Microbubbles

[AllanD]

I would like anyone's ideas on this problem. I am spraying cabinets with SW Kem Aqua Plus which I have done many times in the past with excellent results. This time I am getting many tiny bubbles, some pop and leave a tiny crater so they are definitely bubbles not detritus. It happened yesterday with the Kem Aqua surfacer which I solved today with a very light sanding with worn 220. I initially blamed the product because I had just ran to the Monroe SW to buy some as I was out of stock. They had put the can in the shaker before I got there so I thought that might be the problem. However, I just applied the topcoat (low gloss white) and it it doing the same thing just not quite as bad. I have had that can for a while and it was only stirred. Here are the other details:

Done in my spray/finishing room with powerful exhaust. The air comes through my refrigerated dryer.
Devilbiss Finishline FLG4. I think it was a 1.3 tip
My on gun regulator bit the dust so I went this morning and got a new one. Running between 19 and 20 at the gun.
I dialed the volume back so as to get a thinner film. It helped some but still some bubbles.

I read that SW recommends using Butyl Cellosolve as a retarder, thinner if this happens but I would like to avoid that if possible. I also read it is not the safest chemical. However, I do use a supplied air respirator. Thanks.

 

[bainin]

Not familiar with the Kem Aqua Plus, but in my world when using thicker fluids that have some viscosity to them, a vacuum degas chamber did wonders for getting rid of
unwanted bubble formation during cure.

b

 

[AllanD]

That's interesting Bainin. Kem Aqua is a spray only paint so it is pretty thin plus the gallon can of paint was never shaken. So when you place the container of paint in the vacuum chamber how long do you generally leave it? I have a vacuum pump I use for air conditioning work so it wouldn't be much trouble to make a chamber.

 

[FredP]

Martinis are shaken not stirred. Wood finishes not so much. The bubbles should dissipate over time in the can. I would buy a new can for the immediate use and save the other for the future. Oh and, Don't let them shake it. Slowly stir. I learned this with epoxy the hard way of course.

 

[Gotcha6]

Would it be possible to use an additive such as Floetrol, designed to smooth out brush marks?

 

[AllanD]

I think so Dennis. I was debating on adding some alcohol to thin it but Floetrol or propylene glycol would probably be better in that it would also slow the drying. I wouldn't have known they shook the primer except I heard the manager tell her assistant that the can I came to get was in the shaker.

The top coat came out quite a bit better. I just made another observation though. The face frames and the drawer faces are solid soft maple and they basically did not have any bubbles. The 3/4 maple plywood I used for this set of cabinets I got from a hardwood dealer and it weighs much less than I am used to. A 4x8 weighs 42 lbs. and I think what we usually use weighed around 70 lbs. The veneer looks fine but the inner cores are very porous and light. I wonder if it is air coming out even through the layers of primer.

 

[Westpacx3]

In my world it's called solvent pop. The finish product be skinning over before the solve can escape. I add an inhibitor to keep the finish open longer. Odds are they changed the formula or you went too thick too fast. I have issues with it at times and not at other times. It's odd. Sometimes it is also a contaminate that did not get cleaned off the surface.

 

[Gofor]

I am not familiar with the coating you ae using.

That said, micro-bubbles are usually caused by two things:
1. High humidity, resulting in the atomizing air causing tiny water droplets to form and are combined into the spray. With this being a water soluble coating, I doubt this would be the problem.
2. Contamination in the air supply. This could be water or oil. If you have an oil/water separator or filter on your air supply, it may not be coming from the compressor. However, you said you are using a new gun. There could have been machining oil residue in the gun's air passages. When I get a new gun. I disassemble it and submerge it in solvent or DNA, and then blow out all the passages, both fluid and air. Using a water-based coating, I would suggest DNA to fully clean it with.

Butyl Cellosolve can greatly extend the tack and drying time, depending on the amount, so be careful if using it. It can greatly increase the likelyhood of runs and sags.

