Stewart Systems - tiny bubbles

Greetings,
I am spraying Stewart Systems silver metalic with a HVLP gun. The paint looks beautiful when I hang the gun up, but when I come back in a couple of hours, tiny bubbles have appeared in the surface. After it cures the surface feels like it has sand on the surface. Not good! If I sand the surface there is a very tiny hole where each bubble had been. If I recoat, the same thing happens again. I see lots of complimentary posts about Stewart Systems - has anyone else had this problem? What am I doing wrong? What is the solution?

Thanks much,
Don Owens

Lots of factors to consider. Here's a few.

You might try to cut the problem apart to determine the cause by working with test panels. In other words, is the material and/or the spray technique producing the bubbles or is the way you prepared the surface causing eruptions and bubbles?

Are you CERTAIN there is no water (humidity) or oil (from the compressor) in the air line?

Are you following the temperature & mixture guidelines for the paint?

Are you using a brand of reducer or hardener that's from a different vendor than the paint supplier?

Are you supposed to SEAL the primer before topcoat?

Silver metallic is one of the hardest colors to shoot. It will look good in the booth but terrible in the sun when all of the tiger stripes appears so take a completed panel outside and determine if there are more problems than just bubbles.

When I shoot any metallic I get the best results with base coat / clear coat. After the final coat of base, I open the fan and fog the entire surface changing directions constantly. That levels the paint so it's consistent and even and lays a lot of metal on the surface for the WOW effect. When dry, I tack cloth, then shoot the clear.

Here's a nice example of a high metallic ruby red using the aforementioned fog technique and an hvlp gun.

Rubly red

That is beautiful paint work - Would you like to paint my airplane?

Thanks for the detailed suggestions. I think I covered all that - $100 filter, all products from Stewart Systems, etc. I suspect my "spray technique" might be to blame as others post good things about the Stewart Systems, water borne paint. Their support has been great, by the way. I would like to hear from others who have used this product.

Thanks,
Don Owens

Don,

Did you mix the paint too vigorously, getting air bubbles in the paint? Stewart cautions against getting bubbles in the paint, stirring, not shaking.

Stirred not shaken

Richard,

Good thought. I did stir it with a stir-stick - no shaking. The paint goes on and looks beautiful until about one to two hours later and then the tiny bubbles begin to appear. So, I don't think I am introducing the bubbles by stirring.

Thanks for the idea,
Don Owens

Flash time is another factor to consider

springcanyon said:

That is beautiful paint work - Would you like to paint my airplane? Don Owens

Click to expand...

Thanks for the compliment. It took us three weeks to paint the 9A. When the 6A is ready, I will shoot the fuse on a rotisserie so the bottom looks as good as the top instead of working upside down. Like the 9A, the wings will be mounted on a jig that permits them to be rotated so the surface is always flat to the painter. That minimizes sag and allows the painter to "see" the flow as it rolls out. We may use hi metallic base coat / clear for the divisible parts such as the wing tips for accent.

Try shooting one medium cost on a test panel that's been cleaned with acid etch & prep before shooting (assuming those chemicals are compatible with the paint). If you're still getting bubbles, you can eliminate the prep work to the surface as the cause. My guess is "solvent pop" but with water based paint, where are the solvents?

Here are some excerpts from Sherwin Williams on "bubbles" that may prove helpful:

Liquid solvent (thinners/reducers) becomes "trapped" in the paint film when the surface layer skins over too quickly, preventing their evaporation into the atmosphere. Solvents that vaporize within the paint film leave bubbles, pinholes or craters as they push through and "pop" the surface. Solvents can be trapped due to:

1. Thinner/reducer evaporating too fast for spraying conditions;
2. Inadequate flash time between coats;
3. Excessive film thickness or "piling on" of heavy/wet coats;
4. Too much air movement causing surface to "skin over" before solvents evaporate;
5. Excessive purge/flash time before force drying.

Painting is difficult so I feel your pain. The first car I painted (a 57 Chev) I used the roof as my experiment because it was mostly flat and divisible from the rest of the car. I "shot" it 11 times, messed it up 11 times, sanded it off 11 times, until I finally figured out the right combo of pressure, volume and technique. Everything has to be perfect to get quality work so keep practicing on throw away items until you get it right and determine the problem.

Tiny bubbles

Thanks again, Barry, for the information. I think you are on the right track. I believe in the case of the water borne paint the water IS the solvent, so one of the 5 possibilities you mentioned may be the culprit.

Anyway, I am going to load up my horizontal stabilizer on friday and take it to Stewart Systems' shop for an analysis by the expert - Dan. We will sand the top coat off (second time), reprime, and apply a fresh top coat of metalic silver. Hopefully he will solve the problem.

I'll post the results next week. Maybe it will help someone else that is using the Stewart Systems paint.

Thanks,
Don Owens

I sprayed some Stewart's White Primer today on some of the removable panels on my -7 interior. Here's what I found. If the surface isn't completely dry , little bubbles come up. Also if the coat is too thick, bubbles appear.

A dry surface, light coat of paint and distilled water vs. tap water. Much better.

Hope this helps.

Darren

tiny bubbles

I apologize for taking so long to get back to this. Stewart Systems couldn't give me a positive reason for the tiny bubbles, but I think I have figured it out. It seems that I wasn't waiting long enough between coats to allow the undercoats to properly "tack up," or "out-gas." I now check the time precisely between coats and also do a touch test before applying the next coat - especially the fourth one. This seems to have eliminated the bubble problem.

Do not, do not, use any kind of paper cup for mixing paint or water. A silicone emulsion is used in the manufacturing process. This is guaranteed to cause "fisheyes." Don't ask me how I know.

I don't know if it is directly related, but I am doing a Super Cub build (for hire) and am using the Stewart process. It is the first time I have used their products. I ran into major problems with the Ekofill, with tiny bubbles appearing after spray applications. It looked and felt almost like sandpaper grit. After working with Stewart, they sent me an additive for the primer that eliminated the problem 100%. According to Dan, they are going to include this component in all of the primer automatically.

FYI, I use a Croix (Graco) HVLP turbine system. You have to use the 1.0 mm tip to get good results. 1.2 may be acceptable, but 1.4 will not work. I do not thin the primer at all, just strain into the cup and spray.

Good luck.

Tom