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  • August 02, 2021, 06:36:16 AM

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Author Topic: Sig Clear turns gray  (Read 710 times)

Offline Greg L Bahrman

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Sig Clear turns gray
« on: July 05, 2021, 06:48:53 PM »
So Cal 85 degrees. Sprayed Clear coat on my finished plane with Sig 1/2 thinner and Sig 1/2 clear. Clear turned gray or fogged really bad and this is with Sig retarder. It looks terrible. Is there a fix. Tried spraying with retarder and thinner and also with just thinner to no avail. Is this the brand or the operator. News said humidity was 35 percent. Kind of looks like the passed six months have gone down the drain. Yuk. Appreciate any help. Do I need to buy a humidity gauge and when is the best time to spray ?
Greg Bahrman, AMA 312522
Simi Valley, Ca.

Offline Jim Svitko

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Re: Sig Clear turns gray
« Reply #1 on: July 05, 2021, 07:48:22 PM »
When you say it turned "gray" or "foggy", are you referring to blushing?   The dope evaporates fast, and, even with retarder at times, it is not enough to slow the drying time to prevent blushing.  And, too much retarder is not good.

I have never heard of Sig dope, or any other dope, "graying", so I am wondering if there is moisture somewhere that is getting in the mix and you are getting blushing.

Normally, blushing occurs in higher humidity conditions but humidity is not the only factor.  Humidity of 35% sure seems low enough but you also have to consider the dew point.  If the dew point is high enough, you will get blushing since the cooling of the surface due to dope evaporation will lower the surface temperature to the dew point and the moisture will condense and be trapped.

Keep an eye on dew point as well as humidity.  When the dew point is 60 or higher, I do not spray dope.

 

Offline Greg L Bahrman

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Re: Sig Clear turns gray
« Reply #2 on: July 05, 2021, 08:14:17 PM »
I did not have any blushing problems spraying colors.....I had this same problem on another plane I was spraying black, only the clear blushed.
I have a moisture filter on the compressor and on the spray gun.
Greg Bahrman, AMA 312522
Simi Valley, Ca.

Offline Dave Hull

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Re: Sig Clear turns gray
« Reply #3 on: July 06, 2021, 01:05:03 AM »
Greg,

Sorry to hear you are having paint woes. I seem to have my fair share, too. (Five thumbs to hold a spray gun and my own cloud of "pet" gnats, for starters....)

The variables described are all related--they are not independent. Relative humidity (RH), air temperature (assume this is dry bulb temperature), and dew point temperature. So for your estimated conditions of 85F air temp and 35%RH you would have an approximate dew point of 56F or so. So you were perhaps slightly below Jim's rule of thumb limit on spraying.

I think we also need to consider the different climates that different guys are coming from. July up in the valley (any of the valleys around Los Angeles) is likely to be hot and potentially very low humidity (RH)--once any morning fog has burned off. I'm kind of suspecting that East Coast and gulf summer weather has a whole different trend...having suffered thru some 90/90 weather there myself. We might hit 105F pretty routinely, but like the joke goes, it's a dry heat....

Dave

Offline Jim Svitko

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Re: Sig Clear turns gray
« Reply #4 on: July 06, 2021, 03:14:34 AM »
Although you could have blushing, even at 35% humidity if the dew point was high enough, I think Ty's experience is what probably happened to you, as I also had a similar experience.

On one plane many years ago, I noticed that the white looked somewhat yellow, or "dull", after spraying clear.  I used a gray primer.  If, at that time, I tried to get the clear on in less than ideal atmospheric conditions, I most likely used too much retarder.

Retarder is a slower drying thinner.  If too much is used, it can work its way down into the dope layers, softening them and then you have problems.  Another factor is how heavy the clear coats were that you applied.  If you had a high retarder content, then too heavy an application could cause problems.

The total amount of retarder should be as little as necessary to prevent blushing.  The Randolph dope guide says that the total retarder content should not be more than 20% of the total thinner content.

Let's say you are going to mix a total of 8 ounces of clear dope/thinner mix and you want a 50/50 final mix.  If you go by the Randolph guide, you will mix four ounces of unthinned clear with 3.2 ounces of thinner and 0.8 ounce of retarder.

If atmospheric conditions are good enough, you should not need any retarder at all.  If you do use any then use as little as possible.

Offline Greg L Bahrman

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Re: Sig Clear turns gray
« Reply #5 on: July 06, 2021, 11:53:12 AM »
I don't understand it, the plane sat in this warm weather for 3 days before the clear was applied, but it appears you are correct in that the primer is seeping thru the paint. It's apparently not the standard blushing of the clear but the primer seeping thru the paint. I don't know how to fix it other than sanding the paint off the whole ship, which is not going to happen. I'd rather jump up and down on the plane in the driveway and put it in the trash. It had the potential to be a nice looking plane but things have transpired to the point of my sanity being questioned. Any suggestions to make sure this doesn't happen again? Can the primer be sealed before color is added? This is just to much work to ruin it with this problem. Thanks all.
« Last Edit: July 06, 2021, 12:45:11 PM by Greg L Bahrman »
Greg Bahrman, AMA 312522
Simi Valley, Ca.

