Target Coatings, Inc.

[Jeff Weiss]

Prep & Jonathan
What are your filter set-ups on your equipment? Are you using a pickup filter at the fluid stinger tube that sits inside the fluid container? DO you have screens in your gun fluid passage area? Are you using tip screens?

There is no right/wrong answer here- however, I have found that certain filter locations can cause unusual film formation effects with WB finishes, especially if they have been exposed to solvent-based finishes prior to the changeover.

Give me your replies and set-ups. I'd like to drill into this.

JW
_________________
Innovation Driven By Vision

[jonathanmahnken]

Here is my screen set up Jeff.

1. Rock catcher on pick up tube
2. Extra fine screen on hose inlett (dont know what # the mesh is, but do know i cant get one any finer.)
3. extra fine screen at gun handle

No tip screen.
I too was thinking that it almost looked like errant particles of dried finish. I nee to get a good magnifying glass.

[jonathanmahnken]

Prep let us know if the 313 tip helps??? Also do you see the cratering on the first coat? I seem to only get it on the second coat. Have not gone for a third coat yet.

[moreprep]

Hi Jeff,

I get the cratering on the first coat, over a latex enamel underbody primer, which is
over BIN (I like the holdout and wetting properties of Sherwin Williams Premium
primer relative to BIN) which has been sanded with Norton 220 yellow
sandpaper (presumably with stearates). I wiped with DNA and a microfiber cloth.
The wood is poplar, which I milled on an M&M moulder (predecessor of
Williams and Hussey).

The photos are of the first and only coat of EM6500 beyond primer.

My screens:

1. Pretty fine 1" diam disc screen at the bottom of the cone filter which feeds the
pump (I made a hopper out of a new automotive oil funnel and copper pipe,
so I could shoot a quart at a time, no priming needed). About 60 mesh.

2. Graco Nova approx 1" x 6" cylinder screen filter on pump output (under the black
knob in left front of the pump). This is a 60 mesh screen.

3. 100 Mesh filter at gun inlet -- this is a Binks special filter that is about 3/8" diam.
by 1/2" long cylindrical, made of stainless steel, with vertical slits. This filter is much
smaller than the usual 1/4" diam x ~4" airless gun filter.

Here are some other details:

A. I used acid core flux to solder the copper pipe, but I ran a lot of water through
the pipe under pressure afterward, not connected to the pump.

B. The pump piston assy. had been replaced and was not used before my use.
There was some small amount of paint residue in the pump outlet filter housing.
I don't know if it's oil based.

C. I used Titan pump oil on the piston shaft.

D. I used Titan pump anitfreeze to store the pump between uses.

If it isn't an impurity problem, it's interesting to consider the effect of the nozzle
on the paint. Shearing? Turbulence that creates transient concentration
gradients, which are then transported to the surface? Some potential for
mischief there.

I'm facing deadlines, so I'm grateful for your help. Maybe I could try the 210 FF
airless tip, but that would take at least 2-3 hours...and I know I don't want to
go that route.

[jonathanmahnken]

Your sand paper is not the problem. I have used norton quite a bit with targets products. Do you have a .013 tip for your aaa gun?? From what it sounds like your screen setup is more coarse than mine, so maby tip size is the culprit.

[moreprep]

Jonathan,

Sorry, let me correct that. The only sample that was the first coat over primer
is the picture rail on the left in the bottom left photo. The others had a previous
coat of EM6500 over primer, which was then sanded with 220. The craters
were present in all samples. On the picture rail where this was the first coat
of EM6500, they seemed to heal mostly during drying. On the other cases where
this was the second coat, the craters remained.

I don't have a tip screen, just a 100 Mesh filter at the gun inlet.

Also, I guess I only have a 210 fine finish regular airless tip, but I got so much
overspray when priming, I'm not eager to go back to it. Also some clogs. I was
advised that 0.011 is the smallest you want to go, to avoid clogs.

