On May 12, 3:25 pm, "
wrote:
On May 12, 12:20 pm, wrote:

Thanks Robert, A lot of good info in your post. The directions on the can do in fact state a 1:1 mixture. Thinking that might be the problem I cut back to 3/4:1 with the same result. I would guess the thinner
I'm using is ok as I've used the same thinner with success in the past. With both qualalack and parks nitrocellulose.
The can suggests a 35-50# setting. Being an inexpensive sprayer I has
no idea what it is putting out.
My question to you is could the air mixture in an hvlp system have
anything to do with a poor (cracking) finish?
While I've used the sprayer for a few years my experience is limited.
Up until now its been point and pull the trigger.
My guess would be to turn down the air while still maintaining an even flow.
Thanks, Bob

And thanks for responding, Bob. Sometimes you never know if anyone
even bothered to follow the thread they started.

I am setting aside application technique in this as I am figuring if
you have been getting acceptable results with your setup for years,
you have put the time into that aspect of finishing to get it where
you want it.

Turning down the air flow will only make the material droplets bigger,
and give less of a consistent pattern.

New products have to be fine tuned to your equipment with you use
HVLP, and it is much more critical than the old high pressure days.

Here's the easy way to set the gun up with a new finish.
Take a sheet of plywood (anything smooth) outside and lean it up where
you can see the finish in strong light. Turn on the turbine unit or
compressor and set them at a pressure you have had good results with
in the past.

Put some thinned material in the gun and close the fluid control valve
completely. Walk over to the plywood and slowly open the fluid valve
with gun in the proper spraying position. You should see tiny
droplets, no mist. At about 8" from the surface, if you see more than
just a very small amount of bounce back, turn down the pressure to the
gun.

When it covers to a wet consistent surface easily, leave the fluid
nozzle alone. Leave the pressure alone. Check your surface after
your material has dried. On the area that you like the finish, add a
second coat. If it looks good and stays good when dried, you are
finished. I have three HVLP guns that do different things - each has
a little nick in it on the fluid control for the different products I
spray.

Anything is possible, but in this instance, the gun or the air
delivery is not a likely suspect. Unacceptable delivery symptoms
usually attributed to HVLP equipment can be

1) sputter - not enough air to the gun, fluid nozzle opened too high,
product not thinned properly

2) uneven coating thickness - inconsistent delivery of air to the
gun. This can be caused by dirty or blocked air filter, or air flow
set too low

3) A splotch or splatter occasionally on the finish - not enough air
to the equipment to properly disperse the particles (remember, HVLP
doesn't atomize like high pressure)

4) #1, #2 and #3 above can also be caused by a dirty aircap assembly.
Many times when people clean their HVLP systems they don't clean the
holes in the horns, which are a precisely determined set of venturi
that determine direction, pattern and dispersal of fluid droplets. I
clean mine with a wooden toothpick, and the tiny holes with one
bristle from a stainless steel brush

5) Fisheyes, craters and voids - while these are usually associated
with poor surface prep, they can be attributed in some cases to gun
cleaning. Many people use the same gun for both water based and
solvent based products. Water, ammonia, and all kinds of things can
be in the gun from using a water based product. This is classic cross
contamination

Just about everything else happens outside of the gun, leaving only
fluid materials and project preparation.

Cracking or crazing is not usually an application issue. To help bear
this out, if you have been using this piece of equipment for years, I
have to think you have been using it correctly or you would certainly
have run into this before, no matter the manufacturer of sealer.

These annoying problems can be the bane of finishing. They take the
fun out of it. When I am committed (by contract!) to do the
finishing, and something like this cracking pops up, this is how I
keep my head in the game: I ask myself - how much would I pay to get
myself OUT of this mess and finish this project? $20? $30? $50?

Thankfully, for this kind of thing is a $20 science lesson. I change
brands of lacquer ($10 for a quart of off the shelf stuff) and $8 for
a gallon of good thinner.

In your particular case my best guess is the thinner is the culprit.
Behlen's makes a good quality product line, although I am not
personally familiar with qualalac.

Please understand that all lacquer thinners are not completely
compatible with all lacquers. The Crowns, Sunnyvales, etc. are made
from recycled mixtures and may have products in them that react
differently with certain lacquer formulas. Those thinners will fine
with some, not with others. That is the specific reason I use the
above mentioned brands to clean the equipment (hence the term "gun
wash" you have probably heard) but not to mix the products. Sometimes
it just comes down to compatibility.

Since HVLP does not atomize, it is necessary to use products that can
accept thinning well, and aren't too touchy about it. You should know
(and probably do) that ALL manufacturers recommend their own thinners,
retarders, flow controllers, etc., to be used with their product.
This is without exception. But no finishers I know ever do unless it
is economically feasible.

Since you have the Behlen's now, I would try thinning with a really
good quality thinner. If that didn't work, for my own satisfaction I
would change lacquers and try it first with the old thinner, and then
with the new. Unless the lacquer you have is old, a bad batch, or has
been improperly stored (not necessarily by you) or shipped, the answer
should be in there somewhere.

It will be easy enough for you to find out.

Once again, let us know how this pans out. If it were me, I would
spend the dough and get through this as quickly as possible.

Robert

Thanks Robert, Your input is very much appreciated. I think I'll try
different thinner as you recommend. I didn't really think the air was
the problem but I will go through the setup as you recomended just for
peace of mind.
In a way its kind of good that this happened. It got me back on usenet
again.
I used to come to rec craft woodturning daily for years and read every
post. I'm talking way back when google was deja news. Heck I even
remember Arch. Thanks, Bob