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General control line discussion => Open Forum => Topic started by: Michael Massey on August 31, 2009, 10:21:26 PM
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Hi all,
My first attempt at airbrushing a plane was/is somewhat disasterous. I am trying to airbrush clear butyrate over colored butyrate. Both are Randolph. The Thinner is Randolph.
I thinned the dope about 3 or 4 to one. I have my compressor set at about 37 PSI and a moisture filter just before the air brush. The airbrush is a Badger "cheepo" for spraying a larger pattern.
The problem is that I am getting a "fog" when the dope dries. The dope looks wet when it goes on but dries quickly into the "foggy" finish.
Is it drying too quick? Is it too thin? Is it...???????
Any feedback would be great.
Tx.
Mike
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How is the humidity in your paint room? Do you have a line dryer on your paint compressor? What you are describing sounds like "blushing", which is a result of moisture in your paint/air...kinda late now, but do test strips before finishing for real! Sometimes a thinned clearcoat will cover it, but not always
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Sounds like a classic case of blushing. Sickening isin't it?
Blushing
1. Caused by the relative humidity being too high, or the solvents evaporating excessively fast, allowing the temperature of the surface to drop below the dew point of the air, causing moisture to condense on the surface. When spraying a dope finish use one part retarder to three parts thinner to thin the dope to spray consistency. A mixture of one part retarder to two parts thinner can also be sprayed on the surface in a very light mist coat to help eliminate the blush. Don't soak the surface.
Blushing is a condition that occurs when the dope turns white because it is embarrassed that water got trapped in it while it was drying.
Blushing is a temporary condition that goes away with subsequent coats assuming the environment isn't so humid that it causes blushing even when doping dry
Robert
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Michael,
You have the classic case of dope blush. Either wait for a less humid day or add a little retarder (thinner that takes longer to gas off). When adding retarder, never use more than 10% of your total reducer/thinner amount. Also drop your air pressure to 22 - 25%. Susequent coats of dope will cure the areas that are blushed over as it stands.
Alan Resinger
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During my most hassled years at the wind tunnel.....I would often be called to airbrush quickie details such as cockpit windows,logo's detail of various kinds...onto the surfaces of many wind tunnel test models that would still be mounted on the sting or flying mounts..in the test section itself.
Many many times...due to the nature of air compression...(especially in the colder winter months) I would make a habit of WARMING my airbrush paint by keeping them tightly sealed in capped squeeze bottles. I would store these in a larger container of hot water until I needed them.
Worse yet....many of models sported steel wings..fuselages....and after quick masking I then would tent the area and then often would need to give the model a final quick blast of heat from a heat lamp or gun...just before the moment of spraying.
Although a pretty pretty funky-monkey looking set up (that often got a laugh or two from the engineering staff)
However from that time forward.....at least I no longer had to vurrrry' too much about my face blushing or hearing complaints that their purty little windshields and logos blushing or fogging.
The small about time spent in warming the paint paid off. At least this way I didn't have to re-paint and repair my blushed paintings during these high humidity winter daze days.
Also when using paint spray cans....even today on home projects, I still fill a sink basin of water and give the paint cans a quickie warm up before spraying....especially when using fixatives and clear coat top clear coatings on photographs...etc.
Naturally some caution must be used.....(I often got lots of raised eyebrows and poppin eye balls when some of the OSHA-WOAHSA' minded engineering folks would see me grab a heat lamp or a heat gun during those HURRRRRRRY! HURRRY! WAAAAAAY OVER BUDGET WIND TUNNEL PROJECTS. j1 j1 j1 j1 na#
(The little recognition operational aqua-flutter model paint was detailed in Bob's favorite AQUA IMERON color...see hazardous story that almost got me FIRED at Boeing...NOT ONCE, BUT TWICE! LL~
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Just got a couple of E mails...about my drawing in the background of the photo...
Bob Whitman...Boeing's gifted...and legendary ICON flutter model supervisior who retired in 1990.
A million stories about Bob.
(below "depicted Shultzie as a RAT!