-"More Prep"

[moreprep]

The model for crater formation suggests the following:

A Mathematical Model for Crater Defect Formation in a Drying Paint Layer
P. L. Evans, L. W. Schwartz,1 and R. V. Roy
Journal of Colloid and Interface Science 227, 191–205 (2000)
doi:10.1006/jcis.2000.6877, available online at http://www.idealibrary.com

1. Craters are caused by a localized concentration of surfactant --
a small blob, say. Crater size depends on the size of the initial
surfactant blob.

2. This creates a strong surface tension gradient, driving the
coating away from the surfactant. This occurs very quickly,
and is opposed by viscosity. There is no time for the paint
to level before the crater forms.

3. The crater dries in, and typically has a raised center and a raised
rim. This is what I'm seeing.

4. The size of craters is insensitive to dry times, but is sensitive
to the rate at which viscosity increases with increasing resin
concentration during drying.

So, viscosity is a knob. I heated the paint to reduce viscosity for
better spraying, but maybe it wants to be colder. We still need to
find out where the contamination is coming from (not air in
Jonathan's case, maybe in mine). It still could be that the airless
nozzle is creating problems. I'd like to know if anyone has sprayed
EM6500 using an airless or AAA without craters.

[jonathanmahnken]

I have tried both hot and cold spraying the 6500 and it doesnt seem to make a difference. the only thing I noticed is that when sprayed really hot the craters will freeze in place more quickly. I also have had this happen with other brands of white wb laquer, and only after the first coat but could solve it by flooding the surface, which doesnt work that well with the 6500. I dont think it is contamination. But if it is I would say that the more likely culprit would be the tint being put into it by the paint stores, possibly not completely agreeing with the chemistry of the 6500, and after being atomised, whatever the tint is disolved in, breaks apart from the paint and lands back on the surface with the paint. I know, a wild theory, but I really dont think it is pump or air contamination, as i have seen similar issues in the past with other brands. I have ordered 5 more gallons, and will be ordering a graco 313 or 14 double orifice fine finish flat tip to see if this helps. It is odd though how the problem does not occur whe sprayed through my hvlp.

[moreprep]

I had a dirty sprayer, with excess oil in the packings, which was
passing through the hose and probably caused the cratering I
was seeing.

I removed the gun, and ran water through the sprayer, aimed
at a bucket lid. I could see oil coming out and floating on top
of the water. That would probably explain the craters.

My sprayer was in fact full of old, dried oil based paint. The pump
cylinder and piston were new and clean, but filter chamber
was lined with old paint, and the hose connecting the pump
to the filter chamber was dirty as well. I disassembled and
stripped out all the old paint from all wetted parts (and dry parts
as well) using water based stripper. This took considerable time,
and is not for the faint of heart. The sprayer is as clean as new now.

After I did this, I ran 5 gallons of water through, two gallons
mineral spirits, then 5 gallons water, then 2 gallons DNA, then
more water. Guess what -- I was still seeing either oil or mineral
spirits coming out of the hose along with the water. So, I took
apart the pump, and there was still mineral spirits in the lower ball
area, despite the 5 gallons of water having passed by. There
was also a lot of oil around the packings. It turns out that the
pump rebuild instructions say to soak the leather packings
in SAE-30 motor oil for an hour before installing. Since my
pump was freshly rebuilt, there was still excess motor oil coming out
of the packings. I cleaned this off, and greased the piston and
packings with Mobil synthetic automotive bearing grease
(hopefully no silicone in it), which is waterproof. Then I reassembled
the pump and very lightly oiled the piston with Titan pump oil.

Finally, no more obvious oil coming out of the hose!

If you don't have dried paint in your filter chamber, and no other
obvious problems, and are experiencing cratering with your airless
pump, I suggest taking the pump apart and cleaning the packings
(about 30 mins). There may also be residual mineral spirits
in the pump.

I'll post the results after testing in a few days. I believe this is
the source of the cratering I was seeing.

[moreprep]

Continuing to talk to myself...

