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Author Topic: Dope Blushing  (Read 1635 times)

Offline Balsa Butcher

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Dope Blushing
« on: February 26, 2009, 09:15:25 AM »
Just sprayed Sig Lite Coat on my latest project.  Major blushing.  discovered that the main reason was not the outside humidity but that I hadn't  drained/vented my compressor in awhile and it was contaminated with water so the humidity came from within rather than the elements...Bummer.  A search on this forum indicated a few more coats with clear plus retarder ought to remedy it.  Any other suggestions other than a complete re-spray?, (no time for that with VSC in 3 weeks) Thanks in advance.  8) 
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Pete Cunha
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Offline Serge_Krauss

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Re: Dope Blushing
« Reply #1 on: February 26, 2009, 09:35:38 AM »
Just spray some thinner into the air near, but above the blushed areas, so that it can settle gently on them. Take care though that you don't induce a warp by softening the dope on one side vs. the other (you could do both, if this is a possibility). This has always worked for me. It does get the moisture out better, since you are not covering it up with more dope. You get the benefits without the wait and further delay.

SK
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Offline Mark Scarborough

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Re: Dope Blushing
« Reply #2 on: February 26, 2009, 10:30:27 AM »
use SLOW drying reducer,,
Oh and drain the tank on your compressor,, keep the airline off the floor while your spraying,, and drain the airline too before you spray. n~
did I mention to drain the tank on the compressor? HB~> ask me how I know,, one body shop I worked at installed a  500 gallon air tank for that specific reason, to let the air cool and condense,, worked great,, until we forgot one month to drain the tank, there was like 5 gallons of moisture in there! yechhhh,,
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Offline Allan Perret

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Re: Dope Blushing
« Reply #3 on: February 26, 2009, 12:23:14 PM »
As I understand it, blushing is caused by the water vapor being trapped in surface.  Was wondering if a light heat application with a hair dryer would help.   Not questioning that the thinner mist works,  but dont understand how that gets the moisture out.
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Allan Perret
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Offline Mark Scarborough

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Re: Dope Blushing
« Reply #4 on: February 26, 2009, 01:01:25 PM »
It opens the surface of the laquer up allowing the moisture to evacuate ( hopefully) remembering that laquer can be redissolved with thinner unlike a catalyzed product
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For years the rat race had me going around in circles, Now I do it for fun!
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Offline Balsa Butcher

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Re: Dope Blushing
« Reply #5 on: February 26, 2009, 01:10:49 PM »
Thanks all, I'll give it a try...when the sun comes out again.  And yup, I know better but really blew it regarding the air tank...Dohhh  HB~>
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Pete Cunha
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Offline Clint Ormosen

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Re: Dope Blushing
« Reply #6 on: February 27, 2009, 06:46:13 PM »
OK Pete, it was sunny today. How'd it go?

The Playboy turned a nice shade of green today.
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Offline Balsa Butcher

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Re: Dope Blushing
« Reply #7 on: February 27, 2009, 06:59:46 PM »
Well, upon close application and an application of thinner I think it may be a case of the color (primarily light blue) applied too lightly.  Prior to the clear coat the color looked nice and even but after after the clear was applied the undercoat (white) seems to have bled through in certain areas.  Due to time constraints I'm going to live with it, maybe I'll get extra points for an authentic "weathered" look as that is what it resembles.  8)
« Last Edit: February 28, 2009, 08:48:51 AM by Pete Cunha »
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Pete Cunha
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Offline Bob Reeves

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Re: Dope Blushing
« Reply #8 on: February 28, 2009, 10:13:39 AM »
Couple days ago I squirted Sky Blue on my new ship, was very suprized how well it DIDN"T cover over Polar Gray.. This morning I touched up a few thin places I knew were not getting any trim.. This was a Brodak light blue which from what I understand has more pigment than SIG.. Guess we both learned something about light blue..
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Offline Allan Perret

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Re: Dope Blushing
« Reply #9 on: March 08, 2009, 06:07:21 AM »
Quote from: Mark Scarborough on February 26, 2009, 10:30:27 AM
use SLOW drying reducer,,