 

[bainin]

It depends on the air content/viscosity of the materials involved. If you can pump down to a couple hundred milliTorr , bubbles will be produced. One note-if the material is chock full of air, quite a bit of expansion happens and can bubble out of your container and make a mess. Its good to have a chamber you can see into to watch for this and its good to have a vent valve on your line to use as a bubble popper while pumping ( a quick opening/closing of the vent while pumping destabilizes the bubbles and collapses the expansion) Plan accordingly

As its a spray system, you may unfortunately be putting a lot of air back in during the aerosolizing/spray process.

b

 

[AllanD]

I've actually had this FLG4 gun for several years. Now that I mostly used water based products it is by far the most used of my guns. I still think it is interesting that for the most part the bubbles only formed on the plywood, not the solid maple. I do plan on using the left over paint (I'm too frugal not to) on future jobs so I will try to get a hold of some of the retarder.

 

[Willemjm]

The carrier, water and air in this case is being trapped under the final film, before it can evaporate.

R6K 25 as a retarder may help a little.

With WB finishes the age of the product and the amount of pigment added will greatly affect this.

On raw plywood, with the fist coat sometimes this is almost unavoidable, however after sanding the now sealed surface will show a big improvement with the subsequent coat.

The FLG 4 is not the ideal gun for this coating. What may help is changing the tip from 1.3 to 2.2, Then keep the coat as thin as possible, while maintaining a wet coat the gun about 6” away from the surface, wide open and move the gun really fast.

FWIW, I have been down this road many times.

 

[AllanD]

Thanks Willem. I have the 2.2 tip so I can try that next time. I typically would have been worried about it producing too heavy a coat and getting drips. I move the 1.3 fairly fast I thought. I guess I could dial back the needle in that case. You are right about the raw plywood, the topcoat was definitely better.
I searched for R6K 25 but came up empty. Does it go by any other name?

 

[Willemjm]

Thanks Willem. I have the 2.2 tip so I can try that next time. I typically would have been worried about it producing too heavy a coat and getting drips. I move the 1.3 fairly fast I thought. I guess I could dial back the needle in that case. You are right about the raw plywood, the topcoat was definitely better.
I searched for R6K 25 but came up empty. Does it go by any other name?

See page 2 under application for the R6K25. The data sheet is attached. I'm not sure how good your local SW outlet is with stocking industrial finishes, we have to order and get it shipped from Charlotte Industrial, as the local branch does not carry all the industrial finishes. It will help a little, but the real issue here is the FLG 4.

To explain a little bit about the 2.2 tip:

The thickness of your coat depends on how fast you move the gun. Slow is a thick coat, fast is a thin coat. You want only so much to get a wet coat.

The FLG 4 blows a huge amount of air and you have a film finish which dries very fast. If you notice, the overspray lands on the floor as dust, with the carrier fully evaporated, because it dries so fast. So what is happening with your 1.3 tip, is the finish film has already started to dry somewhat once it hits the wood, making the water carrier hard to evaporate under the film. That is why you are getting bubbles. So in short, with that spray gun you want to get the finish on the surface as fast as you possibly can, by using high volume of product coming out of the gun and moving the gun fast. It takes some practice, but give it a shot.

Dialing the pressure down on your gun will also help.

 

[Oka]

Agree with some others, Humidity, Contamination (on surface, in the gun or caused by disruption in the environment) and/or/plus gun/tip settings. Al could be part or all of the cause. I have sprayed this material, never had an issue...... the one time I got over spray on my wife's plants.......well I told her it was a plant improvement

 

[Dee2]

Agree with some others, Humidity, Contamination (on surface, in the gun or caused by disruption in the environment) and/or/plus gun/tip settings. Al could be part or all of the cause. I have sprayed this material, never had an issue...... the one time I got over spray on my wife's plants.......well I told her it was a plant improvement

Next time try green paint!

 

[AllanD]

Thought I would update this thread. Couple weeks ago I needed to spray some drawer fronts of soft maple with the white Ken Aqua Plus. I debated on using another spray gun like my Devilbiss Technica which I generally just use for very thin solvent based auto paint or to stay with the FLG but change to the 2.2 tip and lay a thick coat. On reading more on the product I decided to stay with the same FLG and 1.3 tip but turn the air down. I had been using around 20 to 22 psi at the handle which is what the tip calls for. I tried it at 11 psi at the handle and did not have those problems with bubbles and cratering even on a piece of plywood I included just to test. So thanks Willem you were correct that it was too much air.

One of the confusing things that day was that since it is a water based product I figured the very high humidity on the day I had problems should have slowed the evaporation and made the bubble problem less likely.