Offline Jim Svitko

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Re: Sig Clear turns gray
« Reply #6 on: July 06, 2021, 03:46:31 PM »
Greg, do you remember the clear mix that you used?  That is, how much retarder did you put in there?  If you went beyond the Randolph percentage, then you need to use less retarder next time.

Another thing you can try is to use a lighter shade of gray for a primer.  The Polar Gray from Brodak is too dark for me.  I lighten it by mixing the Polar Gray with Insignia White.  Or, get some white primer and forget about the gray.

Dope takes quite a while to really set up.  On the surface, it appears dry.  But down deep, it has not gassed off enough and is susceptible to what happened to you.  I heard 30 days might do it.  Even if you waited that long, go easy on the retarder.

I see no easy way to fix this other than sanding off all the dope and starting over.


Offline Greg L Bahrman

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Re: Sig Clear turns gray
« Reply #7 on: July 07, 2021, 08:06:44 PM »
The gray that's bleeding thru the red is not primer. It's the Sig gray blocking coat I sprayed a couple of days before spraying the colors.
Greg Bahrman, AMA 312522
Simi Valley, Ca.

Online Tom Luciano

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Re: Sig Clear turns gray
« Reply #8 on: July 08, 2021, 09:21:00 AM »
Avoid wet coats when applying topcoats. Especially when using retarder. I learned the hardway when doing my crossfire.  I kept blowing thru the white paint because i was painting it like a car and trying to lay on a shine. The shine comes later in the sanding and buffing. Caveat to that is dont apply too dry or adhesion problems could arise if not using enough thinner.

Best of luck
Tom
AMA 13001

Offline Jim Svitko

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Re: Sig Clear turns gray
« Reply #9 on: July 09, 2021, 08:12:27 AM »
Greg, are you not seeing any of this problem on the white areas?  Only the red?

Some colors are best applied over a base of white or pale gray.  I once applied orange over the Polar Gray.  Although the orange looked OK, it lacked the brilliance I was looking for.

Colors that appear opaque will still allow a darker underlying color to bleed thru.  This might be part of your problem.  Red might look opaque but darker colors under it will tend to bleed thru, thus dulling and darkening the final appearance.


Offline Alan Resinger

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Re: Sig Clear turns gray
« Reply #10 on: July 09, 2021, 12:03:07 PM »
Greg, you mentioned using retarder.  Was that used in the initial clear coating? If the humidity was only 35%, you shouldn't need retarder.  Any time retarder is used it shouldn't be any more than 10% of the total reducer/thinner used. 
Red colors of dooe are notorious for poor covrage.  White is best as an undrcoat for red or a mix of white and polar grey which l call white grey.  Six parts white and one part grey. 
Take a close-up of the red area where the dark is showing tnrough the red. The pics are a bit to far away to really show the problem clearly.  To fix the problem from what l can tell is going to require either a total resanding or adding on a lot of paint and with a big increase in weight.

Offline Greg L Bahrman

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Re: Sig Clear turns gray
« Reply #11 on: July 12, 2021, 01:38:20 AM »
There was only a couple of small spots where the gray showed thru the white. The first coats of clear were applied 1 to 1 thinner/clear, no retarder. The gray showed thru almost immediately. I did put it on wet. I used retarder in the second coat of clear with the hopes that I could save it but it was to late the damage was done. The wing doesn't look to bad so I've started sanding the fuse. I am a sport flyer so I'm not worried about it being perfect. I was just curious as to what I did wrong. Thank you for all your input. I'll use all your suggestions on my next ship.   y1
Greg Bahrman, AMA 312522
Simi Valley, Ca.

Offline Dave Royer

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Re: Sig Clear turns gray
« Reply #12 on: July 12, 2021, 09:44:56 AM »
I've had your problem when it was actually the white that had blushed. The subsequent clear coat eliminated the blush and revealed the gray block coat beneath. It was on the bottom so I lazily just left it that way.

Offline Alan Resinger

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Re: Sig Clear turns gray
« Reply #13 on: July 13, 2021, 08:14:35 PM »
Dave, thanks for the heads-up, l will remember to look at the bottom next time l appearace judge your model.😁😁😁

Offline Dave Royer

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Re: Sig Clear turns gray
« Reply #14 on: July 13, 2021, 10:41:32 PM »
Sorry to disappoint you Alan but that particular airplane will not be seen at any contests.


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