Air-Assisted Airless settings for waterbornes to reduce Micro Bubbles

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I've read the post from about a year ago with everyone weighing in on the reasons for micro bubbles in waterborne finishes, however it seemed like there were so many different opinions on why it's happening. I've been struggling with this for a long time, and am wondering if anyone has figured-out a trick yet? I'm using a Kremlin 10.14 pump with a MVX gun and spraying with a 09.112 tip with the pre-atomization port. The paint and finishes spray out and lay down nice, but then after a few minutes these bubbles start to form. Will pump settings, temperature, or a whole different finish manufacturer fix the problem?

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Dave Edgerton

[X] View Member Profile Name: Dave Edgerton Company: Fine Edge Cabinetry and Millwork Location: Canada Member's Business Categories: Architectural Millwork - Custom Millwork Cabinets - Kitchen & Bath Cabinets Member

Hi tom
We need to now what you are spraying before your question can be answered.

Tom

Member

Oh sorry, I have had this problem with "General Finishes Clear Poly", and "General Finishes Milk Paint".

Dave Edgerton

[X] View Member Profile Name: Dave Edgerton Company: Fine Edge Cabinetry and Millwork Location: Canada Member's Business Categories: Architectural Millwork - Custom Millwork Cabinets - Kitchen & Bath Cabinets Member

Ok that answers everything. GF clear ploy is the worst lacquer to spray through a kremlin. I have had this problem since we switched 2 years ago and after getting the same results we have switched to ICA for our clear coats. The GF pigmented sprays fine, it is the clears that are absolute s--t with a kremlin. To solve your problem, switch to another waterborne clear. Been there, done that. I even called GF and they told me that my equipment was outdated.

Jeff-1

I am by no means a water base guru but it's my understanding that the pump itself is at least as important, if not more important that the pressure setting and tip sizes.

You need a pump that has a big fluid chamber to keep from shearing the fluid in the pumping operation, which as I understand it, is the main cause of micro bubbles.

The Kremlin 10:14 pump has a pretty small fluid chamber compared with many larger pumps so you may want to look into a bigger, more heavy duty rig.

Or you can just go old school and use a pressure pot for your water based spraying, that's what I do.

Denny J

It appears to me that you are spraying the paint too thick. I have been spraying GF products or years and they are excellent products.

Can you post your finish schedule? If the door was primed and sanded smooth you should get a glass smooth finish. If this was the sealer coat, then increase the air and back the gun away from the surface while moving your hand faster. That particular problem is caused by the mil thickness being too great and the finish is skinning before the flash off is done.

In my experience the best way to get rid of the micro bubbles is to move your gun farther away from the surface you are spraying.

Dave Edgerton

[X] View Member Profile Name: Dave Edgerton Company: Fine Edge Cabinetry and Millwork Location: Canada Member's Business Categories: Architectural Millwork - Custom Millwork Cabinets - Kitchen & Bath Cabinets Member

Denny-J are you spraying the gf with a kremlin? The issue is the compatibility of the pump with the product. While GF works fine with a pressure pot it is terribly sensitive to shearing in a kremlin

Denny J

I spray it with either a CAT AAA or a Graco Merkur AAA depending on if it is tinted or clear and they both work.

I am just saying that even if I sprayed it with one of my cup guns with a PPS it would look like that as well. Waterbornes are not designed to spray to the Mil thickness that solvents are and for those who make the transition this is one of the things that gives the most problems.

To test if I am wrong, sand that door in the picture with a sanding sponge until it is smooth and then spray a coat of GF poly over it at about 4 mil wet and see what happens.

Another problem that occurs with paneled doors is that to get even coverage of the frame and panel, several passes are made and the film thickness on the panel next to the frame gets too thick and you get that effect seen in the picture.

Jeff-1

Denny J is correct about WB finishes liking a thinner application coat than solvent born, they dry much faster and generally give you less headaches all around when applied at a lower wet mil thickness.
But runs, finish cracking and poor drying are usually the biggest problems associated with too much wet film build.
Personally I've never seen micro bubbles that I could definitely chalk up solely to too many wet mils.

Tom

Will heating the fluid help reduce the shearing at all? Or maybe adding a extender to allow it to flow out a little better? I also get a lot of build up on the tip of the gun, any ideas on how to fix that? I'm assuming that's related more to the pressure settings than the fluid.

Dave Edgerton

[X] View Member Profile Name: Dave Edgerton Company: Fine Edge Cabinetry and Millwork Location: Canada Member's Business Categories: Architectural Millwork - Custom Millwork Cabinets - Kitchen & Bath Cabinets Member

Tom thats exactly what happens with the GF product at the tip, It does not happen with any other waterborne we have used. Just have to keep some solvent handy with a toothbrush to clear it off every now and then.

Denny J

Every WB I have sprayed will do that at the tip. It gets worse if the seals are bad and don't allow the fluid to shut off the way it should.

Jeff-1

Another option in sort of the opposite direction than a bigger AAA pump is a diaphragm pump, which basically takes the place of a pressure pot and allows you to spray at lower pressures with conventional or HVLP guns.
Generally less expensive than AAA too.

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