I hate to admit...because I was GUILTY AS SIN...when I arrived early one morning and found the THIRD SHIFT CREW... HAND BRUSH PAINTING TOXIC 2 PART CATALIZED IMERON PAIN WITHOUT PROTECTIVE RESPIRATION EQUIPMENT ONTO ALL THE SUPPORT LEGS OF THE STATION 6 WORK BENCHES....in Bob's favorite color AQUA!
that was OK'D by our beloved supervisior Bob Whitman on his 2nd to 3rd shift tie in instruction book!!!
The day supervisior SHUT DOWN THE 2-63 BLDG and called the HAZZZZZZMAT TEAM...who shut down the building...brought in LARGE FANS....OPENED ALL THE WINDOWS AND DOORS.
Everyone in the building was out for the remainer of the day...until the facilities dept could remove all the Imeron painted work tables outside to gas off until the following morning.
Just one of the many times...that I was almost FIRED!!!
After Bob saw my recognition retirement drawing...he grabbed me by the T shirt collar and partly n jest??? Bob started to escort me to the door for--------(the second time!!!)
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I would make a habit of WARMING my airbrush paint by keeping them tightly sealed in capped squeeze bottles. I would store these in a larger container of hot water until I needed them.
Don is right... for some reason the air coming from the airbrush is cooled... I use a Binks Wren, Miller and have used a cheapy Harbor Freight.. with a Binks Compressor or Miller Compressor
my own rules of thumbs..
1. 70-90 degrees
2. humidity is less than 60%
3. Use retarder
4. warm the surface and airbrush (I use shop lights sometimes, but not too close)
5. When painting outside.. here in Washington, I don't paint before 10-11 AM and have had problems after 5 PM
6. If the surface appears "milky" stop and sand the next day carefully.. if he surface is dull, no problems.
7. I don't use an airbrush to apply clear.. just colors and put them on with light coats. It is easy to get carried away.
8. Don't spray too close to the surface, or too far away.. experiment on a practice surface first never spray on the "good" surface without testing first. Old Light Bulbs are great for tests..
9. Clean the surface well. I wash my hands and have used latex gloves.
10. I use Sig Retarder and Dave Brown Plasticizer
(https://www.quicktechhobby.com/Airplane_Accessories/zz1SIGDR001.jpg)
DOPE RETARDER - When Butyrate Dope is used in a high humidity environment, it will sometimes “blush” (meaning it will dry with a dull, milky finish). The best way to prevent blushing is to slow down the rate of drying by using Dope Retarder as a partial substitute for the regular dope thinner. Use only as much retarder as is needed, to prevent blushing, typically 25% to 100% of the normal thinner requirement. Dope Retarder should be used only in the last one or two coats of the finishing process. (I have used it all the way through but don't put 10% in .. 5 % or a little ess has worked for me.. Painting is something you have to learn... and most of us have paid our dues...
(http://www.dbproducts.com/images/product_graphics/flex.gif)
Flex-All
Flex-All is a plasticizer for lacquer, primer, and butyrate dope. In lacquer, it completely eliminates cracking and spiderwebbing. Also it aids in the gloss retention of the paint. When used with dope, it helps reduce shrinking. One bottle is enough for use on several airplanes.
Here are some other suggestions..
Hazing/Blushing
Hazing, associated with lacquers, appears as a cloudiness in the dried clear or pigmented film. This reaction is commonly found with lacquers when relative humidity conditions are high trapping moisture in the dried film.
If hazing develops, mist on a compatible lacquer over the film once the humidity level has decreased. The thinner dissolves the top layer of the lacquer film and allows the moisture to evaporate. The application of too much thinner will result in ruining the finish.
From a ship building site... http://www.modelshipbuilding.com/buildship.htm
If hazing is experienced with Aero Gloss, once the humidity level has decreased, a compatible lacquer thinner should be applied in a fine mist to the dried film. The thinner dissolves the top layer of the lacquer film and allows the moisture to evaporate. This will eliminate the hazy appearance. The application of too much thinner will result in ruining the finish.
