First spray painting results - yuk!

[philf]

The attached photos show my first efforts at sparay painting, and I was using a new Earlex HVLP starter kit. The timber was plywood,

Hi Jillb,

This is a snip from a thread at rec.woodworking, thread below might interest you, it's about spraying shellac but the snip from thread below by Robert or nailshooter41 gives good info in spray setup. Go to thread below for the entire thread, hope its of some help.

Rgds,
Phil.

PS sorry for long post

spraying shellac (Ping Nailshooter) - rec.woodworking | Google Groups


<and if="" you="" have="" the="">Hi, Joe.
I am of two minds on this, so I will split this up. First, spraying
shellac isn't hard. Read everything Karl said, as there is good
advice there.

To amplify his post a bit, spraying with an HVLP unit can be done.
But for me, I have found that I like it even thinner than Karl. I
like to thin it to just about water, work fast, and make multiple
coats. I get it down to about 1# or so and go from there. The beauty
of shellac is that one coat melts into the next, so there is no
disaster from bad coat like you get from varnish or poly.

So thin away, and DO NOT try to "hang" a coat. Spray quickly, and get
the surface evenly wet, with coats at a thin 2 mil or so. (For
reference, that's thinner than a paper dollar).

I thin shellac that much for two reasons. First being that I can
recoat in 30 minutes with no problems. So coat buildup is not really
an issue. Thin coats don't sag as long as you keep moving, and they
are easy to control.

Here is a tip I found on my own when spraying thinned finishes: spray
distilled water out of your gun onto a smooth surface like an brown
cardboard box. It is easy to see how your flow out will go, how fast
to move, and how to adjust your gun. It is good at mimicking the
first coat on sanded wood, too.

Next, mix up some finish and spray it onto a cardboard box that has a
smooth vinyl finish on it that protects a graphic, like a microwave
box, or any other box with a shiny finish. The shiny box will tell
all as to your spray ability.

OK, the second reason. Flying in the face of reason, shellac sprays
out better when thin, it dries more evenly, doesn't tend to blush, and
actually has a better pot life in the sprayer. It has something to do
with the amount of resin-to-solvent formula, and there is so little
resin in the overall thinned spray that it tends to NOT be as sticky
as a thicker cut, making it much to manage when spraying. It
shouldn't work that way, but it does. I spray enough material for me
to think the surface looks wet, then I move on.

The only downside I could see, is that using shellac in this manner
means multiple coats. But at 1/2 hour or so to recoat, you could get
all you needed in a base coat in just an hour and a half. If it's
just a seal coat, then a couple of coats will do it.

A word on HVLP spraying of any thinned finish. These of course are
generalities, but they work surprisingly well.

First, if it is drying before making contact, you are probably using
too much pressure, the wrong tip, both, or you are positioning the gun
too far from the surface. Start with the tip (actually, an aircap)
that approximates a 1.3 or 1.4mm tip.

Turn down the pressure, and let the small droplets come out, don't
think "spray". Let it sprinkle out, then turn up the pressure just
enough to come close to an atomized spray, but not quite. On your
four stage, it takes much less pressure than you think, and with
thinned material you may be blasting it to bits if you see it drying,
or a powder on the edges of your spray pattern.

Make sure you are the correct amount of distance from your target
surface. To get the correct amount of space, cut yourself a small
piece of something 8" and use that as a start point. Depending on the
material i am spraying, I have the gun as close as 6", and as far away
as ten. But they are all designed with 8" as their maximized
performance distance from the surface.

It is VERY easy to wander back an inch or three, <
pressure turned up to high, the bounce back will make you think you
need to move the gun back from the surface.>>

This is very important. Don't move the gun back. And if you do,
NEVER more than 10". If you have seen the way the spray pattern
develops from a gun after it leaves the tip, you will understand how
it takes the proper distance to develop a good spray pattern of the
droplets. The HVLP systems are easy to use if you understand the
mechanics behind them, and you must pay attention to them. Correct
droplet patterns don't develop under 6", and they degrade after 10".

So if you are getting plenty of material on the surface and there is
bounce back or drying powder, turn down the pressure. If that doesn't
work, close down the pattern a bit as well.

The last thoughts on shellac. Find yourself another can for your gun
and fill it about half way with your alcohol thinner. After you shoot
a coat, take the can off with the shellac in it, and seal it someway
(I use a piece of cardboard with something heavy on it) and put the
alcohol filled can on the gun. Shoot out a couple of ounces until you
get a fine watery spray, as shellac can be bad about clogging the ways
and tips. I hate spitting guns or poor patterns.

So, if you are still there, (I know, ask this guy what time it is and
he will tell you how to build a damn clock!) I have a question for
you.

Why would you use shellac on a gaming table? If you are thinking it
is some kind of superior bonding agent, it can be, but if you are
using NEW or very clean wood, there is no need for it. If you are
using it as sanding sealer and intend to sand to smooth the surfaces,
I get it. But as a sealer, there probably isn't a reason to do it.

Almost nothing in the finishing world sticks to itself like the same
finish. Whenever you can, avoid dissimilar finishes. If your wood is
dirty, possibly contaminated with chemicals, is reclaimed wood, or you
are refinishing, shellac is a splendid choice. It makes a great
bonding platform to build your finishes on since it will cover a
multitude of bad things that will foul your finish.

If you are going over this with poly, store your shellac and start
spraying your poly. No primer needed.

Something important to remember, especially on a hard use piece such
as a gaming table. The top coat will only be as good as the
substrate. Actually this is a hard, fast rule in all of painting and
finishing.

But in point, that means that the top coat will be softer than it
could be as the bottom coat (shellac) is soft and more flexible than a
poly or varnish used as a top coat. (These are kissing cousins -
don't fear the poly on a gaming table). A softer more flexible
substrate means less wear resistance on the top coat.

Worse, if one of your poker buddies dents the table somewhere and you
clean it up with a mild water based cleaner, you can cause blush or
discoloration due to shellac's poor water resistance. (Imagine the
shoe/boot wear on the base!) Now amp up your water based cleaner with
a good detergent base like 409, and you can LITERALLY peel the finish
off after a few good cleanings.

So if you have new, clean wood that has been carefully prepared, your
top coat should be your prime coat as well. Just put on the amount
indicated by the manufacturer for each coat, and follow the times set
out in the MSDS sheet.

Good luck on your project. Hope this helps.

Robert
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[Dengue]

Many thanks for all this information, philf, it certainly is a lot to absorb, but I value the experience you have passed on from Robert, and will be applying it