wouldn't even try to spray latex with less than a 4-stage turbine.
It would take too much thinning or a way bunch of time.
Hope this helps,
Anyone here use a HVLA (high volume llw pressure) spray system to apply
latex-primer/paint on thier painted projects?
i'm building a fireplace mantel w/ MDF and pine and was hoping to build it
all up, then spray it with primer and eventually white paint (latex).