Ahhh... rainy days and a mug of coffee. I originally wrote this in
response to David in an earlier thread asking for some help on
finishing with waterborne. But it turned into a lengthy tome with the
unexpected rain and all my appts. for work and estimates being
With that in mind, I thought I would start a new thread so that
everyone hear can chime in with their own experiences.
David - I wrote a response to your last lengthy dissertation to help
as much as possible, but it got lost in cyberspace somewhere.
Probably someone on the bbq or sheepshearing newsgroup is screeching
to me right now about using OT in the header. Since you seem up
against it, here is another shot at it.
No one can help you get this to 100% guaranteed solution without being
there with you. All advice (certainly mine included) about what is
going on is based on personal experience and your description of the
problems coupled with you attempts to resolve them yourself. So as
they say, YMMV. I use solvent based finishes by choice due to their
predictability in application (at least in my hands), the results they
give, and my familiarity with that type of finish. I use water borne
when required, all the principals are the same as solvent, and I know
the products you are using are top shelf. So is your application
I don't know how long you have been doing finish work, and don't know
how familiar you are with turbine powered HVLP. If you are an old
high pressure sprayer, good HVLP requires a brand new skill set, one
that comes only with experimentation and practice, practice,
practice. I don't know if you are doing this professionally, part
time, finishing this at your own home (with the a/c climatizing the
house and affecting humidity greatly), or on a remodel job (a/c
working intermittently doing humidity voodoo dance) or on a jobsite
that is has the a/c heater turned off completely.
All that being said, I would start by doing this: buy two gallons of
your finish and the recommended thinner for it. Call MLC and ask them
for the MSDS sheet on this product. It usually has all the safety
info on it, but many also have recommended application protocols.
These are good place to start.
For water borne, I use distilled water as a thinner, never bothered
with flow agents. My 4 stage (and your 3 stage) have plenty of power
to push the material out of the gun. Buy a good set of stainless
steel measuring spoons and download the measurement conversion tables
on the net so that you will know that 1 tsp = 15 ml. Go to the
builder recycling thrift store or a lumberyard and buy a piece of 1/8
(or whatever is cheap - door skins will work) plywood. Take it home
and clean it up and sand it. This is your test bed. When evaluating
or learning about a product, I usually take 2" masking tape and tape
off squares 12" high and 2' across. You need the two feet across so
you can mimic your spray motion, so don't go 12" X 12". If you test
on both sides, sand one of them off.
Mix up 1/2 quarts at a time of finish, and write down your mixes, and
spray your plywood in a clean, dry place. Observe the results. Make
your notes. Adjust the pressure on your gun, vary your mixes, add the
flow enhancer and leave it out. This must be done on a stable weather
day as you will learn nothing if it is 55 degrees in the morning and
75 in the afternoon with light showers.
You may not get it done with just a couple of gallons. But I can't
put enough emphasis on you taking this to the woodshed. You just need
to get in there and hammer this out. I have said this a million
times, finishing is like any other tool, you have to learn how to do
it. That means an investment in time and money. The finish I am
using now in my Fuji took me about a month to get all the way up to
speed, and I burned about $350 of material learning to use it. But
now... confidence in the material and application no matter what the
weather is doing or the jobsite conditions, is high.
Thoughts on the finish: First, call MLC. Tell them what you are
doing and what is happening. Personally, from your description I
think you are needing to thin more, but that may be incorrect in this
case. As them what the MAX amount of thinner you can put into the
sealer would be, and then go from there.
That leads to the turbine gun itself. If you have the three stage,
you probably have the adjustable rpm model. Put this to the highest
rpm, and epoxy the knob in that place. The Turbinaire gun is a very
nice gun, I have used them and they were my second favorite to use.
But that gun that comes in the 3 stage package has been around for a
long time (several years), and was designed to be used with a high
volume output turbine. It was NOT made for someone to turn down and
adjust volume flow. You can restrict the flow with the valve, but
that doesn't restrict the amount of air available to the gun. When
you restrict the output of the turbine, you take away the available
amount of air to the gun.
