Air Bubbles Forming in Paint

[Brian Massey]

I had what I thought were paint spatters in the finish of my wing. I sanded and found that the dope had bubbled. When I sanded the bubbles off, the undercoat was exposed in perfect little dots. After respraying, "they" have formed again, in the same spots. It would appear to be bubbles formed by air pushing through the wing after it is sprayed. This is on the 1/16th sheeting of the leading edge which has a total of about 8 coats of dope.

The wing is completely masked, with no openings, and I'm wondering if in the heat of the sun (I'm spraying outdoors) the air expanded and pushed through. I'll resand and do it again being careful not to put the plane in direct sun, and then move it indoors as soon as I spray.

Any thoughts, ideas or suggestions will be welcome.

Brian

[RC Storick]

This could be one of 2 things. One is contamination or two the thinners is too hot and causing the outer layer of paint to scab over too quick trapping air. It has to escape some where.

[Brian Massey]

By "too hot", do you mean to much/not enougth thinner? I'm spraying Randolph's dope thinned with their thinner and using their retarder. It has only done this on one spot on the wing, and it has done it twice on that same spot. It's a little cooler today, so I'll try again.

Thanks,

Brian

[RC Storick]

By "too hot", do you mean to much/not enougth thinner? I'm spraying Reynolds dope thinned with their thinner and using their retarder. It has only done this on one spot on the wing, and it has done it twice on that same spot. It's a little cooler today, so I'll try again.

Thanks,

Brian

By hot I mean to fast drying. So with what you have said I would look at contamination

[W.D. Roland]

I have had this happen several times in the past and these are as best ideas the old noggin could figure.

A car left out in primer over night: pine tree pollen collected on primer. NOTHING would remove it and only thinned the pollen and let it penetrate deeper into the primer. Sanding did same and also mostly smeared it.
Decided to paint anyway and it bubbled.

8ft span wing using polyester resin to seal grain. 1st coat was old resin and had spots that did not cure 'hard'
usually a second coat of good resin will make first cure. Not this time!
Did not cause problems until after painting. apparently the uncured resin continues to 'gas'
Have left it in a window van for 2 summers. will try to sand and paint again one day.

WD-40 or similar sprayed on something in the vicinity of primer is absorbed into primer. Bug spray, solvents.....

Have also as had heat cause it like described above. paint inside and move into sun and air in balsa expands and pushes through.
Have cured this problem by letting surface to be painted sit in sun to get get hot, then paint and move to cool place after paint 'flashes off'

I suspect your primer is contaminated......what ever you try will only push it further into primer and then into the wood.

An idea on what to do if it happens again.
Knock the top of bubbles of with sand paper and with thin superglue on a tooth pick to put enough super glue to
coat 'spot'  the resand , prep , paint and drink lots of beer.
The beer is so you leave the airplane alone while it dries!
Good luck and let us know what happens.

David

[Brian Massey]

drink lots of beer. The beer is so you leave the airplane alone while it dries!
Good luck and let us know what happens.

David

This part I think I can do. 
Brian

[Allan Perret]

Looks like contamination, clean surface using naptha and /or windex.  Dont touch any surface after you have cleaned it before spraying.   How much thinner and retarder are you using?

[Claudio Chacon]

I had the same problem not so long ago while painting a field box with acrylic lacquer under the sunlight in the summer. I sanded the thing two hours later, let it dry for 24 hours and repainted it, but this time in the shadow.
Problem solved.
Let me suggest not to paint under the sunlight again, specially a wing.

Good luck,
Claudio.

[Brian Massey]

Looks like contamination, clean surface using naptha and /or windex.  Dont touch any surface after you have cleaned.   How much thinner and retarder are you using?

The Randolph's B-dope is thinned by about 60% with a mixture of about 75% thinner and 25% retarder. (It seems to spray and flow well enough.)

This morning I wet sanded with 600 grit and reshot; no bubbles but now there are little shallow spots where the bubbles were. I'll re-sand tomorrow with 300 grit and reshoot, hoping to fill in the holes.

Thanks,

Brian

[Howard Rush]

Could it have been water droplets from condensation in your system? 

[Randy Powell]

I'm with Howard. Looks like water in your airline.

[Brian Massey]

I have the giz in line that's supposed to remove any moisture (do they really work?). Since it's only on that one section of one wing, I'm led to believe (by some of the posts here) that some sort of contamination is to blame. 

I'm no "20 point" builder by any stretch of the imagination, so I look at these experiences as something to learn from. 

Sadly, my new TT will not be perfect. (As if anyone expected that.)

Brian

[Gary Anderson]

HEY!!!WHAT YOU TALKING ABOUT? I think you do a great job on your planes and that's the end of the subject!!!!
In a week or two you'll have grass stains on her anyway??? (Let Mikey fly her for ya???)
See ya tomorrow.

Gary

[sleepy gomez]

Though the problem could be moisture most likely there is a different problem.  It is called fish eye by pro painters.  It can be caused by several things but most likely it is the surface being sprayed or brushed which has picked up some wax or similar from cleaning or even sanding.  The cause is some, even slight,  wax  on the surface.  This cannot be sanded off.  It cannot be washed off. 
      Now, go to the local paint store and ask for some FISH EYE ELIMINATOR.  It comes in a small bottle and is inexpensive.  A few drops in the your paint is all that is needed.  This will cure the problem.  I have used fish eye eliminator for forty years.  I still recall the first time I needed it and the torture I went through before I found the answer.   SLEEPY

[W.D. Roland]

Brian
All will be good as now that the Doc's allow no mo Beer for me there is now plenty for all( ie. I no longer cause beer shortages)

few other thoughts.
Like Howard said could be water but that is usually wide spread. I have had days when the humidity was high and other variables right to cause condensation a discharge end of things.

The dryer filter at the gun end of the hose needs to be new at the beginning of each project.
Old air hoses can be a problem, microscopic rubber particles.

Use a dryer separator at the compressor. those with a drain at the bottom can be cracked open to constantly bleed water while spraying.

If your compressor is in an air conditioned room make it as cold(dry ) as possible.
Drain the tank 4 or so times while making this 'dry as possible' air. 


After blowing up you picture large enough I see you are actually having balloons not just a lifting bump.
I also see depressions where the paint is being sucked into the surface? Something is gassing, expanding and then contracting.

Is there filler in affected area? water based?

From my memory and the brands of paint I worked with(RM) your retarder amount seems high.

Fish eye seem to be something more like a total failure of surface tension of the wet paint and make a crater that resembles a miniature meteorite crater in side view X section.

Brian
your post #8 indicates it might be time for the superglue trick and or sealer primer in affected area.
Although at this point you may have the problem 'bridged' and only need to level surface and spray LIGHT coats.
This may lead to low gloss/rough finish that needs fine wet sand and compounding. Hand rubbing compound is getting hard to find but still around. Don't bother with machine compound unless you can get a buffer to it!
The machine stuff is good for canopy clean and polish followed with plastic polish/wax.

Or sand all off and start over

As you can tell I have mucho experience at screwing up paint jobs


this link with painting trouble shooting chart might help.
http://www.autobodybrands.com/trblshtg_page.html
 more
http://www.paintscratch.com/problems.htm

http://www.monokote.com/lustrekote/painting-tips/topr7200tip5.html

If all else fails supply every one at contest with lots of free beer and no one will notice the problem.
Well except for me.

David