When hazing is experienced with Glosscote lacquer, apply mist applications of the Glosscote when the humidity level decreases. The lacquer will dissolve the initial layer of lacquer and allow the moisture to escape.
http://theairbrushforum.com/
http://www.woodweb.com/knowledge_base/Avoiding_Blush.html
"To fix the discoloration, you can fog on a very light application of lacquer retarder or spray another coat of lacquer that has some retarder in it. A general rule for spraying lacquer (or shellac) is don't spray if the relative humidity is above 65%. A more accurate guide is don't spray if the dew point is within 20 degrees of the ambient temperature. For example, if the dew point is 65 degrees and it's 80 degrees in your spray area, don't spray unless you use retarder. You need more than a twenty degree difference between the dew point and temperature to be safe.
As the solvents in lacquer evaporate, they have a cooling effect on the surface they're sprayed on (put a few drops of isopropyl alcohol on the back of your hand to feel the effect). The cooling effect can be as much as twenty degrees. If you cool the surface down below the dew point, water will condense on the surface and you'll get blushing – the milky white look in the lacquer/shellac.
Also make sure the piece you're spraying is the same temperature as the environment where you're spraying. I once made the mistake of taking a piece from an air conditioned space and spraying it in the outdoor heat. The piece was a lot cooler than the outdoor temperature and the finish blushed almost instantly. In order to spray lacquer in high humidity, you'll need to add lacquer retarder. Lacquer retarder is a slowly evaporating solvent (thinner) that lets the moisture escape from the lacquer before it dries. Only use a small amount of lacquer retarder in place of the regular lacquer thinner. Use the same brand of retarder as the lacquer you're spraying and only use as much as the manufacturer recommends. For example, if you usually thin the lacquer 15% with lacquer thinner, and the manufacturer recommends 5% retarder, switch to 10% lacquer thinner and 5% lacquer retarder (15% total thinning as usual). Adding lacquer retarder causes the lacquer to dry more slowly than usual. Spray your coats a little lighter to avoid runs and sags and allow more time between coats."
Here are some fun things to view..
Airbrushing - simple flames - airbrush - learn how to airbrush
http://www.youtube.com/watch?v=tp_IPxJ4POU
Airbrushing Bullet Holes - killer airbrush technique
http://www.youtube.com/watch?v=EKK6X8wDho8
Airbrush Techniques : How to Use an Airbrush, Basic Techniques
http://www.youtube.com/watch?v=RpSqCr8P1Hs
Jim
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Thanks everyone for the very helpful feedback.
I did not think it was that humid but my wife corrected that for me. So...I guess it was more humid than I thought. I did buy some retarder today and will probably give it a shot (pun intended) tomorrow, everything else being equal.
Thanks,
Mike M
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The humidity is probably too high. If you absolutely need to spray the clear on, add a little bit of retarder. And we never use an airbrush anymore than 30psi.
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Thanks to everyone once more.
The Retarder and other suggestions cured the problem. Not only cured the problem, it brought me back from the "brink of disaster." Most all of the "blush" went away and the finish recovered quite well.
Admittedly, the plane was a 40 to 50 year old Ringmaster of my dad's, crashed and "hanger rashed" a number of times, that I did "restore." But it looks pretty good and I plan on using it to try to get other "newbee's" into the world of control line.
Thanks again,
Mike Massey
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Michael,
I often get blushing on my custom guitars because I simply cannot wait for good spraying weather if a client is waiting for their instrument. A couple of tricks you can use to eliminate the blush that has already occured if you don't want to spary more dope/lacquer on the ship.
First, spray a light coat of pure thinner on the spot with the airbrush using a very low pressure and a fairly rapid movement across the area. Then leave it alone for six months or an hour, whichever is the least. (Just kidding about the six months - but allow it plenty of drying time.)
If that doesn't do it, up the pressure just a bit, around 20 pounds for my particular Badger, and repeat using a little heavier coat.
If all else fails, www.stewmac.com sells a lacquer melt by the quarts that will do the job, but USE IT SPARINGLY!!
If you follow the directions on the can very carefully you will find good results. It's expensive if you're only using it for planes, and a quart will last you and your club a lifetime. Mine is only down a quarter and I've used it a lot for around seven years now!
Actually, the thinner trick should handle any problems you have if you go slow and careful. Experiment with it as far as the coats and pressure, etc, and you'll soon sneer at blushing and humidity and all that dope & lacquer misery.
Blessings,
Will