Why is this differnce important? You HVLP not only pushes the air at
the aircap to atomize the material, but it siphons off 5 lbs of
pressure to pressurize the paint pot on the gun. Less available air
to gun means less immediate pressure to the pot when you pull the
trigger. Inconsistencies in pressure mean inconsitent finishes. I
was really suspicious when I saw the variable speed turbine, and
didn't know why it was made or how it was supposed to work. But a
call to a completely honest Turbinaire distributor confirmed
everything I just wrote. Results? Keep the knob all the way over
unless you are spraying tanning juice on your girlfriend.
Your pressure at the valve or on the gun should be turned down quite
low. With HVLP you are NOT atomizing the finish. If you are getting
anything remotely close to traditional high pressure overspray you
need to cut down the flow at the gun. You should be spraying droplets
with your gun like a gentle mist. I have literally sprayed clear onto
front doors in garages where I just put down a 9X12 dropcloth and
didn't have ovespray problems. When you are practicing on your
plywood, turn the gun (again at the valve) down until it just
sputters. Now open the valve the gun 1/4 turn at a time, until you
can just get the finish out in a clear fine mist with droplets of
consistent size. If you start to get a lot of bounce back from the
surface (remember... 8" from the surface) you need to cut back the
pressure and thin your material. If the bounce back comes back to the
gun (probably anything more than about 4 inches) the pressure is up to
too high. Thin.
I am suspecting that your bubbles are the results of too much MLC flow
material, not enough thinning, and the pressure too high. This is the
practice part you need adjust your gun to the MLC material.
Two other things contribute to bubbles. Incorrect mixing technique
and incorrect application thickness. If you pour all your stuff into
the sealer and stir it vigorously you will introduce bubbles. Since
HVLP does not blast the finish apart then redirect it with air, it
will allow some find bubbles to stay in the sealer when exiting the
gun. In the good old days of high pressure, I was more worried about
solids on the bottom of the cans of finish (paint), so I would add the
thinner at the paint store and have them SHAKE the damn can up. Since
your HP equipment blasted the finish anyway, it took care of the
bubbles. Now with you should add your thinners/retarders/hardeners
and mix slowly for a long time. I mix with a clean stir stick.
The other thing that will cause bubbles is to have the pressure a
little too high, and put on the finish too thick. You are getting
closer if most of your bubbles are working themselves out. Going
beyond how the bubbles got in the finsh (spray pressure too high or
improper mixing) the bubbles get trapped because the finish is
starting to catalyse where exposed to air. The finish "skins over",
not allowing the bubbles to escape. If the finish is too thick, it
cannot outgas the solvent before it skins over, so everything is
screwed up. Bubbles are trapped, witness lines become apparent, and
varying degrees of gloss are seen. When the finish catalyses it has
to follow its own precise formula of not curing too much on the top
before the project side is well into the same process. The bubbles in
your finish that you see disappear are actually the result of the
contraction of the finish (when the solvents are leaving) squeezing
out the bubbles. So in order for that squeeze to take place, you have
to keep the top surface wet as long as needed. See above for practice
When the finish is applied, is important to follow the manufacturer's
recommedations so that you can have a good starting point before
developing your own formulas. I >think< that the recommended
thickness of coat for the MLC product is 3 mil. If you don't have a
gauge, go to the auto paint store and get one as they will really help
when you are trying to see the correct appearance of your coat when
To the last point. If you are doing this professionally, you will
starve to death if you don't master the "off the gun" finish.
Polishing and rubbing out have to be done on occasion, but more often
than not that kind of finish is simply not called for. So that puts
you into competition with the guys that will spray and walk out.
To get the finish to look right, I apply as many coats as needed to
seal the wood. For my favorite finish, I apply three - four coats of
finish, and when fully cured it shrinks down to about 3 mil. I sand
lightly to remove anything I don't like. I never sand between coats
unless I have screwed something up. It doesn't matter what kind of
finish I am putting on.. I never do. On the last coat before top
coat, I very lightly sand with 220. If you sand one part, be
committed to sanding it all for the same appearance of gloss.
Get the correct gloss from the manufacturer. Don't try to knock down
gloss to satin with steel wool, oils, waxes etc. Remember, you aren't
For the final finish coat, I thin as much as I can get away with
(sometimes as much as 50%) and spray a water thin coat over the sanded
and cleaned finish to top coat it. This will provide the proper sheen
for the finish and as thin as it is will dry rapidly helping to
prevent dust contamination.
Good luck. Let us know how you are doing.