All of the samples I showed in the above photos dried with
tiny micro-cracks, every 1/8" or so. The cracks are eye-shaped,
and can only be easily seen with a magnifying glass. The cracks
appear to penetrate the full depth of the coating.

The samples were coated at about 72 F and
allowed to dry at a temperature of about 60 F, after abotu 30 minutes
at 72 F.

There could be some oil in the coating as I described, but I would think
it would cause the craters, rather than tiny cracks.

What is the likely cause? Air entrapment?

As the coating dried, I did notice some irridescence with my LED
flashlight, which may have been microbubbles. I have read
that microbubbles are a common problem with waterborne
coatings applied through AAA. There are no bubbles in the
dried coating, just cracks and the aforementioned craters.

[jonathanmahnken]

Sorry, should have posted this on friday night, but didnt have time. I went and bought a cheap 313 flat tip to see if tip size would make a difference. And it did. I wasnt able to eliminate all of the cratering but this is a big improvement. I am now thinking that if I go to a 314 fine finish double orifice tip the problem will be pretty much solved. I know what your talking about with the cracking and bubbling, which in my case is due to applying the product too thick in that area. We will see if I can get all the bugs worked out with a new 314 ff tip. I have done several flushes in my rig since I last posted so I am almost reandy to rule out contamination completely.

[moreprep]

Hi Jonathan,

I noticed that oil and thinner remained in the pump lower ball area, even after
many gallons of water flushed through. You can very easily remove the lower
ball assembly (designed this way to allow easy cleaning of the ball). You might
want to check it.

I started out with a 0.015 tip in my Binks AA-4000, but it glopped on far too
much paint too quickly, even at low pressure. So the upper limit on tip size
is probably less than 0.015".

While talking with various coating and equipment reps, I heard repeatedly that
one has to go up to a 0.013" tip to avoid microbubbles with pigmented waterbornes.

It is possible that I applied the coating too heavily, causing the cracking, but the
cracking is uniform. I did get full coverage in one coat. I applied enough to get
good leveling.

I'm leaving open the possibility that EM6500 is a finicky coating. I'm trying
other brands of pigmented white lacquer to find out now. I have noticed
that a little bit of water goes a long way in reducing viscosity with these coatings.
Also, some brands have viscosities that are relatively insensitive to temperature
in the range of interest, so there are some differences.

[jonathanmahnken]

I did pull my lower ball assembly and cleaned it. Only thing I got out of it was some dried finish that had probably been there a while. Full coverage on the first coat is alot to ask of a waterborne I think. I am taking mine in two steps as I am using 6500 as my primer and color coat. firts coat light but even, then I sand and do one more even coat to get full color strength and a nice smooth surface, which I am able to do with a cheap flat tip, hoping that a fine finish 313 or 314 will be the solution. If you are not priming first you might consider doing it in two coats.

[moreprep]

Thanks...

I did apply it over primer, and also over one previous coat of em6500, sanded.
I'll report results from a mil gauge on my next trial. I think I was in about
the 3-5 mil range, but that's only an estimate.

One question -- do you apply light coats that are thin enough not to flow out,
leaving a sort of dusting on the surface? I've heard of using a "wash coat" first,
which helps avoid sag on vertical surfaces, but I haven't had the courage to try
it, for fear of not getting the leveling that this "lacquer" is so good at....

Does em6500 "melt in" on successive coats, as is claimed for em6000?

[jonathanmahnken]

3-5 mil is definitely on the thick side. I shoot a coat that is just thick enough to be evenly wet. I try to stay around 2-3 mils as best I can. the wash coat is not necessary. However my first coat is always on bare wood and it soaks in for the most part. Yes it does melt into itself like the 6000. I find that I really dont have to apply it super wet to get it to flow out. you will be surprised at how well it flows into itself with just a nice wet pass. Give it time. after about an hour it should be tight and smooth. I just picked up a graco 414 ( they didnt have a 314)double orifice flat tip today and will be trying it tomorrow. I will keep you informed on the results.