Author Topic: Painting question (Read 949 times)

Robert W · « **on:** February 20, 2008, 05:53:48 AM »

I have been painting a perky with Brodak dope/thinner and have run into something I did not expect. I do clean the spray gun after use with auto store lacquer thinner and this has not caused issues on other projects. The base coat was polar grey and then the top color coat is white. I applied two coats of clear over the white then put on some red trim letters then two more coats of clear. Everything looked good up to this point, then I took some 3M wet or dry 800 grit paper and wet sanded the clear using windex. I cleaned the model with windex and set aside for better weather to spray more clear on. When I went to spray more clear I noticed the model had taken on a nice transperant pinkish/orange color. Note this transperant color is on approximately 70% of the model and located in areas away from the red trim. Everything looked normal until I wetsanded the clear and let it set for a few day. For a test I wet sanded some of the effected area and it appears to be in the clear coat. I do not have a lot of experience and I was wondering if someone has an answer to what I did that could have caused this? I know the fix is to sand it off and start again, but I would really like to avoid this in the future on larger models. Thanks for you thoughts on this topic.

Paul Smith · « **Reply #1 on:** February 20, 2008, 06:02:32 AM »

I'm something of a rookie at spraying, but I've alrady found that simply blowing solvent through the gun dosen't get it done.

When changing colours, I completely tear down the "paint path" and wash every part. I always find trapped paint when I do that.

Robert W · « **Reply #2 on:** February 20, 2008, 06:27:19 AM »

I did not use the same spray gun that I used to shot the red with, I have one spray gun dedicated to clear and used that gun. The color change took place after the clear was sanded and I waited two days to sand the clear. It looked fine even immediately after I sanded on the clear and changed over the course of a couple of days.

Crist Rigotti · « **Reply #3 on:** February 20, 2008, 06:48:30 AM »

I have had similar problems with Brodak dope. That's why I switched back to SIG products. No problems with thier dope.

Randy Powell · « **Reply #4 on:** February 20, 2008, 12:00:23 PM »

Could be a lot of things, I guess. First I'd ask, was the plan sitting in the same room that you shot the red in after you wet sanded it? This sort of thing happened to me once. I shot red trim on a plane then shot some clear over the trim. I was shocked when I came back and all the areas I had shot the clear were slightly tinted red. Fact is, there was red, what, dust I guess in the air from shooting the red trim. I probably should have cleaned the area and the plane before I shot the clear. But the dust stuck to the plane and the clear made is sort of look tinted.

In this case, could be after you sanded and "opened" the surface, dust in the air from the red paint drifted onto it and since the surface had been roughed with sanding, gave some area for the dust to catch. I'd say try cleaning it really well and lightly sand it again and see if the red tint goes away. If not, could be that you got some sort of contamination in the clear you shot.

Robert W · « **Reply #5 on:** February 20, 2008, 04:16:18 PM »

Thank Randy, I will keep your comment in mind for future project. This does sound like something I would do, but I do not believe this is the case here. It had been more then a week before I shot the clear over the red and I cleaned the model surface with windex the night before and a tack rag just before shooting the clear. I also paint just outside the garage door to help keep overspray off of other models stored in the garage.
I did sand an area before leaving for work this morning and the only thing I changed was the sandpaper. The area I sanded appeared to remove the tint until I got home and it is tinted even more now. I am beginning to think it is the windex causing the problem. This does not make a lot of sense because I used the same bottle when painting another model 6 months ago without this issue. I plan to sand another area with just water an a drop of soap next to see what happen.

I tried to post a picture to show what I was looking at, but the process is humbling, it is not a simple copy past process.
Since the last post I have sanded the model using water and the discoloration has not come back where I sanded. It really looked like a chemical process took place between the clear and the windex. This does not make since, because I had used the same windex to sand the last model I painted without a problem. The windex is approximately 1 year old if this makes a difference. I was looking at the cowling that was painted at the same time but not sanded and it did not discolor like the model, so this also leads me to think it was something in the sanding process used to cause the problem. I have had to sand down to the white paint to get rid of the discoloration.

I guess I got lucky using windex on the last two models and will use water for now on. The bright side is I am learning and the model this happened on is small.

Regards
Robert

Robert W · « **Reply #6 on:** May 26, 2008, 07:11:06 AM »

I have figured out how to post some photos to show what I was looking at. I know this is an old topic, but just wanted to make it more complete for future reference. The first shows the discoloration and the second shows the model finished. I sanded it back down to the white and then painted the model red wet sanding with water for the repaint.

I am of the belief that it was the Windex that caused the problem and will not use it again for wet sanding. I have since painted a profile using water without any issues.

afml · « **Reply #7 on:** May 26, 2008, 08:20:10 AM »

Hi Robert,

Great job on the Perky!

YES! I can relate to your problem.

However mine happened 3 days before the Nats!
All spraying was done outside.
Used Windex to wet sand previously with no difficulties.
Then the PINK WING virus hit!!
Tried everything in the place to get rid of it, but to no avail!
Chemical reaction fer sure!

OK...Gotta trim & fly this thing so..
Put on some more clear and try not to be too embarrased...

Shot some more clear/thinner/retarder. And.......

PINK GONE!

Tight lines!

Wes

Jim Treace · « **Reply #8 on:** May 28, 2008, 02:16:31 PM »

Don't use Windex (original) as wetting agent to put on silk. It leaves blue streaks.
I saw Windy's video and he used Windex as wetting agent in his spray bottle to keep the silkspan wet during covering. Says' it stays "wetter" longer, doesn't dry out as fast as water. So, I used it on silk. It left the blue streaks on the inside of the covering and you can't "wash" it out. Took several extra coats of white to cover it. I can still kind of see it when I hold the wing up to the light.
Jim

Author Topic: Painting question (Read 949 times)

Robert W

Painting question

Paul Smith

Re: Painting question

Robert W

Re: Painting question

Crist Rigotti

Re: Painting question

Randy Powell

Re: Painting question

Robert W

Re: Painting question

Robert W

Re: Painting question

afml

Re: Painting question

Jim Treace

Re: Painting question