Author Topic: Blushing dope (Read 3102 times)

Curare · « **on:** May 01, 2014, 05:18:11 AM »

Hey guys, just wondering if you might be able to shed some light on this little issue I'm having.

I've just silkspanned my chipmunk, and today (after 24 hours of drying time), I decided to get everything doped down nice. The weather has turned nasty here and outdoor temps were in the low teens (fifties in F˚) but the workshop was a few degrees warmer so I did the first coat in there.

As I normally do for the first shot after silkspanning I run a heavily thinned coat through the weave to get a nice stick. I went in there after letting in dry for an hour or so, and the whole plane is ghostly white. I've had a hell of a blush happen.

Upon thinking about it a little more, I had noticed that there were a lot of little areas that had blushed previously, even though I was brushing on, and the temp was warm.

I'm starting to think that maybe my dope is bad? Or I have contaminants in my thinner?

Any tests I can do to determine which one is toast?

55chevr · « **Reply #1 on:** May 01, 2014, 05:45:44 AM »

If you are painting in high humidity you can count on blushing. Recoat in lower humidity and it will clear.

Jim Thomerson · « **Reply #2 on:** May 01, 2014, 07:54:00 AM »

Use retarder. Next coat spray on about 50% retarder, then use maybe 5% in later coats. I have been known to brush on pure retarder to cure blush.

john e. holliday · « **Reply #3 on:** May 01, 2014, 08:24:49 AM »

I've had that happen on every plane that I put silkspan on wet with dope. Thin your dope to water consistency and put another coat on. It may surprise you.

55chevr · « **Reply #4 on:** May 01, 2014, 05:10:48 PM »

Retarder has to be used carefully as it will allow the paint to run much easier.

Curare · « **Reply #5 on:** May 01, 2014, 05:44:01 PM »

Where are you getting your retarder from?

55chevr · « **Reply #6 on:** May 01, 2014, 05:51:04 PM »

55chevr · « **Reply #7 on:** May 01, 2014, 05:53:01 PM »

You can just recoat on a low humid day and it will release the trapped moisture and clear the blush

Dennis Toth · « **Reply #8 on:** May 01, 2014, 06:34:01 PM »

Greg,
If you use your dope 50/50 and watch the temp/humidity you can usually find a time in the late morning that the temps go up a bit and the humidity drops below 65%, that's the time to paint. However, you really don't need to worry about the blush until you get to the final clear coats. After you brush on about 6 coats the weave gets filled and you are ready to go to color. Even the color can blush a bit cause before you go to final clear. That's the money shot.

Best, DennisT

Noel Corney · « **Reply #9 on:** May 01, 2014, 06:45:44 PM »

Any automotive paint supplier can supply you with retarder .

Allan Perret · « **Reply #10 on:** May 01, 2014, 07:08:21 PM »

Best to use same brand retarder as your dope and thinner. Brodak, Sig, and Randolph all have retarder. Don't know about Certified but would be surprised if they didn't.

Curare · « **Reply #11 on:** May 01, 2014, 07:21:53 PM »

Thanks for the input guys.

I know there's a paint supply store near here (my work) that does retarder. I was thinking about getting some to smooth out my clear coats, and obviously to reduce the occurance of blush.

Tim Wescott · « **Reply #12 on:** May 01, 2014, 09:36:23 PM »

To reduce the occurrence of blushing, don't tell those jokes where the paint can hear.

Curare · « **Reply #13 on:** May 02, 2014, 02:36:42 AM »

I also try not to paint naked.

Well, take two, I had the heater in the room running before hand, and it humidity was around 35% and it still blushed.

I'm now certain that it's not your typical blush, I think it might be from something in my thinner causing it.

Not that it really matters. Next up is grey primer so it can look as ugly as it wants. My main concern is that the blushing is indicative of the dope being compromised.

Serge_Krauss · « **Reply #14 on:** May 09, 2014, 04:11:24 PM »

Spray some thinner into the air slightly above the surface so that the mist settles onto the blushed area. It should clear up by releasing water captured by the dried outer dope layer(s).

SK

Curare · « **Reply #15 on:** May 09, 2014, 06:18:57 PM »

Serge, I should have tried that, instead I changed dopes (tautening to non tautening), and suddenly, no more blush!

Weird!

55chevr · « **Reply #16 on:** May 09, 2014, 09:13:20 PM »

Less humidity when you changed dope ... the next coat softens the skin and the moisture escapes.

Dennis Toth · « **Reply #17 on:** May 10, 2014, 07:34:38 AM »

Greg,
If you add retarder you need to let it dry about double the time before recoating. Also let it dry a couple weeks before you buff out to let the dope harden completely.

Best, DennisT

john e. holliday · « **Reply #18 on:** May 10, 2014, 09:01:50 AM »

Been putting clear dope on for the last couple of weeks and so far no blushing, of course the later coats have talc in the dope. It is Brodak clear with Brodak thinner.

Jim Thomerson · « **Reply #19 on:** May 10, 2014, 10:22:52 AM »

Some years ago a hobby shop bought five gallons of nitrate dope. I happened to have a bunch of new quart cans which I gave them. People complained that the dope was no good, and the hobby shop gave me a half dozen quart cans full. I tried it and it blushed like gangbusters. Added some retarder and it was fine.

Bill Little · « **Reply #20 on:** May 11, 2014, 06:41:44 AM »

Hi Greg,

I would not throw out the tautening dope just yet. When the weather improves it just might be fine for what you need to use it for. Really, tautening only needs to be applied to open bays, and then just enough to shrink up everything tight. That means that everything will be getting the non tautening over it and the original blushing will be a non problem. As you know, the new coat of dope melts the coats below it if applied properly so that you end up with "one coat" of dope on the model, "in a perfect world". They all melt together so to speak.

Be careful with retarder. It is basically a HOT THINNER. Thinners are "graded" for air temperature, hotter for cold weather so that it takes a bit longer to dry. Cooler for hot weather so that it dries a bit quicker. These qualities help reduce blushing. Retarder will really melt the lower coats so much that I have seen colors disappear!! I also have used too much retarder, which went all the way to the silkspan/wood and pulled up paint down to that level. I did not let it dry long enough for the dope to sufficiently harden back up.

WOW! that was longer than I intended, but remember, spray your final clear coats on a low humidity, mild temperature day.

BIG Bear
RNMM/AMM