You guys always preach to not substitute other brands of thinner,  stick with one brand / product line through out.  So if he's spraying Sig Litecoat there is only one thinner available,  he doesnt have slow, med, fast choices like you do with professional auto product lines.   
I also have blushing issues (live in southern Louisiana) when spraying dope.   When humidity is high (like most of the time around here) where does main contribution of the moisture that causes the blushing come from.  Is it from the compressed air coming out the gun or from the water vapor in the surrounding airspace.  What would be more effective,  de-humidifier in shop or air drier in air line feeding the gun? 
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Allan Perret
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Offline Balsa Butcher

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Re: Dope Blushing
« Reply #10 on: March 08, 2009, 09:45:45 AM »
The dope I applied after draining the air compressor reservoir did not blush so I think water contamination was the primary culprit.  I also suspect that insufficient color coats were applied originally so that when the clear was applied the already thin pigment diluted further and caused the base coat to show through  in places. 

The happy ending is that I lightly sanded the blushed parts down, reversed masked and re-sprayed most of the faded area.  The final result was much better although there are still areas where blushing(?) can be noticed. FWIW, Sig thinner was used throughout, dope finishes are sure getting pricey! A pic will be posted in the classic forum.  8)
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Pete Cunha
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Offline Pinecone

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Re: Dope Blushing
« Reply #11 on: March 12, 2009, 01:42:10 PM »
There is a product designed to dry the air when spraying.  It lookss like a 4 - 5" long piece of overly large hose.  Inside is silica dessicant.  I got mine from the company I bought my DeVilbiss HVLP guns.  They also sell airbruses.

You still need to drain teh tank and use a moisture serarator.

This guy: http://www.tcpglobal.com/spraygundepot/itemdetail.aspx?itemno=DEV+130502

They also have larger capacity wall mounted regulator dessicant seups.  Also good prices on spray guns.
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Terry Carraway
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Offline Allan Perret

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Re: Dope Blushing
« Reply #12 on: March 23, 2009, 05:23:57 PM »
Quote from: Serge_Krauss on February 26, 2009, 09:35:38 AM
Just spray some thinner into the air near, but above the blushed areas, so that it can settle gently on them. Take care though that you don't induce a warp by softening the dope on one side vs. the other (you could do both, if this is a possibility). This has always worked for me. It does get the moisture out better, since you are not covering it up with more dope. You get the benefits without the wait and further delay.

SK
To use this method, do you have to wait for a lower humidy day to do it, or will it work if you do it in the same humidity that cause the blushing in the first place?
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Allan Perret
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Slidell, Louisiana

Offline Serge_Krauss

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Re: Dope Blushing
« Reply #13 on: March 24, 2009, 10:38:51 AM »
Allan-

I think that it should work in high humidity as well as low. Extreme humidity?? Hmmm - I doubt that it would cause humidity to repenetrate the dope. It shouldn't hurt to try.

I have generally used it in medium humidity. The last time, the blush did come from moisture in a friend's tank, and I fixed it at home in my basement. This was in early spring with probably 60% humidity.

SK
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Offline L0U CRANE

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Re: Dope Blushing
« Reply #14 on: March 24, 2009, 05:44:08 PM »
Allan,

The problem is a bit more than heating is likely to reach. Dope skins over fairly quickly, so any moisture dissolved into the thinner (reducer?) is likely to be trapped in for a long time. Misting thinner over the surface softens that skin, and helps allow trapped moisture to meet the atmosphere and go 'way.

BTW, dope takes a LONG time to cure. I've cut into models doped years before, and the smell of dope and thinners is usually still very evident. ...And our CL models almost always have small vent pathways to pushrod holes or leadouts, etc.
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\BEST\LOU

Offline Ralph Wenzel (d)

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Re: Dope Blushing
« Reply #15 on: March 25, 2009, 07:39:29 PM »
Can't help with your current problem, Pete, but next time, don't embarrass the dope and maybe it won't blush!  S?P

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Ralph Wenzel
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Offline Balsa Butcher

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Re: Dope Blushing
« Reply #16 on: March 26, 2009, 08:32:36 AM »
Yup, gotta admit it...sometimes my paint jobs are a bit of an embarassment...but this one was actually pretty good! 8)
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Pete Cunha
Sacramento CA.
AMA 57499

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